Remarkable Enhancement of Thermoelectric Performance of Semicrystalline Polymer Films upon Incorporating A Nucleating Agent Additive

Remarkable Enhancement of Thermoelectric Performance of Semicrystalline Polymer Films upon Incorporating A Nucleating Agent Additive | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Remarkable Enhancement of Thermoelectric Performance of Semicrystalline Polymer Films upon Incorporating A Nucleating Agent Additive Yue Lin, Chen Chen, Haibao Ma, Kaiqing Lu, Xiaoxuan Zhang, Baiqiao Yue, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-5136690/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Nucleating agents are widely recognized for their ability to refine the solid-state morphology and microstructure of semi-crystalline polymers, significantly influencing their physicochemical properties. This study presents a simple yet effective strategy to dramatically improve the thermoelectric properties of semi-crystalline polymer films. By blending less than 1 wt% of the nucleating agent N,N'-(1,4-phenyl)diisonicotinamide (PDA) into Poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT-C14), we induce a controlled modulation of crystallization behavior, resulting in optimized microstructures with reduced structural disorder and improved charge carrier mobility. Systematic analysis of varying PDA concentrations identifies an optimal loading of 0.9 wt%, which yields a remarkable 45% increase in crystallinity relative to pristine PBTTT films. Under optimized doping conditions, the doped PBTTT-C14 film with 0.9 wt% PDA exhibits an exceptional electrical conductivity of 1800 S cm − ¹ and an optimal power factor of 150 µW m − 1 K − 2 , representing 105% and 384% improvements, respectively, over the doped pristine PBTTT-C14 film. These enhancements are primarily due to the synergistic effects of polymer chain extension and reduction of grain boundary size, which together mitigate grain boundary resistance and improve charge transport efficiency. Furthermore, the study elucidates the role of ion exchange doping in maintaining a high density of charge carriers without compromising the crystalline structure introduced by PDA. This research not only deepens the understanding of polymer thermoelectrics but also sets the stage for the development of innovative materials that could transform energy conversion technologies and polymer-based electronic devices. Physical sciences/Materials science/Soft materials/Polymers Physical sciences/Materials science/Materials for energy and catalysis/Thermoelectrics Figures Figure 1 Figure 2 Figure 3 Figure 4 1. Introduction In the quest for sustainable energy solutions, semiconductor polymers have garnered significant attention as viable materials for flexible thermoelectric applications 1 . Their inherent low thermal conductivity, combined with attributes such as processability, lightness, flexibility, and environmental compatibility 2 , 3 , make them ideal candidates for energy conversion technologies. Over the past decade, concerted efforts have propelled the power factors of thermoelectric polymers to hundreds or even thousands of µW m − 1 K − 2 . 4 Despite these advancements, polymer-based materials still lag behind their inorganic counterparts, such as PbSe crystals, which boast a record power factor of approximately 10,000 µW m − 1 K − 2 and average zT of 1.5 at 300 K 5 . Recent progress 6 has seen the development of polymer films with periodic heterogeneous structures, achieving a power factor of 347 µW m − 1 K − 2 at 298 K and a peak zT of approximately 1.28 at 368 K. This achievement underscore the potential of organic semiconductor polymers for efficient energy conversion. However, a significant performance gap remains, necessitating strategic advancements to enhance the thermoelectric performance of semiconductor polymers by refining their microstructure. The efficiency of thermoelectric materials, as quantified by the figure of merit \(\:zT=\frac{{S}^{2}\sigma\:}{\kappa\:}\) , hinges on optimizing electrical conductivity ( σ ) and the Seebeck coefficient ( S ) in conjunction with thermal conductivity ( κ ). The inherently low κ in conducting polymers places emphasis on the power factor ( \(\:{PF=S}^{2}\sigma\:\) ), directing research towards enhancing σ and S simultaneously. Achieving this, however, is challenging due to the inverse relationship between σ and S with increased charge density ( n ). A promising approach involves improving mobility while maintaining constant carrier concentration, thereby circumventing the inherent trade-off between σ and S 7 , 8 . For conjugated polymers, increasing crystallinity is a key strategy to enhance carrier mobility, as it promotes long-range order and facilitates efficient charge transport 9 . This approach has been successfully applied in the development of high-performance thermoelectric polymers, particularly in semicrystalline polymers derived from polythiophenes and donor-acceptor (D-A) copolymers 3 . These materials exhibit high crystallinity, which enables efficient charge transport and high power factors through meticulous molecular design 10 , 11 . However, validating these molecular designs can be time-consuming and labor-intensive due to the complexities involved in polymer synthesis. To address these challenges, alternative approaches such as polymer chain alignment have emerged. By reimagining solution processing techniques, researchers have achieved significant improvements in thermoelectric performance 3 , 12 , 13 . For example, a record power factor of 2900 µW m − 1 K − 2 was achieved in a polythiophene system through mechanical rubbing to align polymer chains 14 . Yet, this alignment tactic introduces anisotropic transport in polymer films, complicating the design of thermoelectric devices for real-world applications. Moreover, high crystallinity along the chain alignment direction often leads to increased thermal conductivity, which can diminish thermoelectric efficiency as dictated by the Wiedemann-Franz law 15 . Given these challenges, exploring alternative yet simple methods to create systems with superior crystallinity for polymer thermoelectrics is of significant interest. Nucleating agents are widely employed in traditional polymer industry to control crystallization kinetics and optimize the solid-state microstructures of bulk polymers 16 . These agents, including macromolecular additives like carbon nanotubes 17 , graphene 18 , and thiophene-containing copolymers 19 , have been effectively used to modify crystallization processes and improve the morphology of thin films, thereby enhancing targeted properties. More recently, supramolecular nucleating agents 20 have emerged as transformative additives, capable of dissolving uniformly in polymer melts at high temperatures and self-assembling into structured nanoarchitectures upon cooling. These agents can significantly enhance carrier mobilities in semicrystalline polymers like P3DDT 21 and P3HT 22 by up to 40-fold. Integrating such additives into doped semicrystalline polymers could be a promising approach to enhance their thermoelectric properties. However, several challenges remain, particularly whether the addition of nucleating agents will improve crystallinity and if the enhanced crystallinity introduced by the nucleating agent can be preserved during doping without compromising doping efficiency. To advance high-performance thermoelectric polymers using this strategy, it is essential to gain a comprehensive understanding of the interaction between nucleating agents and chemical doping, particularly its impact on microstructural evolution and charge transport within the nucleating agent-integrated polymer system. In the present study, we focus on Poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT), a thiophene-based semiconducting polymer renowned for its ordered microstructures and high charge carrier mobility 23 , as a foundational model system. We simply blend PBTTT-C14 with the nucleating agent N,N'-(1,4-phenyl)diisonicotinamide (PDA), targeting enhanced charge transport and thermoelectric properties. PBTTT's resilience to sequential doping allows it to maintain a high degree of structural order at high doping levels 24 , making it an ideal platform to explore the intricate interplay between structural morphology, charge transport, and thermoelectric performance. Our findings reveal that PDA markedly optimizes the crystallization behavior of PBTTT-C14, as substantiated by techniques like differential scanning calorimetry (DSC), atomic force microscopy (AFM) and grazing incidence wide-angle X-ray scattering (GIWAXS). The subsequent doping via the ion exchange (IEx) method amplifies these traits, leading to notable advancements in the electrical conductivity and thermoelectric properties. Notably, incorporating just 0.9 wt% PDA into PBTTT-C14 films minimizes structural disorder, demonstrating remarkable resilience to IEx doping, and achieving a high electrical conductivity of 1800 S cm − 1 alongside a maximum power factor approximating 150 µW m − 1 K − 2 , surpassing that of doped, pristine PBTTT-C14 films (σ max ~ 878 S cm − 1 and PF max ~ 31 µW m − 1 K − 2 ). We provide a comprehensive analysis of the mechanisms underlying this significant enhancement in charge transport and thermoelectric performance, drawing upon optical spectroscopy, thermal analysis, microstructural characterization, and transport measurements. This study highlights the strategic integration of nucleating agents as a simple approach to advance thermoelectric polymers, potentially revolutionizing the field of polymer-based thermoelectric materials for advanced scientific applications. 2. Results and Discussion 2.1. Incorporating A Nucleating Agent to Achieve Enhanced Crystallinity in Pristine PBTTT-C14 Films As highlighted earlier, the key objective of this study is to systematically regulate the crystallinity of a model semicrystalline polymer, specifically PBTTT-C14, to elucidate the complex relationship between microstructure, morphology, charge carrier transport, and thermoelectric performance, particularly under chemical doping conditions. Prior to the sequential IEx doping process, we firstly fine-tune the crystallinity of pristine polymer films, which are spin-coated from blending solutions with varying concentrations of the nucleating agent (Fig. 1 a; and see Experimental Section for details). We selected PDA, a supramolecular nucleating agent known for its remarkable ability to enhance the crystallinity of chemically similar polymer, such as Poly(3-hexylthiophene) (P3HT), with just 0.1 wt% loading 20 . Impressively, PDA significantly improves the crystallinity and crystalline domain size of PBTTT-C14, as corroborated by DSC, GIWAXS, and AFM. The results of these characterizations are discussed in detail below. We conducted a series of DSC experiments on PBTTT-C14/PDA blended samples, varying additive concentrations ranging from 0 wt% to 3.4 wt%, to probe the impact of nucleating agents on the crystallization kinetics of the polymer. All samples exhibit two primary thermal transitions (Fig. 1 b): a low-temperature transition (Transition I) occurring below 100 ℃, and a high-temperature transition (Transition II) centered around 220 ℃, which is characteristic of PBTTT's thermal behavior 25 . The effect of nucleating agents on Transition I is less pronounced, as indicated by the cooling curves in Fig. 1 b. Notably, the calorimetric peak corresponding to Transition II exhibits distinct variations with increasing PDA concentrations. Therefore, our further investigations focus on film samples annealed above the T c of Transition II, specifically the ribbon phase regime. The addition of PDA progressively raises the crystallization temperature (T c ) of PBTTT-C14, reaching 226.33 ℃ at a 0.9 wt% concentration, an increase of 3.04 ℃. Beyond this concentration, higher PDA loadings resulted in a decline in T c . This initial shift in T c to higher temperatures at low additive loadings, up to 0.9 wt%, suggests heterogeneous nucleation, which enhances the polymer's crystallization capacity 20 . The substantial improvement in crystallinity for these blended samples is directly evidenced by the increase in the enthalpy of crystallization (ΔH), a parameter proportional to the degree of crystallinity 26 . Specifically, the sample with 0.9 wt% PDA exhibited a ΔH peak of 16.69 J/g at transition II (Fig. 1 c), representing a 45% increase compared to pristine PBTTT films. However, at higher PDA concentrations, the degree of crystallinity declined, as evident by notable reductions in both T c and ΔH. This reduction in crystallinity can be attributed to the overloading of the nucleating agent. Overuse of nucleating agents might lead to an excessively high nucleation rate, resulting in the formation of numerous small and imperfect crystalline grains. This high nucleation rate impedes further crystal growth, ultimately leading to a decrease in overall crystallinity 27 . GIWAXS analysis was employed to investigate the evolution of crystalline order in pristine PBTTT-C14 and PBTTT-C14/PDA blended films across various nucleating agent concentrations. Both pristine and blended films exhibit high crystallinity, characterized by four orders of (h00) diffraction peaks along the q z axis, representing the lamellar stacking direction, and two additional peaks at 1.45 Å −1 and 1.71 Å −1 on the q xy axis, corresponding to the polymer backbone and π-stacking orientation, respectively (Fig. 1 d-f; and Figure S1 in the Supporting Information). Overall, the 2D GIWAXS scattering patterns reveal a remarkable similarity between the samples, with enhanced diffraction intensities along the in-plane q xy directions for the film containing 0.9 wt% of the nucleating agent. To further explore the molecular stacking behavior upon the incoporation of the nucleating agent, we analyzed the 1D line-cut scattering profiles (Figure S1 ) and extracted crystallographic parameters, summarized in Table S1 . For the film with 0.9 wt% PDA, no notable changes in paracrystallinity ( g π−π ) and higher coherence length ( L c ) were observed. These observations suggest that while there is a significant enhancement in crystallinity, the molecular stacking behavior of PBTTT-C14 is largely preserved up to an optimal concentration of PDA. The morphological changes in the polymer films due to the addition of PDA were examined using AFM. The height image in Fig. 1 g shows that the pristine PBTTT-C14 thin film, annealed at 260 ℃, exhibits uniform ribbons-like structures with an average width of 53.18 nm, a characteristic feature of films annealed from a smectic, liquid crystalline phase (Transition II) 28 . These ribbons consist of crystalline domains that maintain a smectic chain arrangement, typically comprising multiple chain-extended or chain-folded polymer chains, depending on the degree of chain alignment in the solid state 29 . Upon the initial incorporation of PDA, the ribbon structure was preserved, with the ribbon width increasing by 62%, from 53 nm in the pristine film to 86 nm at 0.9 wt% nucleating agent, indicating a tendency for aggregation. However, at a higher PDA concentration of 3.4 wt%, the ribbon width decreased to 42 nm. This transformation is accompanied by the gradual blurring of the nanofibrillar structure, suggesting a loss of long-range fiber periodicity (Fig. 1 i; and Figure S3 in the Supporting Information). These observations imply that the addition of PDA at low concentrations (up to 0.9 wt%) enhances the degree of crystallinity and promotes the growth of individual ribbons, which is crucial for improving both structural order and charge transport. The observation of enlarged crystalline domains (ribbons) coupled with narrower grain boundaries at an optimal PDA loading suggests that the PBTTT-C14/PDA blended system may serve as a viable platform for subsequent doping and thermoelectric property investigations. Such a highly ordered microstructural morphology is anticipated to facilitate both efficient intradomain and interdomain charge transport. 2.2. Preserving Superior Structural Order in PBTTT-C14/PDA Blended Films upon Ion Exchange Doping Chemical doping plays a pivotal role in modulating the electronic and thermoelectric properties of polymer semiconductors, effectively adjusting the energy level and optimizing the charge concentration n. 11 However, achieving optimal thermoelectric conversion in a polymer system often necessitates a charge concentration n surpassing 10 19 cm − 3 , which may significantly disturb the molecular packing within the neat polymer matrix, potentially compromising the high carrier mobility µ derived from its high crystalline order 30 . To harness the enhanced crystallinity of PBTTT-C14 films induced by the nucleating agent for enhancing thermoelectric performance, we adopted a newly developed IEx doping method. This doping technique has exhibited remarkable efficacy in achieving doping concentrations exceeding 10 20 cm − 3 , while imparting minimal or even positive effects on the microstructure and morphology of the polymer films. This preservation of superior structural order is critical for maintaining efficient charge transport. The successful achievement of efficient doping and preservation of superior structural order in PBTTT-C14/PDA blended films was confirmed through spectroscopic, GIWAXS, and AFM characterizations (Fig. 2 and Figure S2, S4 in the Supporting Information). The extent of doping in all polymer films, with varying PDA concentrations, both before and after IEx doping, was evaluated using Ultraviolet-Visible-Near Infrared (UV-Vis-NIR) spectroscopy. For all the blended films studied, the neutral π-π * band centered around 550 nm exhibited nearly complete bleaching (Fig. 2 a; and Figure S5 in the Supporting Information), a trend consistent with the pristine PBTTT film (Figure S5). Simultaneously, two broad absorption bands, labelled P1 and P2, appeared at wavelengths > 2000 nm and around 800 nm, respectively. These absorption bands are indicative of polaron or multi-polaron states, as commonly observed in highly doped PBTTT films 24 , 31 . These UV-Vis-NIR absorption profiles suggest the blended films obtained at high doping levels comparable to those of pristine PBTTT-C14, with a doping concentration around 10 21 cm − 3 , corresponding to roughly one charge per monomer unit. This high carrier density, confirmed for both pristine and blended systems, is further validated by Hall effect analysis presented in Section 4 of the Supporting Information. Fourier Transform Infrared Spectroscopy (FT-IR) was employed to investigate the degree of polaron delocalization in doped films (Fig. 2 b). Polaron delocalization can be effectively assessed by examining polaron-induced absorption features in the mid-infrared (mid-IR) region 32 , 33 . Upon doping, the P1 band peaks around 1800 cm − 1 with a weak shoulder below 1500 cm − 1 , corresponding to intrachain and interchain transitions, respectively 32 . Additionally, a number of narrow peaks are superimposed between 400 cm − 1 and 1475 cm − 1 , which are typically interpreted as infrared active vibrational modes (IRAVs). The intensity of the IRAVs is an indicator of the extent of polaron delocalization along the polymer chains and between chains. The more intense the IRAVs, the greater the degree of polaron delocalization 34 . In the FT-IR spectra of the doped blended films, the pronounced IRAV peaks suggest that a high level of polaron delocalization was achieved via ion exchange doping, similar to that observed in pristine PBTTT-C14 films 35 , 36 . GIWAXS characterization was employed to examine the microstructural changes in both pristine PBTTT-C14 and PBTTT-C14/PDA blended films after IEx doping. As depicted in the 2D diffraction patterns in Fig. 2 d-f, all doped films retain their lamellar packing, featuring an edge-on orientation of the polymer backbone and considerable long-range crystallinity. Both the well-ordered out-of-plane peaks (h00) and in-plane stacking peaks remain clearly visible, resembling their undoped counterparts. Upon IEx doping, the lamellar spacing notably expands for both the pristine and blended films, for instance, from 20.937 Å to 26.449 Å for the 0.9 wt% blended sample. This expansion suggests that the counterions predominantly integrate into the alkyl side-chain regions, consistent with previous findings on semicrystalline polythiophenes 36 – 38 . Interestingly, a reduction in the π-π stacking distance is observed across all samples: in the pristine film, this distance decreases from 3.601 Å to 3.526 Å (Fig. 2 d; and Table S2 in the Supporting Information), while in the 0.9 wt% and 3.4 wt% blended films, it reduces from 3.646 Å to 3.516 Å and from 3.654 Å to 3.524 Å, respectively (Fig. 2 e-f; and Table S2 in the Supporting Information). This reduction can be attributed to the strengthening of polaronic coupling between chains, facilitated by the IEx doping process 36 . Furthermore, all three films display a ~ 10% decrease in paracrystallinity parameter (g π−π ) compared to their undoped states, suggesting that ion exchange doping effectively enhances structural order without causing discernible disruption, even in the presence of nucleating agent additives (Table S2 in the Supporting Information). The high electrical conductivities of both the pristine and blended systems, with σ max ranging from 878 to 1800 S cm − 1 , are strongly correlated with reduced paracrystalline disorder, in line with previous findings in high-mobility semicrystalline polymers and donor-acceptor copolymers 36 . It is important to note the differences in charge transport and thermoelectric properties between the pristine and blended systems. In particular, the doped 0.9 wt% blended system achieves a conductivity of approximately 1800 S cm − 1 and an exceptional thermoelectric power factor of about 150 µW m − 1 K − 2 (as disscussed in Section 2.3 and 2.4). These remarable enhancements cannot be solely attributed to molecular packing, as there are no significant differences in paracrystallinity and coherence length between doped pristine PBTTT film and 0.9 wt% blended film (Table S2 in Supporting Information). Instead, the enhanced thermoelectric performance in the blended systems can be primarily linked to a notable increase in crystallinity, as demonstrated through detailed microstructural and morphological analyses of the undoped counterparts. In conclusion, the GIWAXS analysis reveals that the counterions primarily occupy the side-chain regions, while IEx doping enhances backbone planarization, promoting efficient charge transport in all doped films—especially in the 0.9 wt% PBTTT-C14/PDA blended system. Overall, the introduction of the nucleating agent into PBTTT-C14 does not significantly interfere with the IEx doping process, enabling highly effective doping while maintaining or even improving the superior crystalline order. 2.3. Thermoelectric Properties of Ion Exchange Doped PBTTT-C14/PDA Blended Films We now turn our attention to the thermoelectric performance of the ion exchange (IEx) doped PBTTT-C14/PDA blended films. As shown in Figs. 3 a and 3 b, the electrical conductivity (σ) and Seebeck coefficient (S) of these doped polymers exhibit distinct trends as a function of PDA concentration, ranging from 0 wt% to 3.4 wt%. Specifically, Fig. 3 a shows a significant increase in electrical conductivity, reaching a peak value of 1178 S cm − 1 at 0.9 wt% PDA loading with a doping concentration of 3 mM. This represents an 85% enhancement compared to the conductivity of the doped pristine PBTTT-C14 film under the same doping conditions. This improvement is consistent with the crystallinity evolution with PDA concentration, as discussed in Section 2.1 . Notably, the Seebeck coefficient follows a similar trend, decoupling from the electrical conductivity. The doped 0.9 wt% blended film exhibits a maximum Seebeck coefficient of approximately 36 µV K − 1 , which is 148% higher than that of the doped pristine film. As a result, the power factor (PF) of the doped 0.9 wt% blended film attains an impressive 150 µW m − 1 K − 2 , representing a remarkable 1011% improvement over the pristine film at an equivalent doping concentration, as shown in Fig. 3 c. The inset of Fig. 3 c further emphasizes the competitive advantage of our IEx doped 0.9 wt% blended system when compared to other unaligned benchmark systems, achieved through morphology control 39 , doping engineering 40 , 41 . Remarkably, this optimal performance is on par with a recently developed highly oriented PBTTT system 42 , which, despite requiring complex processing techniques—such as controlled tie chain incorporation through polymer blending coupled with large-scale alignment—results in notable charge transport anisotropy. The simultaneous increase in both σ and S, leading to a substantial enhancement in the PF with the appropriate PDA additive loading, is unprecedented. The detailed mechanisms underlying this phenomenon are elaborated in Section 2.4. To further fine-tune the thermoelectric performance of the 0.9 wt% blended system, we optimized the S and σ as a function of doping concentration. For comparison, the same experiment was performed on a pristine PBTTT-C14 system to better understand the impact of PDA additives on thermoelectric properties. As shown in Fig. 3 d, the electrical conductivity initially increases with rising doping concentration, peaking at approximately 7 mM for the doped 0.9 wt% blended system. At this concentration, the blended film achieves an electrical conductivity of 1800 S cm − 1 , more than double the maximum conductivity of 878 S cm − 1 observed in the doped pristine system at a doping concentration of 12.5 mM. In terms of the Seebeck coefficient, both the blended and pristine systems exhibit a comparable downward trend with increasing doping concentration. Consequently, the calculated power factors are presented in Fig. 3 f. Notably, the ion exchange doped PBTTT-C14/PDA blended films reach a significantly higher maximum power factor of 150 µW m − 1 K − 2 , far surpassing the 31 µW m − 1 K − 2 achieved by the doped pristine counterpart. These findings underscore the promising potential of nucleating agent additive engineering in significantly enhancing the thermoelectric performance of high-performance semicrystalline conjugated polymers. A comparative analysis of the thermoelectric properties between blended and pristine systems reveals that the remarkable PF achieved by the IEx doped PBTTT-C14/PDA blend (0.9 wt%) is primarily driven by its exceptional charge transport properties. To further investigate, we explored the charge transport physics to uncover the fundamental mechanisms by which the nucleating agent facilitates improved charge transport in the doped PBTTT systems. 2.4. Mechanisms Underlying the Remarkable Enhancement in Charge Transport and Thermoelectric Performance of IEx Doped PBTTT-C14/PDA Blended Films Charge transport measurements are essential for characterizing transport parameters in semiconducting materials, allowing for the correlation between microscopic spatial and energetic distributions through microstructural characterization and charge transport models 43 . For doped polymer semiconductors, temperature-dependent measurements of electrical conductivity, the Seebeck coefficient, and the Hall coefficient provide insight into the dominant transport mechanisms—whether they involve localization (hopping-like) or delocalization (metal-like)—that govern electronic transport 44 – 46 . In this study, we applied this experimental framework to investigate how the incorporation of a nucleating agent additive affects charge transport physics and the microstructural characteristics of PBTTT-C14 films subjected to sequential ion exchange doping. Figure 4 a depicts the temperature (T) dependence of electrical conductivity for both pristine and blended films doped at a concentration of 5 mM, highlighting the significant effect of PDA concentration. Across all systems the temperature dependence of conductivity reflects that of high conductivity PBTTT, characterized by a plateau or slight decrease above 250 K, particularly prominent in the 0.9 wt% blended system. The appearance of a conductivity peak suggests a shift toward metallic conduction rather than thermally activated hopping conduction, especially at grain boundaries 42 . To quantify the thermal activation energy (E a ) governing each sample's conductivity, we applied the Arrhenius equation (see Supporting Information Section 5). The E a , which reflects energetic disorder within integer charge transfer complex (ICTC) states 47 , decreases from 3.25 meV in pristine PBTTT to 2.67 meV at 0.9 wt% PDA loading, where conductivity peaks (Fig. 4 b, upper panel). This minimal E a in the 0.9 wt% blended sample signifies the lowest energetic disorder, which can be attributed to optimal crystallinity and structural ordering (Sections 2.1 & 2.3 ). As a result, the 0.9 wt% blended film achieves a peak charge carrier mobility of 2.92 cm 2 V − 1 s − 1 , confirmed by Hall effect measurements (Fig. 4 e). Additionally, by fitting the Seebeck coefficient-conductivity (S-σ) data using the Kang-Snyder model 48 (see the Supporting Information Section 6 for more details), we derived the energy barrier for charge percolation between ordered domains, denoted as W γ . Unlike E a , which provides insights into the overall transport mechanism encompassing both intra- and inter-domain transport, W γ specifically offers insights into inter-domain transport, providing a macroscopic perspective on conductivity across crystalline regions 48 , 49 . W γ follows a trend similar to E a (Fig. 4 b, bottom panel), reaching its minimum at intermediate PDA concentrations before slightly increasing at higher concentrations, likely due to decreased overall crystallinity from excessive PDA loadings, as observed in DSC, GIWAXS, and AFM data discussed earlier. Notably, the decreasing ratio of W γ to E a with increasing PDA concentration (Fig. 4 c) suggests that inter-domain energetic disorder plays a diminished role in limiting conductivity and carrier mobility. To further investigate the synergistic impact of nucleating agent additive engineering and IEx doping on the charge transport properties of PBTTT-C14, we conducted comparative analyses of the S-σ relationship (Fig. 4 d) across varying doping concentrations for both pristine and 0.9 wt% blended systems. By applying the Kang-Snyder model to the S-σ relationship, we observe that a single parameter set (s and σ E0 ) inadequately describes the entire conductivity range (See the Supporting Information Section 6 for more details). Notably, both systems exhibit a distinct change in charge transport characteristics around 200 S cm − 1 , transitioning from s = 3 to s = 1 with increasing conductivity. This transition is generally indicative of an insulator-to-metal transition occurring in semicrystalline polymer systems, particularly when carrier densities exceed 10 21 cm − 3 40, 50 . In both the 's = 3' and 's = 1' regimes, the 0.9 wt% blended system demonstrates notably higher σ E0 values, specifically 0.03 S cm − 1 and 120 S cm − 1 , respectively, which are approximately more than 2 times greater than those of the pristine system. Since σ E0 acts as a weighted mobility factor tied to intrinsic carrier mobility 49 , 51 , this observation highlight the enhanced charge transport capability of the doped 0.9 wt% blended system. This superiority is further evidenced by the consistently higher Hall mobility measurements across the entire conductivity spectrum (Fig. 4 e). Consequently, the 0.9 wt% blended system exhibits significantly improved electrical conductivity for a given Seebeck coefficient, resulting in a substantially higher PF. A comprehensive correlation analysis between transport measurements and microstructural characterization data allowed us to formulate a physical model (Fig. 4 f) that elucidates the mechanism behind the enhanced charge transport properties induced by the nucleating agent additive. Upon incorporating an optimal concentration (0.9 wt%) of PDA, PBTTT-C14 films experience a significant increase in crystallinity, as demonstrated by DSC analysis. This increase is accompanied by improved structural order at the grain boundaries without disrupting the crystalline lattices within the domains. The polymer chain extension, supported by AFM and GIWAXS characterizations, contributes to this enhanced structural order. Such improvements are preserved, and in some cases intensified, across a broad range of carrier concentrations through ion exchange doping (Section 2.2 ). Recent experimental and theoretical investigations have underscored structural disorder, rather than Coulombic trapping, as the primary determinant limiting charge transport in doped polymers, especially at high doping levels 24 , 52 . This explains the superior carrier mobility of the doped 0.9 wt% blended system, which achieves substantially higher electrical conductivities compared to the unblended system when sufficient charge densities are introduced. Specifically, the chain extension reduces grain boundary sizes and promotes the formation of tie chains that bridge adjacent crystalline domains by clustering together. This enables charge carriers to traverse domains without relying on interchain hopping through disordered regions. This dual effect—grain boundary size reduction and tie chain formation—significantly alleviates energetic disorder at grain boundaries, as evidenced by the substantial decreases in the activation energies E a and the transport energy barriers W γ . The macroscopic resistance of the 0.9 wt% system is therefore reduced, with grain boundary resistance often being a major limiting factor for conductivity in many polymer semiconductors 42 , 53 . Additionally, the enhanced crystalline order within domains after IEx doping, indicated by reduced g π−π values, fosters intradomain charge transport, promoting two-dimensional charge carrier delocalization. This further reduces the overall energetic disorder and lowers E a . This synergistic improvement in both intra- and inter-domain charge transport, stemming from nucleating agent additive engineering and ion-exchange doping, results in a record-high electrical conductivity of approximately 1800 S cm − 1 and an outstanding thermoelectric performance, with a PF of 150 µW m − 1 K − 2 for PBTTT-C14 films. 3. Conclusion In summary, we propose a straightforward yet highly effective conceptual approach that utilizes nucleating agents to precisely control the crystallization behavior of semicrystalline polymer semiconductors, thus thermoelectric performance. This method presents a clear pathway to enhance charge transport and achieve outstanding thermoelectric performance by increasing the degree of crystallinity without compromising the molecular packing order, while also improving electrical connectivity within doped polymer films. Through meticulous assessment of microstructural evolution driven by nucleating agents and IEx doping, we identified 0.9 wt% as the optimal PDA loading for achieving superior structural ordering. Remarkably, this ordering remains robust, even slightly improving after doping. As a result, structural disorder is minimized, and charge carrier mobility is maximized in highly doped PBTTT-C14 films, leading to exceptional transport properties, including a Hall mobility of up to 2.92 cm 2 V − 1 s − 1 , electrical conductivity reaching 1800 S cm − 1 , and a power factor close to 150 µW m − 1 K − 2 . Our approach breaks through the conventional barriers limiting the thermoelectric performance of polymer semiconductors by significantly boosting conductivity without reducing the Seebeck coefficient. This enhancement is primarily due to the reduction in grain boundary size facilitated by nucleating agent engineering, coupled with a modest increase in crystalline order within domains, further amplified by IEx doping. Importantly, this methodology holds broad applicability across various semicrystalline polymers, potentially driving significant advances in fast charge transport in highly doped conjugated polymers, ultimately contributing to the development of high-performance thermoelectric materials for next-generation organic electronics. 4. Experimental Section Sample Preparation : Materials Poly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT-C14) was purchased from Sigma-Aldrich. N,N'-(1,4-phenylene)diisonicotinamide (PDA, > 97% purity), acetonitrile (ACN, > 99.9% purity, water content 98% purity, water content 99.99% purity) and 1-Butyl-1-Methylpyrrolidinium Bis(trifluoromethylsulfonyl)imide (BMP-TFSI, > 99% purity, water content < 0.04%) were obtained from Aladdin. All reagents were used as received, without further purification. Blend solution preparation PBTTT-C14 was dissolved in DCB at a concentration of 10 g/L, with heating to 110°C and stirring for 2 hours, followed by filtration through a 0.22 µm PTFE membrane. PDA was dispersed in DCB at 1 g/L with 2 hours of stirring. Defined volumes of PBTTT-C14 and PDA solutions were mixed, and the mixture was heated and stirred at 110°C for an additional hour. Dopant solution preparation BMP-TFSI solutions were prepared in ACN at concentrations of 250, 500, 750, 1000, and 1500 mM, and FeCl 3 solutions were prepared in ACN at concentrations of 2.5, 5, 7.5, 10, and 15 mM. Dopant mixtures were obtained by combining appropriate volumes of BMP-TFSI and FeCl 3 solutions (e.g., 250 mM BMP-TFSI solution with 2.5 mM FeCl 3 solution can be configured to produce a 0.25 mM mixed dopant solution). The mixed dopant solution concentration was set to 0.25, 0.5, 0.75, 1, 3, 5, 7, 10, 12.5 mM. The FeCl 3 solutions were freshly prepared before use. All solutions were prepared in an argon-filled glove box (< 1 ppm H 2 O and O 2 ). Thin film preparation : The solutions were spin-coated onto preheated substrates at 1500 rpm for 60 seconds using preheated pipettes. Following deposition, films were annealed at 260°C for 20 minutes and cooled at a controlled rate of 2°C/min to room temperature to promote the formation of a ribbon phase. For doping, 150 µL cm − 2 of dopant solution was applied to the films, left for 60 seconds, and then the excess solution was removed by spin-coating at 7000 rpm for 60 seconds. Afterward, the films were rinsed with acetonitrile to eliminate residual dopants. For electrical measurements, a protective layer of Cytop was spin-coated onto the films using a diluted Cytop solution (Cytop:solvent = 1:2) at 2000 rpm for 60 seconds. All procedures were carried out in an argon-filled glove box. Sample Preparation for Characterization : Electrical and seebeck measurements Samples were fabricated on 13 mm × 6 mm glass substrates with 10 nm-thick gold electrodes (1.5 mm wide). Hall effect measurements Samples were prepared on 10 mm × 10 mm glass substrates with 2 mm × 2 mm gold electrodes deposited at the corners. GIWAXS samples Prepared on 10 mm × 10 mm silicon substrates. UV-Vis and FTIR samples Prepared on glass substrates of comparable dimensions. Characterization Methods : Differential scanning calorimentry (DSC) PBTTT-C14/PDA samples were analyzed using a TA Discovery25 under nitrogen. Samples were annealed at 280°C for 5 minutes and cooled at 10°C/min to -80°C. Conductivity and Seebeck Coefficient Measurements Conductivity and Seebeck coefficient were measured using a ULVAC-RIKO ZEM-3 system under helium. Film thickness was determined by AFM (Bruker Dimension Icon), and conductivity was measured via the four-probe method. Seebeck coefficients were obtained through the linear fitting of ΔV vs. ΔT. Ultraviolet-Visible-Near Infrared Spectroscopy (UV-Vis-NIR) Spectra were recorded using a Lambda365 instrument over a range of 250–2500 nm with 2 nm intervals. Substrate background spectra were collected separately as the baseline. Fourier-transform infrared spectroscopy (FTIR) : FTIR spectra were obtained on a Bruker Vertex 70 spectrometer over the 400–4000 cm − 1 range, with a 4 cm − 1 interval. Atomic force microscopy (AFM) : Tapping-mode AFM was conducted on a Bruker Dimension Icon system to characterize the surface morphology. The ribbon width was determined by averaging measurements from at least thirty randomly selected ribbons. Grazing incidence wide angle X-ray scattering (GIWAXS) Measurements were performed using the Xenocs Xeuss 3.0 system with an 8.04 keV X-ray source and an EIGER2 detector positioned 80 mm from the sample. Data were recorded with a 0.18° incident angle and analyzed using GIWAXS-Tools software. Coherence length and paracrystallinity were calculated using convolution Gaussian and Lorentzian fittings 54 (see Section 1 in the Supporting Information for more details). Hall effect Measurement Hall measurements were performed on an ET9000 Hall instrument modified with the reverse field reciprocity theorem 55 – 57 . The setup included Keithley 6220, 2182A, and 6485 instruments, achieving 10 fA current and 1 nV voltage resolutions. Measurements were conducted with a 1000 nA current and a magnetic field of 18 kG. Film thicknesses were measured by AFM. Declarations ACKNOWLEDGMENT We acknowledge support from the National Natural Science Foundation of China (52273029, 52203022), Fujian Science & Technology Innovation Laboratory for Optoelectronic Information of China (2021ZZ119), the Pilot Project of Fujian Province (2022H0037), Fuzhou Technology Innovation Platform (2022-P-020), Natural Science Foundation of Fujian Province for Distinguished Young Scholars (2023J06045), and Fujian– CAS joint STS Project (2023T3064). C.C. acknowledges support from the Hunan Provincial Natural Science Foundation of China (2022JJ40547), and the University of Defense Technology Research Project (ZK22-15). References Russ B, Glaudell A, Urban JJ, Chabinyc ML, Segalman RA (2016) Organic thermoelectric materials for energy harvesting and temperature control. Nat Rev Mater 1 Wang SH, Zuo GZ, Kim J, Sirringhaus H (2022) Progress of Conjugated Polymers as Emerging Thermoelectric Materials. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-5136690","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":363014428,"identity":"f49b4d18-fc19-4faf-bf8b-69dd5b2f4fef","order_by":0,"name":"Yue Lin","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAz0lEQVRIiWNgGAWjYBACPmYwZcPP2EysFjaIljTJRuK1QKjDkg1EO4yNnfeYNE/FeQnmdt7Hn24w2MkzsJ89QMBhfGnSPGduSzA2s5tJ5zAkGzbw5CUQ0MJjJs3bdruOsZmNjTmHgTmBQYLHgAgt/84BbWFj/pzDUE+sloYDIC0MQIcdJkqLseWcY8kgLWzSOQbHDdt4cvBr4ec/Y3jjTY2dhGH/MaDDKqrl+dnP4NcCBCwSINKwAUQawGMKL2D+ACLliVA5CkbBKBgFIxQAALxJL3GieL/5AAAAAElFTkSuQmCC","orcid":"https://orcid.org/0000-0001-9196-9180","institution":"Chinese Academy of Sciences","correspondingAuthor":true,"prefix":"","firstName":"Yue","middleName":"","lastName":"Lin","suffix":""},{"id":363014429,"identity":"68531666-f2fa-4ed8-bd7c-efc7b2533505","order_by":1,"name":"Chen Chen","email":"","orcid":"","institution":"National University of Defense Technology","correspondingAuthor":false,"prefix":"","firstName":"Chen","middleName":"","lastName":"Chen","suffix":""},{"id":363014430,"identity":"6150428a-8563-47b5-a469-66650b2381b6","order_by":2,"name":"Haibao Ma","email":"","orcid":"","institution":"Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences","correspondingAuthor":false,"prefix":"","firstName":"Haibao","middleName":"","lastName":"Ma","suffix":""},{"id":363014431,"identity":"24f9adf2-e4ab-47ca-a4cc-7e0730efaad4","order_by":3,"name":"Kaiqing Lu","email":"","orcid":"","institution":"Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences","correspondingAuthor":false,"prefix":"","firstName":"Kaiqing","middleName":"","lastName":"Lu","suffix":""},{"id":363014432,"identity":"70a0ec28-6338-431f-91c8-747b68b5f5b0","order_by":4,"name":"Xiaoxuan Zhang","email":"","orcid":"","institution":"Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences","correspondingAuthor":false,"prefix":"","firstName":"Xiaoxuan","middleName":"","lastName":"Zhang","suffix":""},{"id":363014433,"identity":"8abc4d88-33c9-49dd-b757-d15d0c611c46","order_by":5,"name":"Baiqiao Yue","email":"","orcid":"","institution":"Chinese Academy of Sciences","correspondingAuthor":false,"prefix":"","firstName":"Baiqiao","middleName":"","lastName":"Yue","suffix":""},{"id":363014434,"identity":"7a0e7e66-592b-4482-bf4e-2f23b440b02c","order_by":6,"name":"Ce Song","email":"","orcid":"","institution":"National University of Defense Technology","correspondingAuthor":false,"prefix":"","firstName":"Ce","middleName":"","lastName":"Song","suffix":""},{"id":363014435,"identity":"3f31e867-f2a9-48b9-8fcf-05cbdc480a29","order_by":7,"name":"Pochong Huang","email":"","orcid":"","institution":"Fujian Science \u0026 Technology Innovation Laboratory for Optoelectronic Information of China","correspondingAuthor":false,"prefix":"","firstName":"Pochong","middleName":"","lastName":"Huang","suffix":""},{"id":363014436,"identity":"ed150b17-f8fd-4b30-97e3-642122ca6b9c","order_by":8,"name":"HaiFeng Cheng","email":"","orcid":"","institution":"National University of Defense Technology","correspondingAuthor":false,"prefix":"","firstName":"HaiFeng","middleName":"","lastName":"Cheng","suffix":""}],"badges":[],"createdAt":"2024-09-23 09:05:13","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-5136690/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-5136690/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":66246893,"identity":"6e34731e-4cd5-4591-b7ee-96ad905817f4","added_by":"auto","created_at":"2024-10-09 08:00:58","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":890920,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThermal Behavior, Microstructure, and Surface Morphology of PBTTT-C14 Films with Varying PDA Additive Concentrations: \u003c/strong\u003e(a) Chemical structure of materials used and sample preparation methods; (b) DSC curves for pristine and PDA-blended PBTTT-C14 films at different concentrations (0.5, 0.9, 2.5, and 3.4 wt%); (c) Enthalpy of crystallization at Transition II from the DSC curves as a function of PDA concentration; (d-f) GIWAXS images for films containing different concentrations of PDA; (g-i) AFM images showing surface morphology corresponding to the different PDA concentrations.\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-5136690/v1/8a5a306c8d7fe22b97e3af8c.png"},{"id":66245972,"identity":"337fcc49-b167-456d-a2be-6c41151ac031","added_by":"auto","created_at":"2024-10-09 07:52:58","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":734362,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eThe doping effects on the optical characteristics and structural ordering of pristine and PBTTT-C14/PDA blended films:\u003c/strong\u003e (a) UV-vis-NIR absorption spectra of 0.9 wt% blended films before and after doping; (b) FT-IR absorption spectra of pristine and PBTTT-C14 films at different PDA concentrations (0.5, 0.9, 2.5, and 3.4 wt%) after doping; (c) Paracrystallinity extracted from GIWAXS data for pristinefilms and blended films at 0.9 wt% and 3.4 wt% concentrations; (d-f) GIWAXS imagesof pristinefilms and blended films at 0.9 wt% and 3.4 wt% concentrations after doping.\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-5136690/v1/b4abdaa7bce44648ec7ea183.png"},{"id":66245967,"identity":"9d6d3273-c79b-444a-9636-c83380222049","added_by":"auto","created_at":"2024-10-09 07:52:58","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":253044,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eEffect of PDA additive incorporation on thermoelectric properties of PBTTT-C14:\u003c/strong\u003e The Conductivity (a), Seebeck coefficient (b) and power factor (c) as a function of nucleating agent concentration at the doping concentration of 3 mM; (d-f) Comparison of the Conductivity (d), Seebeck coefficient (e) and power factor (f) as a function of dopant concentration for pristine and 0.9 wt% blended systems.\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-5136690/v1/a0a6f496e86d3b00ff82c4c2.png"},{"id":66245968,"identity":"2168b6f5-f73c-424e-8eee-700e5255e4ea","added_by":"auto","created_at":"2024-10-09 07:52:58","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":488885,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eComparative analysis of charge transport modulation of doped PBTTT-C14/PDA blends\u003c/strong\u003e: (a) Temperature dependence of conductivity at varying PDA concentrations. (b) Arrhenius activation energy (E\u003csub\u003ea\u003c/sub\u003e) and transport energy barrier (W\u003csub\u003eγ\u003c/sub\u003e) extracted from the temperature dependence of conductivity and Seebeck-Conductivity relationship data, respectively. (c) Ratio of W\u003csub\u003eγ\u003c/sub\u003e to E\u003csub\u003ea\u003c/sub\u003e across different PDA concentrations. Comparison of relationship between Seebeck coefficient and conductivity (d) as well as Hall mobility (e), plotted against doping concentration, for nucleating agent concentrations of 0 and 0.9 wt%. (f) Illustration of microstructure and morphology features of pristine and 0.9 wt% blended films at doped states. Illustration of microstructure and morphology characteristics of pristine films and films blended with 0.9 wt% PDA, both at doped states\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-5136690/v1/8f7f84ec19aa853b28887520.png"},{"id":68536981,"identity":"347c1667-b12e-42a5-a06c-3ab2e9915630","added_by":"auto","created_at":"2024-11-08 10:19:08","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3342877,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5136690/v1/dfec4cfd-e6f9-461c-a15c-031da0e31f1f.pdf"},{"id":66245970,"identity":"255c11fd-8060-4998-bd81-d82b7d1949bc","added_by":"auto","created_at":"2024-10-09 07:52:58","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":3149213,"visible":true,"origin":"","legend":"","description":"","filename":"SI.docx","url":"https://assets-eu.researchsquare.com/files/rs-5136690/v1/954b230e6fdcdf7e798df0e0.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Remarkable Enhancement of Thermoelectric Performance of Semicrystalline Polymer Films upon Incorporating A Nucleating Agent Additive","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eIn the quest for sustainable energy solutions, semiconductor polymers have garnered significant attention as viable materials for flexible thermoelectric applications\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u003c/sup\u003e. Their inherent low thermal conductivity, combined with attributes such as processability, lightness, flexibility, and environmental compatibility\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e,\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e, make them ideal candidates for energy conversion technologies. Over the past decade, concerted efforts have propelled the power factors of thermoelectric polymers to hundreds or even thousands of \u0026micro;W m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e K\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e.\u003csup\u003e4\u003c/sup\u003e Despite these advancements, polymer-based materials still lag behind their inorganic counterparts, such as PbSe crystals, which boast a record power factor of approximately 10,000 \u0026micro;W m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e K\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and average \u003cem\u003ezT\u003c/em\u003e of 1.5 at 300 K\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u003c/sup\u003e. Recent progress\u003csup\u003e\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e has seen the development of polymer films with periodic heterogeneous structures, achieving a power factor of 347 \u0026micro;W m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e K\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e at 298 K and a peak \u003cem\u003ezT\u003c/em\u003e of approximately 1.28 at 368 K. This achievement underscore the potential of organic semiconductor polymers for efficient energy conversion. However, a significant performance gap remains, necessitating strategic advancements to enhance the thermoelectric performance of semiconductor polymers by refining their microstructure.\u003c/p\u003e \u003cp\u003eThe efficiency of thermoelectric materials, as quantified by the figure of merit \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:zT=\\frac{{S}^{2}\\sigma\\:}{\\kappa\\:}\\)\u003c/span\u003e\u003c/span\u003e, hinges on optimizing electrical conductivity (\u003cem\u003eσ\u003c/em\u003e) and the Seebeck coefficient (\u003cem\u003eS\u003c/em\u003e) in conjunction with thermal conductivity (\u003cem\u003eκ\u003c/em\u003e). The inherently low \u003cem\u003eκ\u003c/em\u003e in conducting polymers places emphasis on the power factor (\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{PF=S}^{2}\\sigma\\:\\)\u003c/span\u003e\u003c/span\u003e), directing research towards enhancing \u003cem\u003eσ\u003c/em\u003e and \u003cem\u003eS\u003c/em\u003e simultaneously. Achieving this, however, is challenging due to the inverse relationship between \u003cem\u003eσ\u003c/em\u003e and \u003cem\u003eS\u003c/em\u003e with increased charge density (\u003cem\u003en\u003c/em\u003e). A promising approach involves improving mobility while maintaining constant carrier concentration, thereby circumventing the inherent trade-off between \u003cem\u003eσ\u003c/em\u003e and \u003cem\u003eS\u003c/em\u003e\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e,\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eFor conjugated polymers, increasing crystallinity is a key strategy to enhance carrier mobility, as it promotes long-range order and facilitates efficient charge transport\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e\u003c/sup\u003e. This approach has been successfully applied in the development of high-performance thermoelectric polymers, particularly in semicrystalline polymers derived from polythiophenes and donor-acceptor (D-A) copolymers\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e. These materials exhibit high crystallinity, which enables efficient charge transport and high power factors through meticulous molecular design\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e,\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e. However, validating these molecular designs can be time-consuming and labor-intensive due to the complexities involved in polymer synthesis.\u003c/p\u003e \u003cp\u003eTo address these challenges, alternative approaches such as polymer chain alignment have emerged. By reimagining solution processing techniques, researchers have achieved significant improvements in thermoelectric performance\u003csup\u003e\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e,\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e,\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e. For example, a record power factor of 2900 \u0026micro;W m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e K\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e was achieved in a polythiophene system through mechanical rubbing to align polymer chains\u003csup\u003e\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e\u003c/sup\u003e. Yet, this alignment tactic introduces anisotropic transport in polymer films, complicating the design of thermoelectric devices for real-world applications. Moreover, high crystallinity along the chain alignment direction often leads to increased thermal conductivity, which can diminish thermoelectric efficiency as dictated by the Wiedemann-Franz law\u003csup\u003e\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e. Given these challenges, exploring alternative yet simple methods to create systems with superior crystallinity for polymer thermoelectrics is of significant interest.\u003c/p\u003e \u003cp\u003eNucleating agents are widely employed in traditional polymer industry to control crystallization kinetics and optimize the solid-state microstructures of bulk polymers\u003csup\u003e\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e\u003c/sup\u003e. These agents, including macromolecular additives like carbon nanotubes\u003csup\u003e\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e, graphene\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e, and thiophene-containing copolymers\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e, have been effectively used to modify crystallization processes and improve the morphology of thin films, thereby enhancing targeted properties. More recently, supramolecular nucleating agents\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e have emerged as transformative additives, capable of dissolving uniformly in polymer melts at high temperatures and self-assembling into structured nanoarchitectures upon cooling. These agents can significantly enhance carrier mobilities in semicrystalline polymers like P3DDT\u003csup\u003e\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e\u003c/sup\u003e and P3HT\u003csup\u003e\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e by up to 40-fold. Integrating such additives into doped semicrystalline polymers could be a promising approach to enhance their thermoelectric properties. However, several challenges remain, particularly whether the addition of nucleating agents will improve crystallinity and if the enhanced crystallinity introduced by the nucleating agent can be preserved during doping without compromising doping efficiency. To advance high-performance thermoelectric polymers using this strategy, it is essential to gain a comprehensive understanding of the interaction between nucleating agents and chemical doping, particularly its impact on microstructural evolution and charge transport within the nucleating agent-integrated polymer system.\u003c/p\u003e \u003cp\u003eIn the present study, we focus on Poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT), a thiophene-based semiconducting polymer renowned for its ordered microstructures and high charge carrier mobility\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e, as a foundational model system. We simply blend PBTTT-C14 with the nucleating agent N,N'-(1,4-phenyl)diisonicotinamide (PDA), targeting enhanced charge transport and thermoelectric properties. PBTTT's resilience to sequential doping allows it to maintain a high degree of structural order at high doping levels\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e\u003c/sup\u003e, making it an ideal platform to explore the intricate interplay between structural morphology, charge transport, and thermoelectric performance. Our findings reveal that PDA markedly optimizes the crystallization behavior of PBTTT-C14, as substantiated by techniques like differential scanning calorimetry (DSC), atomic force microscopy (AFM) and grazing incidence wide-angle X-ray scattering (GIWAXS). The subsequent doping via the ion exchange (IEx) method amplifies these traits, leading to notable advancements in the electrical conductivity and thermoelectric properties.\u003c/p\u003e \u003cp\u003eNotably, incorporating just 0.9 wt% PDA into PBTTT-C14 films minimizes structural disorder, demonstrating remarkable resilience to IEx doping, and achieving a high electrical conductivity of 1800 S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e alongside a maximum power factor approximating 150 \u0026micro;W m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e K\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, surpassing that of doped, pristine PBTTT-C14 films (σ\u003csub\u003emax\u003c/sub\u003e\u0026thinsp;~\u0026thinsp;878 S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and PF\u003csub\u003emax\u003c/sub\u003e ~ 31 \u0026micro;W m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e K\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e). We provide a comprehensive analysis of the mechanisms underlying this significant enhancement in charge transport and thermoelectric performance, drawing upon optical spectroscopy, thermal analysis, microstructural characterization, and transport measurements. This study highlights the strategic integration of nucleating agents as a simple approach to advance thermoelectric polymers, potentially revolutionizing the field of polymer-based thermoelectric materials for advanced scientific applications.\u003c/p\u003e"},{"header":"2. Results and Discussion","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1. Incorporating A Nucleating Agent to Achieve Enhanced Crystallinity in Pristine PBTTT-C14 Films\u003c/h2\u003e \u003cp\u003eAs highlighted earlier, the key objective of this study is to systematically regulate the crystallinity of a model semicrystalline polymer, specifically PBTTT-C14, to elucidate the complex relationship between microstructure, morphology, charge carrier transport, and thermoelectric performance, particularly under chemical doping conditions. Prior to the sequential IEx doping process, we firstly fine-tune the crystallinity of pristine polymer films, which are spin-coated from blending solutions with varying concentrations of the nucleating agent (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea; and see Experimental Section for details). We selected PDA, a supramolecular nucleating agent known for its remarkable ability to enhance the crystallinity of chemically similar polymer, such as Poly(3-hexylthiophene) (P3HT), with just 0.1 wt% loading\u003csup\u003e20\u003c/sup\u003e. Impressively, PDA significantly improves the crystallinity and crystalline domain size of PBTTT-C14, as corroborated by DSC, GIWAXS, and AFM. The results of these characterizations are discussed in detail below.\u003c/p\u003e \u003cp\u003eWe conducted a series of DSC experiments on PBTTT-C14/PDA blended samples, varying additive concentrations ranging from 0 wt% to 3.4 wt%, to probe the impact of nucleating agents on the crystallization kinetics of the polymer. All samples exhibit two primary thermal transitions (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb): a low-temperature transition (Transition I) occurring below 100 ℃, and a high-temperature transition (Transition II) centered around 220 ℃, which is characteristic of PBTTT's thermal behavior\u003csup\u003e\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e\u003c/sup\u003e. The effect of nucleating agents on Transition I is less pronounced, as indicated by the cooling curves in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb. Notably, the calorimetric peak corresponding to Transition II exhibits distinct variations with increasing PDA concentrations. Therefore, our further investigations focus on film samples annealed above the T\u003csub\u003ec\u003c/sub\u003e of Transition II, specifically the ribbon phase regime.\u003c/p\u003e \u003cp\u003eThe addition of PDA progressively raises the crystallization temperature (T\u003csub\u003ec\u003c/sub\u003e) of PBTTT-C14, reaching 226.33 ℃ at a 0.9 wt% concentration, an increase of 3.04 ℃. Beyond this concentration, higher PDA loadings resulted in a decline in T\u003csub\u003ec\u003c/sub\u003e. This initial shift in T\u003csub\u003ec\u003c/sub\u003e to higher temperatures at low additive loadings, up to 0.9 wt%, suggests heterogeneous nucleation, which enhances the polymer's crystallization capacity\u003csup\u003e\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e. The substantial improvement in crystallinity for these blended samples is directly evidenced by the increase in the enthalpy of crystallization (ΔH), a parameter proportional to the degree of crystallinity\u003csup\u003e\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e\u003c/sup\u003e. Specifically, the sample with 0.9 wt% PDA exhibited a ΔH peak of 16.69 J/g at transition II (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec), representing a 45% increase compared to pristine PBTTT films. However, at higher PDA concentrations, the degree of crystallinity declined, as evident by notable reductions in both T\u003csub\u003ec\u003c/sub\u003e and ΔH. This reduction in crystallinity can be attributed to the overloading of the nucleating agent. Overuse of nucleating agents might lead to an excessively high nucleation rate, resulting in the formation of numerous small and imperfect crystalline grains. This high nucleation rate impedes further crystal growth, ultimately leading to a decrease in overall crystallinity\u003csup\u003e\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eGIWAXS analysis was employed to investigate the evolution of crystalline order in pristine PBTTT-C14 and PBTTT-C14/PDA blended films across various nucleating agent concentrations. Both pristine and blended films exhibit high crystallinity, characterized by four orders of (h00) diffraction peaks along the \u003cem\u003eq\u003c/em\u003e\u003csub\u003e\u003cem\u003ez\u003c/em\u003e\u003c/sub\u003e axis, representing the lamellar stacking direction, and two additional peaks at 1.45 \u0026Aring;\u003csup\u003e\u0026minus;1\u003c/sup\u003e and 1.71 \u0026Aring;\u003csup\u003e\u0026minus;1\u003c/sup\u003e on the \u003cem\u003eq\u003c/em\u003e\u003csub\u003e\u003cem\u003exy\u003c/em\u003e\u003c/sub\u003e axis, corresponding to the polymer backbone and π-stacking orientation, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed-f; and Figure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e in the Supporting Information). Overall, the 2D GIWAXS scattering patterns reveal a remarkable similarity between the samples, with enhanced diffraction intensities along the in-plane \u003cem\u003eq\u003c/em\u003e\u003csub\u003e\u003cem\u003exy\u003c/em\u003e\u003c/sub\u003e directions for the film containing 0.9 wt% of the nucleating agent. To further explore the molecular stacking behavior upon the incoporation of the nucleating agent, we analyzed the 1D line-cut scattering profiles (Figure \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e) and extracted crystallographic parameters, summarized in Table \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e. For the film with 0.9 wt% PDA, no notable changes in paracrystallinity (\u003cem\u003eg\u003c/em\u003e\u003csub\u003e\u003cem\u003eπ\u0026minus;π\u003c/em\u003e\u003c/sub\u003e) and higher coherence length (\u003cem\u003eL\u003c/em\u003e\u003csub\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sub\u003e) were observed. These observations suggest that while there is a significant enhancement in crystallinity, the molecular stacking behavior of PBTTT-C14 is largely preserved up to an optimal concentration of PDA.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe morphological changes in the polymer films due to the addition of PDA were examined using AFM. The height image in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eg shows that the pristine PBTTT-C14 thin film, annealed at 260 ℃, exhibits uniform ribbons-like structures with an average width of 53.18 nm, a characteristic feature of films annealed from a smectic, liquid crystalline phase (Transition II)\u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e\u003c/sup\u003e. These ribbons consist of crystalline domains that maintain a smectic chain arrangement, typically comprising multiple chain-extended or chain-folded polymer chains, depending on the degree of chain alignment in the solid state\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e. Upon the initial incorporation of PDA, the ribbon structure was preserved, with the ribbon width increasing by 62%, from 53 nm in the pristine film to 86 nm at 0.9 wt% nucleating agent, indicating a tendency for aggregation. However, at a higher PDA concentration of 3.4 wt%, the ribbon width decreased to 42 nm. This transformation is accompanied by the gradual blurring of the nanofibrillar structure, suggesting a loss of long-range fiber periodicity (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ei; and Figure S3 in the Supporting Information). These observations imply that the addition of PDA at low concentrations (up to 0.9 wt%) enhances the degree of crystallinity and promotes the growth of individual ribbons, which is crucial for improving both structural order and charge transport. The observation of enlarged crystalline domains (ribbons) coupled with narrower grain boundaries at an optimal PDA loading suggests that the PBTTT-C14/PDA blended system may serve as a viable platform for subsequent doping and thermoelectric property investigations. Such a highly ordered microstructural morphology is anticipated to facilitate both efficient intradomain and interdomain charge transport.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2. Preserving Superior Structural Order in PBTTT-C14/PDA Blended Films upon Ion Exchange Doping\u003c/h2\u003e \u003cp\u003eChemical doping plays a pivotal role in modulating the electronic and thermoelectric properties of polymer semiconductors, effectively adjusting the energy level and optimizing the charge concentration \u003cem\u003en.\u003c/em\u003e\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e However, achieving optimal thermoelectric conversion in a polymer system often necessitates a charge concentration n surpassing 10\u003csup\u003e19\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e, which may significantly disturb the molecular packing within the neat polymer matrix, potentially compromising the high carrier mobility \u003cem\u003e\u0026micro;\u003c/em\u003e derived from its high crystalline order\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e. To harness the enhanced crystallinity of PBTTT-C14 films induced by the nucleating agent for enhancing thermoelectric performance, we adopted a newly developed IEx doping method. This doping technique has exhibited remarkable efficacy in achieving doping concentrations exceeding 10\u003csup\u003e20\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e, while imparting minimal or even positive effects on the microstructure and morphology of the polymer films. This preservation of superior structural order is critical for maintaining efficient charge transport. The successful achievement of efficient doping and preservation of superior structural order in PBTTT-C14/PDA blended films was confirmed through spectroscopic, GIWAXS, and AFM characterizations (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e and Figure S2, S4 in the Supporting Information).\u003c/p\u003e \u003cp\u003eThe extent of doping in all polymer films, with varying PDA concentrations, both before and after IEx doping, was evaluated using Ultraviolet-Visible-Near Infrared (UV-Vis-NIR) spectroscopy. For all the blended films studied, the neutral π-π\u003csup\u003e*\u003c/sup\u003e band centered around 550 nm exhibited nearly complete bleaching (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ea; and Figure S5 in the Supporting Information), a trend consistent with the pristine PBTTT film (Figure S5). Simultaneously, two broad absorption bands, labelled P1 and P2, appeared at wavelengths \u0026gt; 2000 nm and around 800 nm, respectively. These absorption bands are indicative of polaron or multi-polaron states, as commonly observed in highly doped PBTTT films\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e,\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e. These UV-Vis-NIR absorption profiles suggest the blended films obtained at high doping levels comparable to those of pristine PBTTT-C14, with a doping concentration around 10\u003csup\u003e21\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e, corresponding to roughly one charge per monomer unit. This high carrier density, confirmed for both pristine and blended systems, is further validated by Hall effect analysis presented in Section \u003cspan refid=\"Sec7\" class=\"InternalRef\"\u003e4\u003c/span\u003e of the Supporting Information.\u003c/p\u003e \u003cp\u003eFourier Transform Infrared Spectroscopy (FT-IR) was employed to investigate the degree of polaron delocalization in doped films (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eb). Polaron delocalization can be effectively assessed by examining polaron-induced absorption features in the mid-infrared (mid-IR) region\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e,\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e. Upon doping, the P1 band peaks around 1800 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e with a weak shoulder below 1500 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, corresponding to intrachain and interchain transitions, respectively\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e. Additionally, a number of narrow peaks are superimposed between 400 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1475 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which are typically interpreted as infrared active vibrational modes (IRAVs). The intensity of the IRAVs is an indicator of the extent of polaron delocalization along the polymer chains and between chains. The more intense the IRAVs, the greater the degree of polaron delocalization\u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e. In the FT-IR spectra of the doped blended films, the pronounced IRAV peaks suggest that a high level of polaron delocalization was achieved via ion exchange doping, similar to that observed in pristine PBTTT-C14 films\u003csup\u003e\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e,\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eGIWAXS characterization was employed to examine the microstructural changes in both pristine PBTTT-C14 and PBTTT-C14/PDA blended films after IEx doping. As depicted in the 2D diffraction patterns in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed-f, all doped films retain their lamellar packing, featuring an edge-on orientation of the polymer backbone and considerable long-range crystallinity. Both the well-ordered out-of-plane peaks (h00) and in-plane stacking peaks remain clearly visible, resembling their undoped counterparts. Upon IEx doping, the lamellar spacing notably expands for both the pristine and blended films, for instance, from 20.937 \u0026Aring; to 26.449 \u0026Aring; for the 0.9 wt% blended sample. This expansion suggests that the counterions predominantly integrate into the alkyl side-chain regions, consistent with previous findings on semicrystalline polythiophenes\u003csup\u003e\u003cspan additionalcitationids=\"CR37\" citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e. Interestingly, a reduction in the π-π stacking distance is observed across all samples: in the pristine film, this distance decreases from 3.601 \u0026Aring; to 3.526 \u0026Aring; (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ed; and Table S2 in the Supporting Information), while in the 0.9 wt% and 3.4 wt% blended films, it reduces from 3.646 \u0026Aring; to 3.516 \u0026Aring; and from 3.654 \u0026Aring; to 3.524 \u0026Aring;, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003ee-f; and Table S2 in the Supporting Information). This reduction can be attributed to the strengthening of polaronic coupling between chains, facilitated by the IEx doping process\u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e. Furthermore, all three films display a\u0026thinsp;~\u0026thinsp;10% decrease in paracrystallinity parameter (g\u003csub\u003eπ\u0026minus;π\u003c/sub\u003e) compared to their undoped states, suggesting that ion exchange doping effectively enhances structural order without causing discernible disruption, even in the presence of nucleating agent additives (Table S2 in the Supporting Information). The high electrical conductivities of both the pristine and blended systems, with σ\u003csub\u003emax\u003c/sub\u003e ranging from 878 to 1800 S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, are strongly correlated with reduced paracrystalline disorder, in line with previous findings in high-mobility semicrystalline polymers and donor-acceptor copolymers\u003csup\u003e\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eIt is important to note the differences in charge transport and thermoelectric properties between the pristine and blended systems. In particular, the doped 0.9 wt% blended system achieves a conductivity of approximately 1800 S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and an exceptional thermoelectric power factor of about 150 \u0026micro;W m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e K\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e (as disscussed in Section \u003cspan refid=\"Sec5\" class=\"InternalRef\"\u003e2.3\u003c/span\u003e and 2.4). These remarable enhancements cannot be solely attributed to molecular packing, as there are no significant differences in paracrystallinity and coherence length between doped pristine PBTTT film and 0.9 wt% blended film (Table S2 in Supporting Information). Instead, the enhanced thermoelectric performance in the blended systems can be primarily linked to a notable increase in crystallinity, as demonstrated through detailed microstructural and morphological analyses of the undoped counterparts.\u003c/p\u003e \u003cp\u003eIn conclusion, the GIWAXS analysis reveals that the counterions primarily occupy the side-chain regions, while IEx doping enhances backbone planarization, promoting efficient charge transport in all doped films\u0026mdash;especially in the 0.9 wt% PBTTT-C14/PDA blended system. Overall, the introduction of the nucleating agent into PBTTT-C14 does not significantly interfere with the IEx doping process, enabling highly effective doping while maintaining or even improving the superior crystalline order.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3. Thermoelectric Properties of Ion Exchange Doped PBTTT-C14/PDA Blended Films\u003c/h2\u003e \u003cp\u003eWe now turn our attention to the thermoelectric performance of the ion exchange (IEx) doped PBTTT-C14/PDA blended films. As shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea and \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eb, the electrical conductivity (σ) and Seebeck coefficient (S) of these doped polymers exhibit distinct trends as a function of PDA concentration, ranging from 0 wt% to 3.4 wt%.\u003c/p\u003e \u003cp\u003eSpecifically, Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ea shows a significant increase in electrical conductivity, reaching a peak value of 1178 S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e at 0.9 wt% PDA loading with a doping concentration of 3 mM. This represents an 85% enhancement compared to the conductivity of the doped pristine PBTTT-C14 film under the same doping conditions. This improvement is consistent with the crystallinity evolution with PDA concentration, as discussed in Section \u003cspan refid=\"Sec3\" class=\"InternalRef\"\u003e2.1\u003c/span\u003e. Notably, the Seebeck coefficient follows a similar trend, decoupling from the electrical conductivity. The doped 0.9 wt% blended film exhibits a maximum Seebeck coefficient of approximately 36 \u0026micro;V K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, which is 148% higher than that of the doped pristine film. As a result, the power factor (PF) of the doped 0.9 wt% blended film attains an impressive 150 \u0026micro;W m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e K\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, representing a remarkable 1011% improvement over the pristine film at an equivalent doping concentration, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec.\u003c/p\u003e \u003cp\u003eThe inset of Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ec further emphasizes the competitive advantage of our IEx doped 0.9 wt% blended system when compared to other unaligned benchmark systems, achieved through morphology control\u003csup\u003e\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e\u003c/sup\u003e, doping engineering\u003csup\u003e\u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e,\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e\u003c/sup\u003e. Remarkably, this optimal performance is on par with a recently developed highly oriented PBTTT system\u003csup\u003e\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e, which, despite requiring complex processing techniques\u0026mdash;such as controlled tie chain incorporation through polymer blending coupled with large-scale alignment\u0026mdash;results in notable charge transport anisotropy. The simultaneous increase in both σ and S, leading to a substantial enhancement in the PF with the appropriate PDA additive loading, is unprecedented. The detailed mechanisms underlying this phenomenon are elaborated in Section 2.4.\u003c/p\u003e \u003cp\u003eTo further fine-tune the thermoelectric performance of the 0.9 wt% blended system, we optimized the S and σ as a function of doping concentration. For comparison, the same experiment was performed on a pristine PBTTT-C14 system to better understand the impact of PDA additives on thermoelectric properties. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ed, the electrical conductivity initially increases with rising doping concentration, peaking at approximately 7 mM for the doped 0.9 wt% blended system. At this concentration, the blended film achieves an electrical conductivity of 1800 S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, more than double the maximum conductivity of 878 S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e observed in the doped pristine system at a doping concentration of 12.5 mM. In terms of the Seebeck coefficient, both the blended and pristine systems exhibit a comparable downward trend with increasing doping concentration. Consequently, the calculated power factors are presented in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef. Notably, the ion exchange doped PBTTT-C14/PDA blended films reach a significantly higher maximum power factor of 150 \u0026micro;W m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e K\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, far surpassing the 31 \u0026micro;W m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e K\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e achieved by the doped pristine counterpart.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThese findings underscore the promising potential of nucleating agent additive engineering in significantly enhancing the thermoelectric performance of high-performance semicrystalline conjugated polymers. A comparative analysis of the thermoelectric properties between blended and pristine systems reveals that the remarkable PF achieved by the IEx doped PBTTT-C14/PDA blend (0.9 wt%) is primarily driven by its exceptional charge transport properties. To further investigate, we explored the charge transport physics to uncover the fundamental mechanisms by which the nucleating agent facilitates improved charge transport in the doped PBTTT systems.\u003c/p\u003e \u003cp\u003e \u003cb\u003e2.4. Mechanisms Underlying the Remarkable Enhancement in Charge Transport and Thermoelectric Performance of IEx Doped PBTTT-C14/PDA Blended Films\u003c/b\u003e \u003c/p\u003e \u003cp\u003eCharge transport measurements are essential for characterizing transport parameters in semiconducting materials, allowing for the correlation between microscopic spatial and energetic distributions through microstructural characterization and charge transport models\u003csup\u003e\u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e\u003c/sup\u003e. For doped polymer semiconductors, temperature-dependent measurements of electrical conductivity, the Seebeck coefficient, and the Hall coefficient provide insight into the dominant transport mechanisms\u0026mdash;whether they involve localization (hopping-like) or delocalization (metal-like)\u0026mdash;that govern electronic transport\u003csup\u003e\u003cspan additionalcitationids=\"CR45\" citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e\u003c/sup\u003e. In this study, we applied this experimental framework to investigate how the incorporation of a nucleating agent additive affects charge transport physics and the microstructural characteristics of PBTTT-C14 films subjected to sequential ion exchange doping.\u003c/p\u003e \u003cp\u003eFigure \u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ea depicts the temperature (T) dependence of electrical conductivity for both pristine and blended films doped at a concentration of 5 mM, highlighting the significant effect of PDA concentration. Across all systems the temperature dependence of conductivity reflects that of high conductivity PBTTT, characterized by a plateau or slight decrease above 250 K, particularly prominent in the 0.9 wt% blended system. The appearance of a conductivity peak suggests a shift toward metallic conduction rather than thermally activated hopping conduction, especially at grain boundaries\u003csup\u003e\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e. To quantify the thermal activation energy (E\u003csub\u003ea\u003c/sub\u003e) governing each sample's conductivity, we applied the Arrhenius equation (see Supporting Information Section 5). The E\u003csub\u003ea\u003c/sub\u003e, which reflects energetic disorder within integer charge transfer complex (ICTC) states\u003csup\u003e\u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e\u003c/sup\u003e, decreases from 3.25 meV in pristine PBTTT to 2.67 meV at 0.9 wt% PDA loading, where conductivity peaks (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb, upper panel). This minimal E\u003csub\u003ea\u003c/sub\u003e in the 0.9 wt% blended sample signifies the lowest energetic disorder, which can be attributed to optimal crystallinity and structural ordering (Sections \u003cspan refid=\"Sec3\" class=\"InternalRef\"\u003e2.1\u003c/span\u003e \u0026amp; \u003cspan refid=\"Sec5\" class=\"InternalRef\"\u003e2.3\u003c/span\u003e). As a result, the 0.9 wt% blended film achieves a peak charge carrier mobility of 2.92 cm\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e V\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, confirmed by Hall effect measurements (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee).\u003c/p\u003e \u003cp\u003eAdditionally, by fitting the Seebeck coefficient-conductivity (S-σ) data using the Kang-Snyder model\u003csup\u003e\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e\u003c/sup\u003e (see the Supporting Information Section 6 for more details), we derived the energy barrier for charge percolation between ordered domains, denoted as W\u003csub\u003eγ\u003c/sub\u003e. Unlike E\u003csub\u003ea\u003c/sub\u003e, which provides insights into the overall transport mechanism encompassing both intra- and inter-domain transport, W\u003csub\u003eγ\u003c/sub\u003e specifically offers insights into inter-domain transport, providing a macroscopic perspective on conductivity across crystalline regions\u003csup\u003e\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e,\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e\u003c/sup\u003e. W\u003csub\u003eγ\u003c/sub\u003e follows a trend similar to E\u003csub\u003ea\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb, bottom panel), reaching its minimum at intermediate PDA concentrations before slightly increasing at higher concentrations, likely due to decreased overall crystallinity from excessive PDA loadings, as observed in DSC, GIWAXS, and AFM data discussed earlier. Notably, the decreasing ratio of W\u003csub\u003eγ\u003c/sub\u003e to E\u003csub\u003ea\u003c/sub\u003e with increasing PDA concentration (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ec) suggests that inter-domain energetic disorder plays a diminished role in limiting conductivity and carrier mobility.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo further investigate the synergistic impact of nucleating agent additive engineering and IEx doping on the charge transport properties of PBTTT-C14, we conducted comparative analyses of the S-σ relationship (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed) across varying doping concentrations for both pristine and 0.9 wt% blended systems. By applying the Kang-Snyder model to the S-σ relationship, we observe that a single parameter set (s and σ\u003csub\u003eE0\u003c/sub\u003e) inadequately describes the entire conductivity range (See the Supporting Information Section 6 for more details). Notably, both systems exhibit a distinct change in charge transport characteristics around 200 S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, transitioning from s\u0026thinsp;=\u0026thinsp;3 to s\u0026thinsp;=\u0026thinsp;1 with increasing conductivity. This transition is generally indicative of an insulator-to-metal transition occurring in semicrystalline polymer systems, particularly when carrier densities exceed 10\u003csup\u003e21\u003c/sup\u003e cm\u003csup\u003e\u0026minus;\u0026thinsp;3 40,\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003eIn both the 's\u0026thinsp;=\u0026thinsp;3' and 's\u0026thinsp;=\u0026thinsp;1' regimes, the 0.9 wt% blended system demonstrates notably higher σ\u003csub\u003eE0\u003c/sub\u003e values, specifically 0.03 S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 120 S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, respectively, which are approximately more than 2 times greater than those of the pristine system. Since σ\u003csub\u003eE0\u003c/sub\u003e acts as a weighted mobility factor tied to intrinsic carrier mobility\u003csup\u003e\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e,\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e\u003c/sup\u003e, this observation highlight the enhanced charge transport capability of the doped 0.9 wt% blended system. This superiority is further evidenced by the consistently higher Hall mobility measurements across the entire conductivity spectrum (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee). Consequently, the 0.9 wt% blended system exhibits significantly improved electrical conductivity for a given Seebeck coefficient, resulting in a substantially higher PF.\u003c/p\u003e \u003cp\u003eA comprehensive correlation analysis between transport measurements and microstructural characterization data allowed us to formulate a physical model (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ef) that elucidates the mechanism behind the enhanced charge transport properties induced by the nucleating agent additive. Upon incorporating an optimal concentration (0.9 wt%) of PDA, PBTTT-C14 films experience a significant increase in crystallinity, as demonstrated by DSC analysis. This increase is accompanied by improved structural order at the grain boundaries without disrupting the crystalline lattices within the domains. The polymer chain extension, supported by AFM and GIWAXS characterizations, contributes to this enhanced structural order. Such improvements are preserved, and in some cases intensified, across a broad range of carrier concentrations through ion exchange doping (Section \u003cspan refid=\"Sec4\" class=\"InternalRef\"\u003e2.2\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eRecent experimental and theoretical investigations have underscored structural disorder, rather than Coulombic trapping, as the primary determinant limiting charge transport in doped polymers, especially at high doping levels\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e,\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e\u003c/sup\u003e. This explains the superior carrier mobility of the doped 0.9 wt% blended system, which achieves substantially higher electrical conductivities compared to the unblended system when sufficient charge densities are introduced. Specifically, the chain extension reduces grain boundary sizes and promotes the formation of tie chains that bridge adjacent crystalline domains by clustering together. This enables charge carriers to traverse domains without relying on interchain hopping through disordered regions. This dual effect\u0026mdash;grain boundary size reduction and tie chain formation\u0026mdash;significantly alleviates energetic disorder at grain boundaries, as evidenced by the substantial decreases in the activation energies E\u003csub\u003ea\u003c/sub\u003e and the transport energy barriers W\u003csub\u003eγ\u003c/sub\u003e. The macroscopic resistance of the 0.9 wt% system is therefore reduced, with grain boundary resistance often being a major limiting factor for conductivity in many polymer semiconductors\u003csup\u003e\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e,\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e\u003c/sup\u003e. Additionally, the enhanced crystalline order within domains after IEx doping, indicated by reduced g\u003csub\u003eπ\u0026minus;π\u003c/sub\u003e values, fosters intradomain charge transport, promoting two-dimensional charge carrier delocalization. This further reduces the overall energetic disorder and lowers E\u003csub\u003ea\u003c/sub\u003e.\u003c/p\u003e \u003cp\u003eThis synergistic improvement in both intra- and inter-domain charge transport, stemming from nucleating agent additive engineering and ion-exchange doping, results in a record-high electrical conductivity of approximately 1800 S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and an outstanding thermoelectric performance, with a PF of 150 \u0026micro;W m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e K\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e for PBTTT-C14 films.\u003c/p\u003e \u003c/div\u003e"},{"header":"3. Conclusion","content":"\u003cp\u003eIn summary, we propose a straightforward yet highly effective conceptual approach that utilizes nucleating agents to precisely control the crystallization behavior of semicrystalline polymer semiconductors, thus thermoelectric performance. This method presents a clear pathway to enhance charge transport and achieve outstanding thermoelectric performance by increasing the degree of crystallinity without compromising the molecular packing order, while also improving electrical connectivity within doped polymer films. Through meticulous assessment of microstructural evolution driven by nucleating agents and IEx doping, we identified 0.9 wt% as the optimal PDA loading for achieving superior structural ordering. Remarkably, this ordering remains robust, even slightly improving after doping. As a result, structural disorder is minimized, and charge carrier mobility is maximized in highly doped PBTTT-C14 films, leading to exceptional transport properties, including a Hall mobility of up to 2.92 cm\u003csup\u003e\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e\u003c/sup\u003e V\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e s\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, electrical conductivity reaching 1800 S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e, and a power factor close to 150 \u0026micro;W m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e K\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e. Our approach breaks through the conventional barriers limiting the thermoelectric performance of polymer semiconductors by significantly boosting conductivity without reducing the Seebeck coefficient. This enhancement is primarily due to the reduction in grain boundary size facilitated by nucleating agent engineering, coupled with a modest increase in crystalline order within domains, further amplified by IEx doping. Importantly, this methodology holds broad applicability across various semicrystalline polymers, potentially driving significant advances in fast charge transport in highly doped conjugated polymers, ultimately contributing to the development of high-performance thermoelectric materials for next-generation organic electronics.\u003c/p\u003e"},{"header":"4. Experimental Section","content":"\u003cp\u003e \u003cb\u003eSample Preparation\u003c/b\u003e:\u003c/p\u003e \u003cp\u003e \u003cstrong\u003eMaterials\u003c/strong\u003e \u003cp\u003ePoly(2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT-C14) was purchased from Sigma-Aldrich. N,N'-(1,4-phenylene)diisonicotinamide (PDA, \u0026gt;\u0026thinsp;97% purity), acetonitrile (ACN, \u0026gt;\u0026thinsp;99.9% purity, water content\u0026thinsp;\u0026lt;\u0026thinsp;30 ppm), and 1,2-dichlorobenzene (DCB, \u0026gt;\u0026thinsp;98% purity, water content\u0026thinsp;\u0026lt;\u0026thinsp;50 ppm) were sourced from Adamas. Iron(III) chloride (FeCl\u003csub\u003e3\u003c/sub\u003e, \u0026gt;\u0026thinsp;99.99% purity) and 1-Butyl-1-Methylpyrrolidinium Bis(trifluoromethylsulfonyl)imide (BMP-TFSI, \u0026gt;\u0026thinsp;99% purity, water content\u0026thinsp;\u0026lt;\u0026thinsp;0.04%) were obtained from Aladdin. All reagents were used as received, without further purification.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eBlend solution preparation\u003c/strong\u003e \u003cp\u003ePBTTT-C14 was dissolved in DCB at a concentration of 10 g/L, with heating to 110\u0026deg;C and stirring for 2 hours, followed by filtration through a 0.22 \u0026micro;m PTFE membrane. PDA was dispersed in DCB at 1 g/L with 2 hours of stirring. Defined volumes of PBTTT-C14 and PDA solutions were mixed, and the mixture was heated and stirred at 110\u0026deg;C for an additional hour.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eDopant solution preparation\u003c/strong\u003e \u003cp\u003eBMP-TFSI solutions were prepared in ACN at concentrations of 250, 500, 750, 1000, and 1500 mM, and FeCl\u003csub\u003e3\u003c/sub\u003e solutions were prepared in ACN at concentrations of 2.5, 5, 7.5, 10, and 15 mM. Dopant mixtures were obtained by combining appropriate volumes of BMP-TFSI and FeCl\u003csub\u003e3\u003c/sub\u003e solutions (e.g., 250 mM BMP-TFSI solution with 2.5 mM FeCl\u003csub\u003e3\u003c/sub\u003e solution can be configured to produce a 0.25 mM mixed dopant solution). The mixed dopant solution concentration was set to 0.25, 0.5, 0.75, 1, 3, 5, 7, 10, 12.5 mM. The FeCl\u003csub\u003e3\u003c/sub\u003e solutions were freshly prepared before use. All solutions were prepared in an argon-filled glove box (\u0026lt;\u0026thinsp;1 ppm H\u003csub\u003e2\u003c/sub\u003eO and O\u003csub\u003e2\u003c/sub\u003e).\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eThin film preparation\u003c/b\u003e: The solutions were spin-coated onto preheated substrates at 1500 rpm for 60 seconds using preheated pipettes. Following deposition, films were annealed at 260\u0026deg;C for 20 minutes and cooled at a controlled rate of 2\u0026deg;C/min to room temperature to promote the formation of a ribbon phase. For doping, 150 \u0026micro;L cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e of dopant solution was applied to the films, left for 60 seconds, and then the excess solution was removed by spin-coating at 7000 rpm for 60 seconds. Afterward, the films were rinsed with acetonitrile to eliminate residual dopants. For electrical measurements, a protective layer of Cytop was spin-coated onto the films using a diluted Cytop solution (Cytop:solvent\u0026thinsp;=\u0026thinsp;1:2) at 2000 rpm for 60 seconds. All procedures were carried out in an argon-filled glove box.\u003c/p\u003e \u003cp\u003e \u003cb\u003eSample Preparation for Characterization\u003c/b\u003e:\u003c/p\u003e \u003cp\u003e \u003cstrong\u003eElectrical and seebeck measurements\u003c/strong\u003e \u003cp\u003eSamples were fabricated on 13 mm \u0026times; 6 mm glass substrates with 10 nm-thick gold electrodes (1.5 mm wide).\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eHall effect measurements\u003c/strong\u003e \u003cp\u003eSamples were prepared on 10 mm \u0026times; 10 mm glass substrates with 2 mm \u0026times; 2 mm gold electrodes deposited at the corners.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eGIWAXS samples\u003c/strong\u003e \u003cp\u003ePrepared on 10 mm \u0026times; 10 mm silicon substrates.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eUV-Vis and FTIR samples\u003c/strong\u003e \u003cp\u003ePrepared on glass substrates of comparable dimensions.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eCharacterization Methods\u003c/b\u003e:\u003c/p\u003e \u003cp\u003e \u003cstrong\u003eDifferential scanning calorimentry (DSC)\u003c/strong\u003e \u003cp\u003ePBTTT-C14/PDA samples were analyzed using a TA Discovery25 under nitrogen. Samples were annealed at 280\u0026deg;C for 5 minutes and cooled at 10\u0026deg;C/min to -80\u0026deg;C.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eConductivity and Seebeck Coefficient Measurements\u003c/strong\u003e \u003cp\u003eConductivity and Seebeck coefficient were measured using a ULVAC-RIKO ZEM-3 system under helium. Film thickness was determined by AFM (Bruker Dimension Icon), and conductivity was measured via the four-probe method. Seebeck coefficients were obtained through the linear fitting of ΔV vs. ΔT.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eUltraviolet-Visible-Near Infrared Spectroscopy (UV-Vis-NIR)\u003c/strong\u003e \u003cp\u003eSpectra were recorded using a Lambda365 instrument over a range of 250\u0026ndash;2500 nm with 2 nm intervals. Substrate background spectra were collected separately as the baseline.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eFourier-transform infrared spectroscopy (FTIR)\u003c/b\u003e: FTIR spectra were obtained on a Bruker Vertex 70 spectrometer over the 400\u0026ndash;4000 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e range, with a 4 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e interval. \u003cb\u003eAtomic force microscopy (AFM)\u003c/b\u003e: Tapping-mode AFM was conducted on a Bruker Dimension Icon system to characterize the surface morphology. The ribbon width was determined by averaging measurements from at least thirty randomly selected ribbons.\u003c/p\u003e \u003cp\u003e \u003cstrong\u003eGrazing incidence wide angle X-ray scattering (GIWAXS)\u003c/strong\u003e \u003cp\u003eMeasurements were performed using the Xenocs Xeuss 3.0 system with an 8.04 keV X-ray source and an EIGER2 detector positioned 80 mm from the sample. Data were recorded with a 0.18\u0026deg; incident angle and analyzed using GIWAXS-Tools software. Coherence length and paracrystallinity were calculated using convolution Gaussian and Lorentzian fittings\u003csup\u003e\u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e\u003c/sup\u003e (see Section \u003cspan refid=\"Sec1\" class=\"InternalRef\"\u003e1\u003c/span\u003e in the Supporting Information for more details).\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eHall effect Measurement\u003c/strong\u003e \u003cp\u003eHall measurements were performed on an ET9000 Hall instrument modified with the reverse field reciprocity theorem\u003csup\u003e\u003cspan additionalcitationids=\"CR56\" citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e\u003c/sup\u003e. The setup included Keithley 6220, 2182A, and 6485 instruments, achieving 10 fA current and 1 nV voltage resolutions. Measurements were conducted with a 1000 nA current and a magnetic field of 18 kG. Film thicknesses were measured by AFM.\u003c/p\u003e \u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eACKNOWLEDGMENT\u003c/h2\u003e \u003cp\u003eWe acknowledge support from the National Natural Science Foundation of China (52273029, 52203022), Fujian Science \u0026amp; Technology Innovation Laboratory for Optoelectronic Information of China (2021ZZ119), the Pilot Project of Fujian Province (2022H0037), Fuzhou Technology Innovation Platform (2022-P-020), Natural Science Foundation of Fujian Province for Distinguished Young Scholars (2023J06045), and Fujian\u0026ndash; CAS joint STS Project (2023T3064). C.C. acknowledges support from the Hunan Provincial Natural Science Foundation of China (2022JJ40547), and the University of Defense Technology Research Project (ZK22-15).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eRuss B, Glaudell A, Urban JJ, Chabinyc ML, Segalman RA (2016) Organic thermoelectric materials for energy harvesting and temperature control. Nat Rev Mater 1\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang SH, Zuo GZ, Kim J, Sirringhaus H (2022) Progress of Conjugated Polymers as Emerging Thermoelectric Materials. 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Adv Funct Mater 34:202400255. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003e10.1002/adfm.202400255\u003c/span\u003e\u003cspan address=\"10.1002/adfm.202400255\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-5136690/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5136690/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eNucleating agents are widely recognized for their ability to refine the solid-state morphology and microstructure of semi-crystalline polymers, significantly influencing their physicochemical properties. This study presents a simple yet effective strategy to dramatically improve the thermoelectric properties of semi-crystalline polymer films. By blending less than 1 wt% of the nucleating agent N,N'-(1,4-phenyl)diisonicotinamide (PDA) into Poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT-C14), we induce a controlled modulation of crystallization behavior, resulting in optimized microstructures with reduced structural disorder and improved charge carrier mobility. Systematic analysis of varying PDA concentrations identifies an optimal loading of 0.9 wt%, which yields a remarkable 45% increase in crystallinity relative to pristine PBTTT films. Under optimized doping conditions, the doped PBTTT-C14 film with 0.9 wt% PDA exhibits an exceptional electrical conductivity of 1800 S cm\u003csup\u003e\u0026minus;\u003c/sup\u003e\u0026sup1; and an optimal power factor of 150 \u0026micro;W m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e K\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, representing 105% and 384% improvements, respectively, over the doped pristine PBTTT-C14 film. These enhancements are primarily due to the synergistic effects of polymer chain extension and reduction of grain boundary size, which together mitigate grain boundary resistance and improve charge transport efficiency. Furthermore, the study elucidates the role of ion exchange doping in maintaining a high density of charge carriers without compromising the crystalline structure introduced by PDA. This research not only deepens the understanding of polymer thermoelectrics but also sets the stage for the development of innovative materials that could transform energy conversion technologies and polymer-based electronic devices.\u003c/p\u003e","manuscriptTitle":"Remarkable Enhancement of Thermoelectric Performance of Semicrystalline Polymer Films upon Incorporating A Nucleating Agent Additive","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-10-09 07:52:53","doi":"10.21203/rs.3.rs-5136690/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"422b7ca3-c892-4092-9cd1-bbc73bcc1630","owner":[],"postedDate":"October 9th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":38612221,"name":"Physical sciences/Materials science/Soft materials/Polymers"},{"id":38612222,"name":"Physical sciences/Materials science/Materials for energy and catalysis/Thermoelectrics"}],"tags":[],"updatedAt":"2024-11-08T10:10:59+00:00","versionOfRecord":[],"versionCreatedAt":"2024-10-09 07:52:53","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-5136690","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5136690","identity":"rs-5136690","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}