Heteroatom engineering enhancing thermoelectric power factor of molecular junctions

Heteroatom engineering enhancing thermoelectric power factor of molecular junctions | 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 Heteroatom engineering enhancing thermoelectric power factor of molecular junctions Yuan Li, Wuxian Peng, Ningyue Chen, Yu Xie, Liang Ma, Jingtao Lü This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4763672/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 Engineering power factor (PF) of molecular junctions is one of the most attractive research in the field of thermoelectronics for the applications in thermal management and high-performance thermoelectric energy conversion at the nanoscale. Here, we modified the chemical structure of self-assembled monolayers (SAMs) formed by the widely investigated alkanethiolate (C n -SH, n = 5, 8, 11, 14) through heteroatom substitutions, including the terminal iodine (I) atom substitution and replacing backbone methylene units (-CH 2 -) with oxygen (O) atoms, to obtain iodo-substituted oligo(ethylene glycol) thiolates (I-(C 2 O) m -C 2 -SH, m = 1, 2, 3, 4). We carried out the electrical tunneling and thermoelectric measurements based on the eutectic Ga-In technique (EGaIn) and found that the electrical conductance ( G ) and Seebeck coefficient ( S ) of the SAMs with I-(C 2 O) m -C 2 -SH can be enhanced simultaneously compared to the length-matched SAMs of C n -SH (n = 3m + 2), resulting in the PF of I-(C 2 O) 4 -C 2 -SH being over 5 orders of magnitude higher than that of C 14 -SH, which was attributed to the resonant states contributed from the substituted I-(C 2 O) m -C 2 -SH near the Fermi energy. This study underscored the significance of chemically engineering the organic molecules to dramatically boost PF of molecular junctions for the further applications of high-efficient nanoscale thermoelectric devices. Physical sciences/Energy science and technology/Thermoelectric devices and materials Physical sciences/Materials science/Nanoscale materials/Molecular self-assembly Thermoelectric effects Power factor Self-assembled monolayer Heteroatom substitution Tunnelling Figures Figure 1 Figure 2 Figure 3 Introduction Molecule-based thermoelectric devices have the potential to revolutionize energy generation and cooling at the nanoscale. 1–9 These devices convert waste heat into electricity, and their efficiency is determined by a critical parameter known as the power factor (PF = S 2 G , where S is the Seebeck coefficient or thermopower, G is the electrical conductance). The PF is a measure of how much electricity can be generated under applied temperature difference ( ΔT ) and depends on various transport properties of thermoelectric materials. 10,11 In bulk materials, the enhanced thermopower often leads to the decreased conductivity ( σ ), resulting in an optimal value of PF. However, in molecular junctions, the discrete energy levels near Fermi energy allows for the simultaneous increase in thermopower and electrical conductance, leading to a promisingly high PF. 12 It has been demonstrated that the values of PF for alkanethiolates were about two-fold higher than length-matched conjugated molecular wire (higher in conductance in general, for instance benzenethiol, biphenyl-4-thiol and terphenyl-4-thiol) 13 . While the reported PF of self-assembled monolayers (SAM)-based molecular junctions, for example, 10 − 11 to 10 − 10 µW m − 1 K − 2 for octane-1-thiol, 10,13 were remarkably lower than the theoretical values as proposed by Gotsmann et al. 14 (at least 10 3 µW m − 1 K − 2 ). Therefore, despite the theoretical prediction of promising molecular thermoelectric junctions according to the Landauer theory, significant research efforts need to be taken for a better performance. 15 Here, we investigated S , G and related PF across the SAMs of saturated n-alkyl derivatives with a properly molecular structure engineering approach by selected substitutes of O and I atoms. The PF of the individual molecule was found to exceed 10 − 7 µW m − 1 K − 2 , which over three orders of magnitude larger than the reported values. Since the thermal conductivity of polyehthylene glycol (PEG) is 0.2–0.5 W m − 1 K − 1 , 16−18 our molecular design with a similar backbone to PEG could point towards a highly promising value of figure of merit. In addition, our atomically precise engineering of thermoelectric properties showed that the molecules could hold great potential for high-efficiency heat-to-charge conversion and cooling elements of CMOS-based nanoscale devices. In pursuing larger values of PF in molecular junctions, molecules do not seem to follow the theoretical prediction well. Recently, Reddy et al . 8 demonstrated that the expected large S and G of the porphytins derivatives was not supported by the experimental findings due to the HOMO-1 of porphytin moieties not following the theoretical estimation to participate in charge transport. Agraït et al . 19 introduced Blatter radical molecules with intrinsic spin states into molecular junctions and merely enhanced the related PF by one order of magnitude. The molecular junctions of endohedral metallofullerenes 20 and organometallic complexes 21 are predicted to possess promisingly high PF. However, their experimental PF were smaller than 100 fW/K − 2 and 4×10 − 19 W/K − 2 , respectively. The destructive and constructive quantum interference effects are essential methods to control the charge transport and thermoelectric properties in molecular junctions, while the increased S is usually accompanied by the declined G , and vice versa, leading to the ineffective improvement of PF. 22–25 According to previous investigations, S and G can be enhanced via replacing alkyl with oligo(ethylene glycol) as the backbone for the mechanism of charge transport changing from off-resonant tunneling to superexchange coupling assisted direct tunneling. 26,27 While the reason why superexchange coupling can increase S and how to control molecule-electrode coupling to enhance PF have not been clearly elucidated. Therefore, the main focus of this paper is to engineer molecules, including substitutions of backbone and terminal groups, to tune the tunneling barrier and the coupling strength between the SAMs and the top electrode and to explain variation trends of S , G and PF. Indeed, improving the PF of molecular junctions remains a challenge. To attain high PF, a more promising approach is to simultaneously engineer both the charge transport channel from the backbone and the interface from the terminal group of the molecules. It is accepted that G is proportional to transmission function ( τ ( E ), E denotes the molecular energy levels) of electron tunneling at Fermi level ( E F ) of the electrode and S is adversely proportional to its slope. In order to obtain higher PF, we can regulate the relative position between the frontier molecular orbitals ( E FMO ) and E F or introduce resonant states into molecular junctions (Fig. 1 a). In this work, thiol was utilized as the anchor group for all molecules to form the densely packed SAMs. By terminal I atom substitution and replacing backbone methylene units (-CH 2 -) with O atom, we systematically analyzed how these substitutions affected the location of energy levels, interactions between the SAMs and the top electrode (the liquid metal of Gallium/Indium alloy, EGaIn), as well as the mechanism of charge transport across molecular junctions of thiol-based derivatives: alkanethiolates (C n -SH (n = 5, 8, 11, 14)), iodo-substituted alkanethiolates (I-C n -SH (n = 5, 8, 11, 14)), oligo(ethylene glycol) thiolates ((C 2 O) m -C 2 -SH (m = 2, 3, 4), n = 3m + 2) and iodo-substituted oligo(ethylene glycol) thiolates (I-(C 2 O) m -C 2 -SH (m = 1, 2, 3, 4)) (Fig. 1 b). The data of C 8 -SH in this study is in accordance with our previous work. 13 The synthetic processes of the compounds were shown in Supporting Information Section of Synthesis (Fig. S1 ~ S54). Figure 1 c depicts the thermoelectric molecular junctions with the SAMs of C 14 -SH, which could be regarded as a tunneling barrier that increased with longer molecular length. The thermoelectric junction for the SAMs of I-(C 2 O) 4 -C 2 -SH was illustrated in Fig. 1 d, where the O atoms in the backbone provided delocalized molecular orbitals 26 and the I atoms in the terminal groups could reduce the contact resistance between the SAMs and the EGaIn electrode by 5-times 28 , all of which resulted in the declined electron tunneling barrier and altering the electron transfer mechanism from coherent tunneling to superexchange tunneling. We showed that the values of S and G of alkylthiol-based complexes could be improved at the same time both for terminal I-substituted and backbone O-substituted saturated molecular wires. The main unexpected results were that the PF of the SAMs of I-(C 2 O) 4 -C 2 -SH was dramatically boosted by a factor of 8.5 \(\:\text{×}\) 10 5 comparing with the SAMs of C 14 -SH with approximately matched length, offering an effective strategy to atomically engineering of high-property thermoelectric molecular devices. Results and discussion Determination of G , S and related PF of the molecular junctions. All the SAMs were assembled on the template stripped Au (Au TS ) electrode and contacted with cone-shaped EGaIn electrode in accordance with our previous work. 29 The preparation of the Au TS electrode and the SAMs were set forth in Supporting Information Section S2 and the corresponding characterizations of the SAMs were summarized in Supporting Information Section S3, including X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). It could be obtained, according to the S 2 p spectra (Fig. S55 ~ S58), that all the SAMs readily formed dense monolayers on the Au TS electrode. The I 3 d spectra were ascribed to the terminal I atoms substitution. Based on UPS spectra, we could see that the energy offset ( δE ME ) between all the investigated SAMs and the bottom electrodes ranged from ~ 2.1 eV to ~ 2.4 eV and changed insignificantly, identifying that the SAMs possessed the very similar coupling strength between the SAMs and the Au TS electrode (Fig. S59 ~ 62, Table S1 ~ S4). To analyze how substitutions by I and O atoms affected the rate of electron tunneling across molecular junctions, we measured electrical characteristic curves of the SAMs with varied molecular lengths and averaged log 10 | J |− V plots are shown in Fig. 2 a and S63 (see Supporting Information Section S4 for details) (Here, J and V were the current density and the applied voltage). Figure S64 containes corresponding histograms of log 10 | J | at -0.5V. We made three important observations (Fig. 2 b): 1) the current density of the SAMs declined with longer molecular length, of which dropped by ~ 4 and ~ 2 orders of magnitude for the SAMs of C n -SH and I-Cn-SH, respectively, when varying n from 5 to 14; 2) the current density of I-(C 2 O) m -C 2 -SH only attenuated ~ 1 order of magnitude for increasing m from 1 to 4; 3) the value of tunnelling decay coefficient ( β ) for molecular junctions of C n -SH (n = 5, 8, 10, 11) was 0.85 similar to previous works 30 , and that of I-C n -SH(n = 5, 8, 10, 11) and (C 2 O) m -C 2 -SH (m = 2, 3, 4) were 0.36 and 0.25, respectively, according to the Simmons equations (Fig. 2 b). In addition, the conductivity ( σ ) (at + 0.1V) of I-C 11 -SH in this work was ~ 2 orders of magnitude larger than that of C 11 -SH, while Nijhuis reported enhancement of 3 orders of magnitude 31 and Whitesides showed that halogen atoms substitution modestly affect the current density 32 . The value of β for molecular junctions with I-(C 2 O) m -C 2 -SH (m = 1, 2, 3, 4) was 0.18 and indistinguishable from that of conjugated molecular wires, 33 indicating that the SAMs we prepared were densely packed with few defects. What’s more, the current density at -0.5V of I-(C 2 O) 4 -C 2 -SH was ~ 4 orders magnitude higher than that of length-matched C 14 -SH (Fig. 2 a and S63), indicating the tunneling barrier was largely reduced by I atoms and O atoms substitutions. Table 1 Parameters used to calculate PF for molecular junctions with C n -SH, I-C n -SH, (C 2 O) m -C 2 -SH, I-(C 2 O) m -C 2 - SH. Molecule l (Å) a l J (+ 0.1V)l (A cm − 2 ) b ε (GVm − 1 ) c \(\:\sigma\:\) (µS cm − 1 ) d S (µV K − 1 ) e PF (10 − 10 µW m − 1 K − 2 ) f C 5 -SH 5.78 0.25 0.173 0.144 6.6 ± 0.5 6.27 C 8 -SH 9.02 0.02 0.110 0.017 4.8 ± 0.1 0.39 C 11 -SH 12.38 9.33×10 − 4 0.081 1.115×10 − 3 4.5 ± 0.3 2.26×10 − 2 C 14 -SH 15.66 4.06×10 − 5 0.064 6.343×10 − 5 2.8 ± 0.1 4.97×10 − 4 I-C 5 -SH 7.23 0.66 0.138 0.478 10.8 ± 0.4 55.75 I-C 8 -SH 10.68 0.11 0.094 0.120 9.2 ± 0.4 10.17 I-C 11 -SH 13.83 0.03 0.072 0.042 5.8 ± 0.2 1.41 I-C 14 -SH 17.20 8.91×10 − 3 0.058 0.015 2.8 ± 0.1 0.12 (C 2 O) 2 -C 2 -SH 8.51 0.15 0.118 0.130 5.8 ± 0.2 4.37 (C 2 O) 3 -C 2 -SH 11.63 0.05 0.086 0.058 4.2 ± 0.1 1.02 (C 2 O) 4 -C 2 -SH 14.65 0.02 0.068 0.029 3.7 ± 0.1 0.40 I-C 2 O-C 2 -SH 7.08 24.00 0.141 17.021 10.8 ± 0.4 2.00×10 3 I-(C 2 O) 2 -C 2 -SH 10.21 12.88 0.098 13.143 11.2 ± 0.3 1.64×10 3 I-(C 2 O) 3 -C 2 -SH 13.26 4.37 0.075 5.827 11.1 ± 0.5 7.18×10 2 I-(C 2 O) 4 -C 2 -SH 16.37 2.10 0.061 3.423 11.1 ± 0.5 4.22×10 2 a l represents the molecular length determined by ChemDraw software considering the tilt angle (30°). b Determined from J - V curves in Fig. 2 a and S63. c ε is the magnitude of electric field intensity and is obtained from the applied voltage across the junctions (+ 0.1 V) devided by l . d \(\:\sigma\:\) is the conductivity of the SAMs and is obtained as \(\:\sigma\:\) = J / ε . e The significant digit of S is 0.1 µV/K based on the accuracy of the output voltage and the accuracy of the input temperature and was detailed discussed in our previous work. 13 f It is difficult to directly estimate the error bar of PF, since the values of PF are calculated from S and σ . Therefore, we utilized the average of S and σ to obtain PF of the SAMs, and we have noticed that other groups also only reported the error of S and σ but not PF. 7,8,10,34 To characterize S of molecular junctions, we recorded potential difference ( ΔV ) in response of temperature difference ( ΔT = 2.0 K, 3.5 K, 5.0 K) applied on the SAMs with heating the bottom Au TS electrode and cooling the top EGaIn electrode. The corresponding setup and analysis protocol of thermoelectric measurements was reported by our previous study as shown in Fig. S65 (see Supporting Information Section S5 for details). 13 Here, we give a brief description. For each SAM at applied ΔT , we measured at least 20 junctions to generate statistical significant data to determine average of ΔV () and related standard-deviation by Gaussians fitting (Fig. S66 ~ 70). Then, the values of S for molecular junctions can be obtained by plotting as a function of ΔT (Fig. 2 c and S71). After detailed analysis of dependence between measured and S (reported in our previous work), we acquired the values of S for the SAMs as listed in Table 1 . We observed: 1) the positive sign of S for the investigated molecules indicated HOMO dominated charge transport properties in all cases; 2) engineering molecules by terminal I atom substitution and replacing backbone -CH 2 - unite with O atom could result in the enhanced values of S comparing with C n -SH; 3) S for the SAMs of C n -SH, I-C n -SH and (C 2 O) m -C 2 -SH declined with increased molecular length; 4) the values of S for the SAMs of I-(C 2 O) m -C 2 -SH, ~ 11 µV/K, were nearly independent on molecular length, and that of I-(C 2 O) 4 -C 2 -SH was ~ 4 times higher than C 14 -SH (Fig. 2 d). Therefore, combining these substitutions could enhance the Seebeck coefficient of the SAMs, which is a crucial step toward enhancing the thermoelectric performance of molecular junctions. To evaluate the enhancement of the thermoelectric effect, we calculated the values of PF of each SAM (Fig. 2 e and Table 1 ) and the detailed processes were reported in Supporting Information Section S5. It is interesting that values of log 10 PF linearly attenuated with the molecular length, which has not been reported before. We think the reasons could be 1) terminal I atom substitution and replacing backbone methylene units (-CH 2 -) by O atom improved the current density ranging from 2 to 4 orders of magnitude and the measured log 10 | J | followed a good linear correlation with molecular length, 2) the increase of S by the atomically tuned chemical structures was less than 5 times and the sharply promoted PF was mainly originated for the change of G , resulting in the calculated PF being basically linearly related to the molecular length. The values of PF enhanced by 1–2 orders of magnitude through I atoms substitution, so does backbone O atom substitution. When m = 1 for I-(C 2 O) m -C 2 -SH, its PF improved by ~ 3 orders of magnitude compared with C 5 -SH. The longer the molecular length, the greater of degree of improvement. The PF of I-(C 2 O) 4 -C 2 -SH was ~ 8.5 \(\:\text{×}\) 10 5 times higher that of C 14 -SH, demonstrating our molecular design could dramatically boosted PF of the SAMs. As reported by Agraït 19 and Lambert 35 , the occurrence of resonant states in τ ( E ) near E F could bring enhancement both for S and G . Therefore, we proposed that the molecular engineering in this work not only increased SAMs/EGaIn electrode coupling, reducing barrier of electron tunneling, but also modified mechanism of charge transport from coherent tunneling to superexchange tunneling via lone-pair electrons on O atoms. Under synergistic effect of these substitutions, the molecular energy levels of I-(C 2 O) m -C 2 -SH resonated with E F of electrodes, which resulted in the simultaneously enhanced S and G and approximately 6 orders of magnitude improvement of PF for I-(C 2 O) 4 -C 2 -SH compared with C 14 -SH. Theoretical estimation of G , S and PF of the molecular junctions. To gain a deeper insight into the above mentioned results that atomically precise engineering of the organic molecules could improve S and G , we carried out theoretical transport calculations for the molecular junctions with C n -SH and I-(C 2 O) m -C 2 -SH as shown in Fig. 3 . The electronic structure calculations were performed at the DFT level using SIESTA 36 . The transmission spectra of molecular junctions were calculated using the non-equilibrium Green’s function (NEGF) method implemented in TRANSIESTA 37,38 . Afterwards, the linear response scheme was adopted to obtain the thermoelectric coefficients. 39–42 The G , S and PF can be written as follows: $$\:\:\:\:\:\:\:\:G(\mu\:,\:T)={\left.\frac{I}{{\Delta\:}V}\right|}_{\varDelta\:T=0}={e}^{2}{L}_{0}$$ 1 $$\:S(\mu\:,\:T)={\left.-\frac{{\Delta\:}V}{{\Delta\:}T}\right|}_{I=0}=-\frac{1}{eT}\frac{{L}_{1}}{{L}_{0}}$$ 2 $$\:\text{P}\text{F}=G{S}^{2}$$ 3 Here the coefficient L n is dependent on the transmission coefficient. $$\:{L}_{n}(\mu\:,\:T)=\frac{1}{h}{\int\:}_{-\infty\:}^{\infty\:}{\left(E-\mu\:\right)}^{n}T\left(E\right)(-\frac{\partial\:f(E,\mu\:,T)}{\partial\:E})dE$$ 4 The optimized structure of molecular junctions of C n -SH and I-(C 2 O) m -C 2 -SH are shown in Fig. 3 a and S72 ~ S73, where we utilized Au as the top electrode and use a constant self-energy to avoid the complication in modeling the EGaIn electrode, which has been done previously 43–45 . The molecule together with one extra layer of Au from each side were fully relaxed until the forces acting on each atoms were less than 0.02 eV/Å. The transmission coefficient of C n -SH gets lower as the molecular length increases as shown in Fig. 3 b and S74, which is the consequence of broader tunneling barriers for longer molecule. New resonances in the junctions formed by I-(C 2 O) m -C 2 -SH are found around E = -1.83 eV (as indicated by the black dashed line in Fig. 3 c). Since they ( E = -1.83 eV) are further away from the calculated Fermi energy ( E = 0 eV), their contribution to transport properties is negligible. However, in previous experimental studies signature of enhanced conductance due to these states were reported 44 . Several reasons may results in such discrepancy between theoretical and experimental results. One is that the standard DFT calculation is not accurate enough, especially in determining the Fermi level. The second could be that, the coupling between different molecules may lead to broadening these resonant states. To understand qualitatively the experimental results, we have chosen to take the Fermi energy as a tuning parameter. We have calculated the thermoelectric transport coefficients ( G , S and PF) using different Fermi energy values for C n -SH and I-(C 2 O) m -C 2 -SH, which are shown in Fig. S75 ~ S77. We find that only when the Fermi level is located near these resonant states, could the theoretical results be consistent with experimental ones (Fig. S78 ~ S79). We have shown theoretical results for E F = -1.83 eV in Fig. 3 . In this case, the improvement of both G and S for I-(C 2 O) m -C 2 -SH observed in the experiments can be reproduced from the DFT calculations (Fig. 3 d, e). We have the following observations (Fig. 3 f): 1) the values of PF for the SAMs of C n -SH gradually declined with the increased molecular length; 2) the PF of I-(C 2 O) m -SH were always higher than those of C n -SH for the equivalent molecular lengths; 3) the PF of I-(C 2 O) 4 -C 2 -SH was approximately 4 orders of magnitude larger than C 14 -SH. Therefore, the theoretical results offered a qualitative understanding of the experimental measurements, indicating that the molecular engineering method in this work could significantly increase the PF of molecular junctions, which is promising for further development of organic thermoelectric materials at nanoscale. In addition, the measured S of the SAMs of I-(C 2 O) m -C 2 -SH derivatives were much lower than the theoretically predicted values, highlighting that futher efforts should be devoted on the finely-tuning the electronic structures of molecular junctions to engineering the quantum transport properties for the high-performance thermoelectronic devices. In conclusion, we focused on how the heteroatom substitution, including the terminal I atom substitution and replacing the backbone -CH 2 - by O atoms, affected the charge transport across molecular junctions, and confirmed that both G and S could be improved in the SAMs of I-(C 2 O) m -C 2 -SH (m = 1, 2, 3, 4), compared to the length-matched C n -SH (n = 5, 8, 11, 14). According to the electrical tunneling results, the values of β for the SAMs of C n -SH and I-(C 2 O) m -C 2 -SH were 0.85 and 0.18, respectively, indicating the sharply declined tunneling barrier, and the value of σ (at + 0.1V) for I-(C 2 O) 4 -C 2 -SH was more than 4 orders of magnitude larger than that of C 14 -SH. In addition, the values of S for the SAMs of C n -SH, I-C n -SH and (C 2 O) m -SH declined with increased molecular length, while that for the SAMs of I-(C 2 O) m -C 2 -SH, ~ 11 µV/K, were nearly independent on molecular length. The S of I-(C 2 O) 4 -C 2 -SH was ~ 4 times higher than that of C 14 -SH. Therefore, the PF of I-(C 2 O) 4 -C 2 -SH was dramatically enhanced by a factor of 8.5 \(\:\text{×}\) 10 5 compering with C 14 -SH. Based on the DFT calculations, the underline mechanism was that the new resonances were introduced into the SAMs after heteroatom substitution near the Fermi energy. This work highlighted the importance of molecular engineering for nano thermoelectric devices with high-efficiency conversion of the wasted heat to the useful electricity. Methods All the experimental and theoretical data can be found in the supplemental information, including the synthetic processes of the compounds, the preparation of the Au TS electrode and the SAMs, the characterization of the SAMs, the electrical and thermoelectric measurement as well as the DFT calculation. Declarations Data availability The data that support the findings of this study are available within the article and its Supplementary Information files. All data underlying the findings of this work are available from the corresponding author upon request. Code availability The code used for the analyses is available from the corresponding authors on reasonable request. Competing interests The authors declare no competing interests. Author contributions Y. L. initiated the project and designed the experiments. W. P. synthesized the molecules. Y. X. prepared the bottom electrode. W. P. carried out electrical and thermoelectric measurements. N. C. performed surface characterization of SAMs, including XPS and UPS. L. M. and J. L. conducted DFT calculations. W. P., N. C., Y. L., L. M. and J. L. analyzed experimental data and contributed mainly to the writing of the manuscript. All authors discussed the results, data analysis, and contributed to the writing of the manuscript. Acknowledgements National Natural Science Foundation of China (22273045 and 62201494), Tsinghua University Independent Scientific Research Plan for Young Investigator, Tsinghua University Initiative Scientific Research Program and “Dushi” program. We also gratefully acknowledge NCESBJ (National Center of Electron Spectroscopy in Beijing) where the SAMs characterization was conducted. Additional information Supplementary information The online version contains supplementary material available at https://doi.org/xx.xxxx/xxxxxx-xxx-xxxxx-x. References Rincón-García, L., Evangeli, C., Rubio-Bollingera, G. & Agraït, N. Thermopower measurements in molecular junctions. Chem. Soc. Rev. 45 , 4285 ( 2016 ). Wang, K., Meyhofer, E. & Reddy, P. Thermal and thermoelectric properties of molecular junctions. Adv. Funct. Mater. 30 , 1904534 ( 2019 ). Yu‐Jia, Z. et al. Nanoscale Organic Thermoelectric Materials: Measurement, Theoretical Models, and Optimization Strategies. Adv. Funct. Mater. 30 , 1903873 ( 2019 ). Sohyun, P., Hungu, K. & Jae, Y. H. Structure–thermopower relationships in molecular thermoelectrics. J. Mater. Chem. A 7 , 14419 ( 2019 ). Cui, L. et al. Peltier cooling in molecular junctions. Nat. Nanotechnol. 13 , 122 ( 2018 ). Cui, L. et al. Thermal conductance of single-molecule junctions. Nature 572 , 628 ( 2019 ). Gehring, P. et al. Complete mapping of the thermoelectric properties of a single molecule. Nat. Nanotechnol. 16 , 426 ( 2021 ). Xu, H. et al. Electrical Conductance and Thermopower of β ‑Substituted Porphyrin Molecular Junctions-Synthesis and Transport. J. Am. Chem. Soc. 145 , 23541 ( 2023 ). Li, M. et al. Electrically gated molecular thermal switch. Science 382 , 585 ( 2023 ). Park, S., Kang, S. & Yoon, H. J. Power factor of one molecule thick films and length dependence. ACS Cent. Sci. 5 , 1975 ( 2019 ). Sowa, J. K., Mo, J. A. & Gauger, E. M. Marcus theory of thermoelectricity in molecular junctions. J. Phys. Chem. C . 123 , 4103 ( 2019 ). Chen, R., Lee, J., Lee, W. & Li, D. Thermoelectrics of Nanowires. Chem. Rev. 119 , 9260 ( 2019 ). Peng, W., Cao, Z., Chen, N., Xie, Y. & Li, Y. Dependence of thermoelectric effects in molecular junctions on the topography of the bottom electrodes. J. Mater. Chem. A 10 , 23304 ( 2022 ). Gemma, A. & Gotsmann, B. A roadmap for molecular thermoelectricity. Nat. Nanotechnol. 16 , 1299 ( 2021 ). Datta, S. Electronic transport in mesoscopic systems, Cambridge University, Cambridge, UK. Electronic transport in mesoscopic systems Cambridge University ( 1995 ). Mohaddespour, A., Abolghasemi, H., Mostaedi, M. T. & Habibzadeh, S. A new model for estimation of the thermal conductivity of polymer/clay nanocomposites. J. Appl. Polym. 118 , 1042 ( 2010 ). Ruan, K. & Gu, J. Ordered alignment of liquid crystalline graphene fluoride for significantly enhancing thermal conductivities of liquid crystalline polyimide composite films. Macromolecules 55 , 4134 ( 2022 ). Liua, Z., Wei, H., Tangb, B., Xuc, S. & Shufen, Z. Novel light–driven CF/PEG/SiO 2 composite phase change materials with high thermal conductivity. Sol. Energy Mater. 174 , 538 ( 2018 ). Hurtado-Gallego, J. et al. Thermoelectric enhancement in single organic radical molecules. Nano Lett. 22 , 948 ( 2022 ). Ismael, A. K. et al. Exploring seebeck-coefficient fluctuations in endohedral-fullerene, single-molecule junctions. Nanoscale Horiz. 7 , 616 ( 2022 ). Naher, M. et al. Molecular structure-(thermo)electric property relationships in single-molecule junctions and comparisons with single- and multiple-parameter models. J. Am. Chem. Soc. 143 , 3817 ( 2021 ). Wang, X. et al. Scale-up of room-temperature constructive quantum interference from single molecules to self-assembled molecular-electronic films. J. Am. Chem. Soc. 142 , 8555 ( 2020 ). Ismael, A. et al. Tuning the thermoelectrical properties of anthracene-based self-assembled monolayers. Chem. Sci. 11 , 6836 ( 2020 ). Jang, J., Jo, J. W., Ohto, T. & Yoon, H. J. Seebeck effect in molecular wires facilitating long-range transport. J. Am. Chem. Soc. 146 , 4922 ( 2024 ). Miao, R. et al. Influence of quantum interference on the thermoelectric properties of molecular junctions. Nano Lett. 18 , 5666 ( 2018 ). Baghbanzadeh, M. et al. Anomalously Rapid Tunneling: Charge Transport across Self-Assembled Monolayers of Oligo(ethylene glycol). J. Am. Chem. Soc. 139 , 7624 ( 2017 ). Cho, N. et al. Superexchange Coupling-Induced Enhancements of Thermoelectric Performance in Saturated Molecules. Nano Lett 21 , 360 ( 2021 ). Chen, X. et al. A single atom change turns insulating saturated wires into molecular conductors. Nat. Commun. 12 , 3432 ( 2021 ). Lin, J.-L. et al. Molecular diodes with tunable threshold voltage based on π‐extended tetrathiafulvalene. Adv. Mater. Interfaces 9 , 2201238 ( 2022 ). Li, Y., Jiang, L., Zhang, B. & Nijhuis, C. A. Dependency of the tunneling decay coefficient in molecular tunneling junctions on the topography of the bottom electrodes. Angew. Chem. Int. Edit. 53 , 3377 ( 2014 ). Wang, D. et al. Tuning the Tunneling Rate and Dielectric Response of SAM-Based Junctions via a Single Polarizable Atom. Adv. Mater. 27 , 6689 ( 2015 ). Baghbanzadeh, M., Pieters, P. F., Li, Y., Collison, D. & Whitesides, G. M. The rate of charge tunneling in EGaIn junctions is not sensitive to halogen substituents at the self-assembled monolayer//Ga 2 O 3 interface. ACS Nano 12 , 10221 ( 2018 ). Xie, Z., Bâldea, I., Smith, C. E., Wu, Y. & Frisbie, C. D. Experimental and theoretical analysis of nanotransport in oligophenylene dithiol junctions as a function of molecular length and contact work function. ACS Nano 8 , 8022 ( 2015 ). Rincón-García, L. et al. Molecular design and control of fullerene-based bi-thermoelectric materials. Nat. Mater. 15 , 289 ( 2016 ). Wang, K. et al. Charge transfer complexation boosts molecular conductance through Fermi level pinning. Chem. Sci. 10 , 2396 ( 2019 ). Soler, J. M. et al. The SIESTA method for ab initio order-N materials simulation. J. Phys.: Condens. Matter 14 , 2745 ( 2002 ). Brandbyg, M., Mozos, J.-L., Ordejón, P., Taylor, J. & Stokbro, K. Density-functional method for nonequilibrium electron transport. Phys. Rev. B 65 , 165401 ( 2002 ). Papior, N., Lorente, N., Frederiksen, T., García, A. & Brandbyge, M. Improvements on non-equilibrium and transport Green function techniques: The next-generation TRANSIESTA. Comput. Phys. Commun. 212 , 8 ( 2017 ). Bergfield, J. P. & Stafford, C. A. Thermoelectric signatures of coherent transport in single-molecule heterojunctions. Nano Lett. 9 , 3072 ( 2009 ). Ren, J., Zhu, J.-X., Gubernatis, J. E., Wang, C. & Li, B. Thermoelectric transport with electron-phonon coupling and electron-electron interaction in molecular junctions. Phys. Rev. B 85 , 155443 ( 2012 ). Bevilacqua, G., Grosso, G., Menichetti, G. & Parravicini, G. P. Thermoelectric efficiency of nanoscale devices in the linear regime. Phys. Rev. B 94 , 245419 ( 2016 ). Ma, L., Nian, L.-L. & Lü, J.-T. Design and optimization of a heat engine based on a porphyrin single-molecule junction with graphene electrodes. Phys. Rev. B 101 , 045410 ( 2020 ). Soni, S. et al. Understanding the role of parallel pathways via in-situ switching of quantum interference in molecular tunneling junctions. Angew. Chem. Int. Ed. 59 , 14308 ( 2020 ). Hu, Y. et al. Single dynamic covalent bond tailored responsive molecular junctions. Angew. Chem. Int. Ed. Engl. 60 , 20872 ( 2021 ). Kong, G. D., Byeon, S. E., Jang, J., Kim, J. W. & Yoon, H. J. Electronic mechanism of in situ inversion of rectification polarity in supramolecular engineered monolayer. J. Am. Chem. Soc. 144 , 7966 ( 2022 ). Additional Declarations There is NO Competing Interest. Supplementary Files SupportingInformation.docx Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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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-4763672","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":332343735,"identity":"c6a3c8b3-7e9a-4cc5-838a-0072daca33e7","order_by":0,"name":"Yuan Li","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABEElEQVRIiWNgGAWjYLCCBwYMDAYMzAdAJAgBARsBLQkGDBIGDGyJDSRoYQBp4TFsAHEIajG4kfzsQUIBQ525RM73hz8K7thtl0h+wPCh7DAD/+wGHFrSzA1ADrOckbuxmcfgWfLOGWkGjDPOHWaQuHMAh5YEMwmwX24AtTAYHE4Gihgw87YdZjCQSMChJf0bVEvOw8YfYC3pH5j/4tWSA7Mlh7GBx+CwHZBhwMyIR4vkmTdlIC2SG848M5wN1JJgcOZNwcGec+k8Ejewa+E7nr5N4sMfBn6D48kPPv74c9je4Hj6xgc/yqzl+Gdg16IACZX/cAFgfDIwgAR5sKoHAvkGNAF7XCpHwSgYBaNg5AIAWrhkOOqSHgsAAAAASUVORK5CYII=","orcid":"https://orcid.org/0000-0002-4204-2992","institution":"Tsinghua University","correspondingAuthor":true,"prefix":"","firstName":"Yuan","middleName":"","lastName":"Li","suffix":""},{"id":332343736,"identity":"42285aea-f0bf-41bd-89e2-0e87089075ab","order_by":1,"name":"Wuxian Peng","email":"","orcid":"","institution":"Tsinghua University","correspondingAuthor":false,"prefix":"","firstName":"Wuxian","middleName":"","lastName":"Peng","suffix":""},{"id":332343737,"identity":"e6bb5655-632c-456f-bddb-344bcc1fcbf2","order_by":2,"name":"Ningyue Chen","email":"","orcid":"","institution":"Tsinghua University","correspondingAuthor":false,"prefix":"","firstName":"Ningyue","middleName":"","lastName":"Chen","suffix":""},{"id":332343738,"identity":"1202ca6d-313e-4504-bfb0-e3b9eb70c75a","order_by":3,"name":"Yu Xie","email":"","orcid":"","institution":"Tsinghua University","correspondingAuthor":false,"prefix":"","firstName":"Yu","middleName":"","lastName":"Xie","suffix":""},{"id":332343739,"identity":"d6ca3ba0-790c-48bf-9ff2-53673e87d501","order_by":4,"name":"Liang Ma","email":"","orcid":"https://orcid.org/0000-0003-2407-9529","institution":"Yanshan University","correspondingAuthor":false,"prefix":"","firstName":"Liang","middleName":"","lastName":"Ma","suffix":""},{"id":332343740,"identity":"2d10e301-0199-4770-9fc1-5b645ab663a3","order_by":5,"name":"Jingtao Lü","email":"","orcid":"https://orcid.org/0000-0001-8518-2816","institution":"Huazhong University of Science and Technology","correspondingAuthor":false,"prefix":"","firstName":"Jingtao","middleName":"","lastName":"Lü","suffix":""}],"badges":[],"createdAt":"2024-07-18 15:30:41","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4763672/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4763672/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":61389040,"identity":"d32e434b-5f05-4cad-b77f-86aa972c215c","added_by":"auto","created_at":"2024-07-30 07:40:31","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":311032,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSchematic diagram of molecular junction.\u003c/strong\u003e (a) The principles of achiving larger \u003cem\u003eS\u003c/em\u003e, \u003cem\u003eG\u003c/em\u003e and PF in molecular junctions, including ① regulating the location of \u003cem\u003eE\u003c/em\u003e\u003csub\u003eFMO\u003c/sub\u003e and \u003cem\u003eE\u003c/em\u003e\u003csub\u003eF\u003c/sub\u003e and ② introducing resonance states into molecular junctions. (b) The design rules for molecules, including ① iodine atom substitution as functional group and ② the oligo (ethylene glycol) chain as backbone instead of the alkyl chain. (c) The molecular junctions based on alkanethiolates (C\u003csub\u003en\u003c/sub\u003e-SH, n = 5, 8, 11, 14), where molecules and EGaIn electrode are vdW interactions and charge transport mechanism is coherent tunneling. (d) The molecular junctions based on iodo-substituted oligo(ethylene glycol) thiolates (I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003em\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH(m = 1, 2, 3, 4), n = 3m + 2), where SAMs and EGaIn electrode exists strong coupling and charge transport mechanism is superexchange tunneling.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4763672/v1/98e5835273d6a3a8808d8019.png"},{"id":61389044,"identity":"5dae778a-2249-4311-bf7d-9952b1769a91","added_by":"auto","created_at":"2024-07-30 07:40:31","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":246534,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eDetermination of \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eG\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e, \u003c/strong\u003e\u003cem\u003e\u003cstrong\u003eS\u003c/strong\u003e\u003c/em\u003e\u003cstrong\u003e and PF of the molecular junctions.\u003c/strong\u003e (a) Average plots of the log\u003csub\u003e10\u003c/sub\u003e|\u003cem\u003eJ\u003c/em\u003e|−\u003cem\u003eV\u003c/em\u003e of C\u003csub\u003e14\u003c/sub\u003e-SH, I-C\u003csub\u003e14\u003c/sub\u003e-SH, (C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e4\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH and I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e4\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH. (b) Plots of log\u003csub\u003e10\u003c/sub\u003e|\u003cem\u003eσ\u003c/em\u003e| at +0.10 V versus number of non-hydrogen atoms. The solid lines are the linear fits to the experimental data. (c) Plots of thermoelectric voltage at applied Δ\u003cem\u003eT\u003c/em\u003e and the corrensponding histograms of \u0026lt;\u003cem\u003eΔV\u003c/em\u003e\u0026gt; with a Guassian fit to these histograms of C\u003csub\u003e14\u003c/sub\u003e-SH, I-C\u003csub\u003e14\u003c/sub\u003e-SH, (C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e4\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH and I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e4\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH. (d) Plots of \u003cem\u003eS\u003c/em\u003e \u003cem\u003evs\u003c/em\u003e number of non-hydrogen atoms for C\u003csub\u003en\u003c/sub\u003e-SH, I-C\u003csub\u003en\u003c/sub\u003e-SH, (C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003em\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH, I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003em\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH. (e) log\u003csub\u003e10\u003c/sub\u003ePF as a function of number of non-hydrogen atoms for C\u003csub\u003en\u003c/sub\u003e-SH (n = 5, 8, 11, 14), I-C\u003csub\u003en\u003c/sub\u003e-SH (n = 5, 8, 11,14), (C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003em\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH (m = 2, 3, 4), I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003em\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH (m = 1, 2, 3, 4).\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4763672/v1/8d0dc8123cfaa89428c67022.png"},{"id":61389041,"identity":"ea442235-513c-407f-afba-ea21cc8f8522","added_by":"auto","created_at":"2024-07-30 07:40:31","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":88210,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePF of the molecular junctions.\u003c/strong\u003e (a) The molecular junction configurations of C\u003csub\u003e14\u003c/sub\u003e-SH and I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e4\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH used in the theoretical calculation. The transmission coefficient \u003cem\u003eτ\u003c/em\u003e(\u003cem\u003eE\u003c/em\u003e) for (b) C\u003csub\u003en\u003c/sub\u003e-SH (n = 5, 8, 11, 14) and (c) I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003em\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH (m = 1, 2, 3, 4). The calculated (d) electrical conductance \u003cem\u003eG\u003c/em\u003e and (e) Seebeck coefficient \u003cem\u003eS\u003c/em\u003e at the \u003cem\u003eE\u003c/em\u003e = -1.83 eV (The black dashed lines in b and c). (f) The estimated PF based on the calculated \u003cem\u003eG\u003c/em\u003e and \u003cem\u003eS\u003c/em\u003e for the molecular junctions.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4763672/v1/eec7d7d9b3633b7eba323f46.png"},{"id":62776934,"identity":"35dbffd4-beab-4bd0-b9f8-8475bf3b4f07","added_by":"auto","created_at":"2024-08-19 10:48:25","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1490111,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4763672/v1/51eedc8b-3101-4c3e-828a-c5ebedc62aeb.pdf"},{"id":61389045,"identity":"8bf120d3-108d-4683-a4bb-d7b7655effd7","added_by":"auto","created_at":"2024-07-30 07:40:32","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":10590664,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cbr\u003e\u003c/p\u003e","description":"","filename":"SupportingInformation.docx","url":"https://assets-eu.researchsquare.com/files/rs-4763672/v1/f120dde701aeed64ae069133.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Heteroatom engineering enhancing thermoelectric power factor of molecular junctions","fulltext":[{"header":"Introduction","content":"\u003cp\u003eMolecule-based thermoelectric devices have the potential to revolutionize energy generation and cooling at the nanoscale.\u003csup\u003e1\u0026ndash;9\u003c/sup\u003e These devices convert waste heat into electricity, and their efficiency is determined by a critical parameter known as the power factor (PF\u0026thinsp;=\u0026thinsp;\u003cem\u003eS\u003c/em\u003e\u003csup\u003e2\u003c/sup\u003e\u003cem\u003eG\u003c/em\u003e, where \u003cem\u003eS\u003c/em\u003e is the Seebeck coefficient or thermopower, \u003cem\u003eG\u003c/em\u003e is the electrical conductance). The PF is a measure of how much electricity can be generated under applied temperature difference (\u003cem\u003eΔT\u003c/em\u003e) and depends on various transport properties of thermoelectric materials.\u003csup\u003e10,11\u003c/sup\u003e In bulk materials, the enhanced thermopower often leads to the decreased conductivity (\u003cem\u003eσ\u003c/em\u003e), resulting in an optimal value of PF. However, in molecular junctions, the discrete energy levels near Fermi energy allows for the simultaneous increase in thermopower and electrical conductance, leading to a promisingly high PF.\u003csup\u003e12\u003c/sup\u003e It has been demonstrated that the values of PF for alkanethiolates were about two-fold higher than length-matched conjugated molecular wire (higher in conductance in general, for instance benzenethiol, biphenyl-4-thiol and terphenyl-4-thiol) \u003csup\u003e13\u003c/sup\u003e. While the reported PF of self-assembled monolayers (SAM)-based molecular junctions, for example, 10\u003csup\u003e\u0026minus;\u0026thinsp;11\u003c/sup\u003e to 10\u003csup\u003e\u0026minus;\u0026thinsp;10\u003c/sup\u003e \u0026micro;W m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e K\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e for octane-1-thiol,\u003csup\u003e10,13\u003c/sup\u003e were remarkably lower than the theoretical values as proposed by Gotsmann \u003cem\u003eet al.\u003c/em\u003e\u003csup\u003e14\u003c/sup\u003e (at least 10\u003csup\u003e3\u003c/sup\u003e \u0026micro;W m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e K\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e). Therefore, despite the theoretical prediction of promising molecular thermoelectric junctions according to the Landauer theory, significant research efforts need to be taken for a better performance.\u003csup\u003e15\u003c/sup\u003e Here, we investigated \u003cem\u003eS\u003c/em\u003e, \u003cem\u003eG\u003c/em\u003e and related PF across the SAMs of saturated n-alkyl derivatives with a properly molecular structure engineering approach by selected substitutes of O and I atoms. The PF of the individual molecule was found to exceed 10\u003csup\u003e\u0026minus;\u0026thinsp;7\u003c/sup\u003e \u0026micro;W m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e K\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, which over three orders of magnitude larger than the reported values. Since the thermal conductivity of polyehthylene glycol (PEG) is 0.2\u0026ndash;0.5 W m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e,\u003csup\u003e16\u0026minus;18\u003c/sup\u003e our molecular design with a similar backbone to PEG could point towards a highly promising value of figure of merit. In addition, our atomically precise engineering of thermoelectric properties showed that the molecules could hold great potential for high-efficiency heat-to-charge conversion and cooling elements of CMOS-based nanoscale devices.\u003c/p\u003e \u003cp\u003eIn pursuing larger values of PF in molecular junctions, molecules do not seem to follow the theoretical prediction well. Recently, Reddy \u003cem\u003eet al\u003c/em\u003e.\u003csup\u003e8\u003c/sup\u003e demonstrated that the expected large \u003cem\u003eS\u003c/em\u003e and \u003cem\u003eG\u003c/em\u003e of the porphytins derivatives was not supported by the experimental findings due to the HOMO-1 of porphytin moieties not following the theoretical estimation to participate in charge transport. Agra\u0026iuml;t \u003cem\u003eet al\u003c/em\u003e.\u003csup\u003e19\u003c/sup\u003e introduced Blatter radical molecules with intrinsic spin states into molecular junctions and merely enhanced the related PF by one order of magnitude. The molecular junctions of endohedral metallofullerenes\u003csup\u003e20\u003c/sup\u003e and organometallic complexes\u003csup\u003e21\u003c/sup\u003e are predicted to possess promisingly high PF. However, their experimental PF were smaller than 100 fW/K\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e and 4\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;19\u003c/sup\u003e W/K\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e, respectively. The destructive and constructive quantum interference effects are essential methods to control the charge transport and thermoelectric properties in molecular junctions, while the increased \u003cem\u003eS\u003c/em\u003e is usually accompanied by the declined \u003cem\u003eG\u003c/em\u003e, and vice versa, leading to the ineffective improvement of PF.\u003csup\u003e22\u0026ndash;25\u003c/sup\u003e According to previous investigations, \u003cem\u003eS\u003c/em\u003e and \u003cem\u003eG\u003c/em\u003e can be enhanced via replacing alkyl with oligo(ethylene glycol) as the backbone for the mechanism of charge transport changing from off-resonant tunneling to superexchange coupling assisted direct tunneling.\u003csup\u003e26,27\u003c/sup\u003e While the reason why superexchange coupling can increase \u003cem\u003eS\u003c/em\u003e and how to control molecule-electrode coupling to enhance PF have not been clearly elucidated. Therefore, the main focus of this paper is to engineer molecules, including substitutions of backbone and terminal groups, to tune the tunneling barrier and the coupling strength between the SAMs and the top electrode and to explain variation trends of \u003cem\u003eS\u003c/em\u003e, \u003cem\u003eG\u003c/em\u003e and PF.\u003c/p\u003e \u003cp\u003eIndeed, improving the PF of molecular junctions remains a challenge. To attain high PF, a more promising approach is to simultaneously engineer both the charge transport channel from the backbone and the interface from the terminal group of the molecules. It is accepted that \u003cem\u003eG\u003c/em\u003e is proportional to transmission function (\u003cem\u003eτ\u003c/em\u003e(\u003cem\u003eE\u003c/em\u003e), \u003cem\u003eE\u003c/em\u003e denotes the molecular energy levels) of electron tunneling at Fermi level (\u003cem\u003eE\u003c/em\u003e\u003csub\u003eF\u003c/sub\u003e) of the electrode and \u003cem\u003eS\u003c/em\u003e is adversely proportional to its slope. In order to obtain higher PF, we can regulate the relative position between the frontier molecular orbitals (\u003cem\u003eE\u003c/em\u003e\u003csub\u003eFMO\u003c/sub\u003e) and \u003cem\u003eE\u003c/em\u003e\u003csub\u003eF\u003c/sub\u003e or introduce resonant states into molecular junctions (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea). In this work, thiol was utilized as the anchor group for all molecules to form the densely packed SAMs. By terminal I atom substitution and replacing backbone methylene units (-CH\u003csub\u003e2\u003c/sub\u003e-) with O atom, we systematically analyzed how these substitutions affected the location of energy levels, interactions between the SAMs and the top electrode (the liquid metal of Gallium/Indium alloy, EGaIn), as well as the mechanism of charge transport across molecular junctions of thiol-based derivatives: alkanethiolates (C\u003csub\u003en\u003c/sub\u003e-SH (n\u0026thinsp;=\u0026thinsp;5, 8, 11, 14)), iodo-substituted alkanethiolates (I-C\u003csub\u003en\u003c/sub\u003e-SH (n\u0026thinsp;=\u0026thinsp;5, 8, 11, 14)), oligo(ethylene glycol) thiolates ((C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003em\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH (m\u0026thinsp;=\u0026thinsp;2, 3, 4), n\u0026thinsp;=\u0026thinsp;3m\u0026thinsp;+\u0026thinsp;2) and iodo-substituted oligo(ethylene glycol) thiolates (I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003em\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH (m\u0026thinsp;=\u0026thinsp;1, 2, 3, 4)) (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eb). The data of C\u003csub\u003e8\u003c/sub\u003e-SH in this study is in accordance with our previous work.\u003csup\u003e13\u003c/sup\u003e The synthetic processes of the compounds were shown in Supporting Information Section of Synthesis (Fig. \u003cspan refid=\"MOESM1\" class=\"InternalRef\"\u003eS1\u003c/span\u003e\u0026thinsp;~\u0026thinsp;S54). Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec depicts the thermoelectric molecular junctions with the SAMs of C\u003csub\u003e14\u003c/sub\u003e-SH, which could be regarded as a tunneling barrier that increased with longer molecular length. The thermoelectric junction for the SAMs of I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e4\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH was illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ed, where the O atoms in the backbone provided delocalized molecular orbitals\u003csup\u003e26\u003c/sup\u003e and the I atoms in the terminal groups could reduce the contact resistance between the SAMs and the EGaIn electrode by 5-times\u003csup\u003e28\u003c/sup\u003e, all of which resulted in the declined electron tunneling barrier and altering the electron transfer mechanism from coherent tunneling to superexchange tunneling. We showed that the values of \u003cem\u003eS\u003c/em\u003e and \u003cem\u003eG\u003c/em\u003e of alkylthiol-based complexes could be improved at the same time both for terminal I-substituted and backbone O-substituted saturated molecular wires. The main unexpected results were that the PF of the SAMs of I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e4\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH was dramatically boosted by a factor of 8.5\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{\u0026times;}\\)\u003c/span\u003e\u003c/span\u003e10\u003csup\u003e5\u003c/sup\u003e comparing with the SAMs of C\u003csub\u003e14\u003c/sub\u003e-SH with approximately matched length, offering an effective strategy to atomically engineering of high-property thermoelectric molecular devices.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Results and discussion","content":"\u003cp\u003e\u003cstrong\u003eDetermination of\u003c/strong\u003e \u003cstrong\u003eG\u003c/strong\u003e, \u003cstrong\u003eS\u003c/strong\u003e \u003cstrong\u003eand related PF of the molecular junctions.\u003c/strong\u003e All the SAMs were assembled on the template stripped Au (Au\u003csup\u003eTS\u003c/sup\u003e) electrode and contacted with cone-shaped EGaIn electrode in accordance with our previous work.\u003csup\u003e29\u003c/sup\u003e The preparation of the Au\u003csup\u003eTS\u003c/sup\u003e electrode and the SAMs were set forth in Supporting Information Section S2 and the corresponding characterizations of the SAMs were summarized in Supporting Information Section S3, including X-ray photoelectron spectroscopy (XPS) and ultraviolet photoelectron spectroscopy (UPS). It could be obtained, according to the S 2\u003cem\u003ep\u003c/em\u003e spectra (Fig. S55\u0026thinsp;~\u0026thinsp;S58), that all the SAMs readily formed dense monolayers on the Au\u003csup\u003eTS\u003c/sup\u003e electrode. The I 3\u003cem\u003ed\u003c/em\u003e spectra were ascribed to the terminal I atoms substitution. Based on UPS spectra, we could see that the energy offset (\u003cem\u003e\u0026delta;E\u003c/em\u003e\u003csub\u003e\u003cem\u003eME\u003c/em\u003e\u003c/sub\u003e) between all the investigated SAMs and the bottom electrodes ranged from ~\u0026thinsp;2.1 eV to ~\u0026thinsp;2.4 eV and changed insignificantly, identifying that the SAMs possessed the very similar coupling strength between the SAMs and the Au\u003csup\u003eTS\u003c/sup\u003e electrode (Fig. S59\u0026thinsp;~\u0026thinsp;62, Table \u003cspan class=\"InternalRef\"\u003eS1\u003c/span\u003e\u0026thinsp;~\u0026thinsp;S4).\u003c/p\u003e\n\u003cp\u003eTo analyze how substitutions by I and O atoms affected the rate of electron tunneling across molecular junctions, we measured electrical characteristic curves of the SAMs with varied molecular lengths and averaged log\u003csub\u003e10\u003c/sub\u003e|\u003cem\u003eJ\u003c/em\u003e|\u0026minus;\u003cem\u003eV\u003c/em\u003e plots are shown in Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea and S63 (see Supporting Information Section S4 for details) (Here, \u003cem\u003eJ\u003c/em\u003e and \u003cem\u003eV\u003c/em\u003e were the current density and the applied voltage). Figure S64 containes corresponding histograms of log\u003csub\u003e10\u003c/sub\u003e|\u003cem\u003eJ\u003c/em\u003e| at -0.5V. We made three important observations (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eb): 1) the current density of the SAMs declined with longer molecular length, of which dropped by ~\u0026thinsp;4 and ~\u0026thinsp;2 orders of magnitude for the SAMs of C\u003csub\u003en\u003c/sub\u003e-SH and I-Cn-SH, respectively, when varying n from 5 to 14; 2) the current density of I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003em\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH only attenuated\u0026thinsp;~\u0026thinsp;1 order of magnitude for increasing m from 1 to 4; 3) the value of tunnelling decay coefficient (\u003cem\u003e\u0026beta;\u003c/em\u003e) for molecular junctions of C\u003csub\u003en\u003c/sub\u003e-SH (n\u0026thinsp;=\u0026thinsp;5, 8, 10, 11) was 0.85 similar to previous works \u003csup\u003e30\u003c/sup\u003e, and that of I-C\u003csub\u003en\u003c/sub\u003e-SH(n\u0026thinsp;=\u0026thinsp;5, 8, 10, 11) and (C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003em\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH (m\u0026thinsp;=\u0026thinsp;2, 3, 4) were 0.36 and 0.25, respectively, according to the Simmons equations (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eb). In addition, the conductivity (\u003cem\u003e\u0026sigma;\u003c/em\u003e) (at +\u0026thinsp;0.1V) of I-C\u003csub\u003e11\u003c/sub\u003e-SH in this work was ~\u0026thinsp;2 orders of magnitude larger than that of C\u003csub\u003e11\u003c/sub\u003e-SH, while Nijhuis reported enhancement of 3 orders of magnitude\u003csup\u003e31\u003c/sup\u003e and Whitesides showed that halogen atoms substitution modestly affect the current density\u003csup\u003e32\u003c/sup\u003e. The value of \u003cem\u003e\u0026beta;\u003c/em\u003e for molecular junctions with I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003em\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH (m\u0026thinsp;=\u0026thinsp;1, 2, 3, 4) was 0.18 and indistinguishable from that of conjugated molecular wires,\u003csup\u003e33\u003c/sup\u003e indicating that the SAMs we prepared were densely packed with few defects. What\u0026rsquo;s more, the current density at -0.5V of I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e4\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH was ~\u0026thinsp;4 orders magnitude higher than that of length-matched C\u003csub\u003e14\u003c/sub\u003e-SH (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea and S63), indicating the tunneling barrier was largely reduced by I atoms and O atoms substitutions.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\u0026nbsp;\u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eParameters used to calculate PF for molecular junctions with C\u003csub\u003en\u003c/sub\u003e-SH, I-C\u003csub\u003en\u003c/sub\u003e-SH, (C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003em\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH, I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003em\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e- SH.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"7\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMolecule\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003el\u003c/em\u003e (\u0026Aring;) \u003csup\u003e\u003cem\u003ea\u003c/em\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003el\u003cem\u003eJ\u003c/em\u003e(+\u0026thinsp;0.1V)l\u003c/p\u003e\n \u003cp\u003e(A cm\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e) \u003csup\u003e\u003cem\u003eb\u003c/em\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003e\u0026epsilon;\u003c/em\u003e\u003c/p\u003e\n \u003cp\u003e(GVm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) \u003csup\u003e\u003cem\u003ec\u003c/em\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\sigma\\:\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e\n \u003cp\u003e(\u0026micro;S cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) \u003csup\u003e\u003cem\u003ed\u003c/em\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003e\u003cem\u003eS\u003c/em\u003e\u003c/p\u003e\n \u003cp\u003e(\u0026micro;V K\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e) \u003csup\u003e\u003cem\u003ee\u003c/em\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ePF\u003c/p\u003e\n \u003cp\u003e(10\u003csup\u003e\u0026minus;\u0026thinsp;10\u003c/sup\u003e \u0026micro;W m\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e K\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e) \u003csup\u003e\u003cem\u003ef\u003c/em\u003e\u003c/sup\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC\u003csub\u003e5\u003c/sub\u003e-SH\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.78\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.25\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.173\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.144\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6.6\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6.27\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC\u003csub\u003e8\u003c/sub\u003e-SH\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.110\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.017\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.39\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC\u003csub\u003e11\u003c/sub\u003e-SH\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e12.38\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9.33\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.081\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.115\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.5\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.26\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eC\u003csub\u003e14\u003c/sub\u003e-SH\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e15.66\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.06\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.064\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6.343\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.97\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eI-C\u003csub\u003e5\u003c/sub\u003e-SH\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.23\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.66\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.138\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.478\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e55.75\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eI-C\u003csub\u003e8\u003c/sub\u003e-SH\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10.68\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.11\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.094\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.120\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10.17\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eI-C\u003csub\u003e11\u003c/sub\u003e-SH\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e13.83\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.072\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.042\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.41\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eI-C\u003csub\u003e14\u003c/sub\u003e-SH\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e17.20\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e8.91\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.058\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.015\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.12\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e2\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e8.51\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.118\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.130\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.37\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e3\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e11.63\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.086\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.058\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.02\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e4\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e14.65\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.068\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.029\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.7\u0026thinsp;\u0026plusmn;\u0026thinsp;0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.40\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eI-C\u003csub\u003e2\u003c/sub\u003eO-C\u003csub\u003e2\u003c/sub\u003e-SH\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.08\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e24.00\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.141\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e17.021\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10.8\u0026thinsp;\u0026plusmn;\u0026thinsp;0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.00\u0026times;10\u003csup\u003e3\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eI-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e2\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10.21\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e12.88\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.098\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e13.143\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e11.2\u0026thinsp;\u0026plusmn;\u0026thinsp;0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.64\u0026times;10\u003csup\u003e3\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eI-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e3\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e13.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.075\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.827\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e11.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.18\u0026times;10\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eI-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e4\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e16.37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.061\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.423\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e11.1\u0026thinsp;\u0026plusmn;\u0026thinsp;0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4.22\u0026times;10\u003csup\u003e2\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003e\u003csup\u003e\u0026nbsp;\u003cem\u003ea\u003c/em\u003e\u0026nbsp;\u003c/sup\u003e \u003cem\u003el\u003c/em\u003e represents the molecular length determined by ChemDraw software considering the tilt angle (30\u0026deg;).\u003c/p\u003e\n\u003cp\u003e\u003csup\u003e\u0026nbsp;\u003cem\u003eb\u003c/em\u003e\u0026nbsp;\u003c/sup\u003e Determined from \u003cem\u003eJ\u003c/em\u003e-\u003cem\u003eV\u003c/em\u003e curves in Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ea and S63.\u003c/p\u003e\n\u003cp\u003e\u003csup\u003e\u0026nbsp;\u003cem\u003ec\u003c/em\u003e\u0026nbsp;\u003c/sup\u003e \u003cem\u003e\u0026epsilon;\u003c/em\u003e is the magnitude of electric field intensity and is obtained from the applied voltage across the junctions (+\u0026thinsp;0.1 V) devided by \u003cem\u003el\u003c/em\u003e.\u003c/p\u003e\n\u003cp\u003e\u003csup\u003e\u0026nbsp;\u003cem\u003ed\u003c/em\u003e\u0026nbsp;\u003c/sup\u003e \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\sigma\\:\\)\u003c/span\u003e\u003c/span\u003e is the conductivity of the SAMs and is obtained as \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\sigma\\:\\)\u003c/span\u003e\u003c/span\u003e = \u003cem\u003eJ\u003c/em\u003e/\u003cem\u003e\u0026epsilon;\u003c/em\u003e.\u003c/p\u003e\n\u003cp\u003e\u003csup\u003e\u0026nbsp;\u003cem\u003ee\u003c/em\u003e\u0026nbsp;\u003c/sup\u003e The significant digit of \u003cem\u003eS\u003c/em\u003e is 0.1 \u0026micro;V/K based on the accuracy of the output voltage and the accuracy of the input temperature and was detailed discussed in our previous work.\u003csup\u003e13\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003e\u003csup\u003e\u0026nbsp;\u003cem\u003ef\u003c/em\u003e\u0026nbsp;\u003c/sup\u003e It is difficult to directly estimate the error bar of PF, since the values of PF are calculated from \u003cem\u003eS\u003c/em\u003e and \u003cem\u003e\u0026sigma;\u003c/em\u003e. Therefore, we utilized the average of \u003cem\u003eS\u003c/em\u003e and \u003cem\u003e\u0026sigma;\u003c/em\u003e to obtain PF of the SAMs, and we have noticed that other groups also only reported the error of \u003cem\u003eS\u003c/em\u003e and \u003cem\u003e\u0026sigma;\u003c/em\u003e but not PF.\u003csup\u003e7,8,10,34\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003eTo characterize \u003cem\u003eS\u003c/em\u003e of molecular junctions, we recorded potential difference (\u003cem\u003e\u0026Delta;V\u003c/em\u003e) in response of temperature difference (\u003cem\u003e\u0026Delta;T\u003c/em\u003e\u0026thinsp;=\u0026thinsp;2.0 K, 3.5 K, 5.0 K) applied on the SAMs with heating the bottom Au\u003csup\u003eTS\u003c/sup\u003e electrode and cooling the top EGaIn electrode. The corresponding setup and analysis protocol of thermoelectric measurements was reported by our previous study as shown in Fig. S65 (see Supporting Information Section S5 for details).\u003csup\u003e13\u003c/sup\u003e Here, we give a brief description. For each SAM at applied \u003cem\u003e\u0026Delta;T\u003c/em\u003e, we measured at least 20 junctions to generate statistical significant data to determine average of \u003cem\u003e\u0026Delta;V\u003c/em\u003e (\u0026lt;\u003cem\u003e\u0026Delta;V\u003c/em\u003e\u0026gt;) and related standard-deviation by Gaussians fitting (Fig. S66\u0026thinsp;~\u0026thinsp;70). Then, the values of \u003cem\u003eS\u003c/em\u003e for molecular junctions can be obtained by plotting\u0026thinsp;\u0026lt;\u0026thinsp;\u003cem\u003e\u0026Delta;V\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;as a function of \u003cem\u003e\u0026Delta;T\u003c/em\u003e (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ec and S71). After detailed analysis of dependence between measured\u0026thinsp;\u0026lt;\u0026thinsp;\u003cem\u003e\u0026Delta;V\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;and \u003cem\u003eS\u003c/em\u003e (reported in our previous work), we acquired the values of \u003cem\u003eS\u003c/em\u003e for the SAMs as listed in Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e. We observed: 1) the positive sign of \u003cem\u003eS\u003c/em\u003e for the investigated molecules indicated HOMO dominated charge transport properties in all cases; 2) engineering molecules by terminal I atom substitution and replacing backbone -CH\u003csub\u003e2\u003c/sub\u003e- unite with O atom could result in the enhanced values of \u003cem\u003eS\u003c/em\u003e comparing with C\u003csub\u003en\u003c/sub\u003e-SH; 3) \u003cem\u003eS\u003c/em\u003e for the SAMs of C\u003csub\u003en\u003c/sub\u003e-SH, I-C\u003csub\u003en\u003c/sub\u003e-SH and (C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003em\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH declined with increased molecular length; 4) the values of \u003cem\u003eS\u003c/em\u003e for the SAMs of I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003em\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH, ~\u0026thinsp;11 \u0026micro;V/K, were nearly independent on molecular length, and that of I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e4\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH was ~\u0026thinsp;4 times higher than C\u003csub\u003e14\u003c/sub\u003e-SH (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ed). Therefore, combining these substitutions could enhance the Seebeck coefficient of the SAMs, which is a crucial step toward enhancing the thermoelectric performance of molecular junctions.\u003c/p\u003e\n\u003cp\u003eTo evaluate the enhancement of the thermoelectric effect, we calculated the values of PF of each SAM (Fig. \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003ee and Table \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e) and the detailed processes were reported in Supporting Information Section S5. It is interesting that values of log\u003csub\u003e10\u003c/sub\u003ePF linearly attenuated with the molecular length, which has not been reported before. We think the reasons could be 1) terminal I atom substitution and replacing backbone methylene units (-CH\u003csub\u003e2\u003c/sub\u003e-) by O atom improved the current density ranging from 2 to 4 orders of magnitude and the measured log\u003csub\u003e10\u003c/sub\u003e|\u003cem\u003eJ\u003c/em\u003e| followed a good linear correlation with molecular length, 2) the increase of \u003cem\u003eS\u003c/em\u003e by the atomically tuned chemical structures was less than 5 times and the sharply promoted PF was mainly originated for the change of \u003cem\u003eG\u003c/em\u003e, resulting in the calculated PF being basically linearly related to the molecular length. The values of PF enhanced by 1\u0026ndash;2 orders of magnitude through I atoms substitution, so does backbone O atom substitution. When m\u0026thinsp;=\u0026thinsp;1 for I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003em\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH, its PF improved by ~\u0026thinsp;3 orders of magnitude compared with C\u003csub\u003e5\u003c/sub\u003e-SH. The longer the molecular length, the greater of degree of improvement. The PF of I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e4\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH was ~\u0026thinsp;8.5\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{\u0026times;}\\)\u003c/span\u003e\u003c/span\u003e10\u003csup\u003e5\u003c/sup\u003e times higher that of C\u003csub\u003e14\u003c/sub\u003e-SH, demonstrating our molecular design could dramatically boosted PF of the SAMs. As reported by Agra\u0026iuml;t\u003csup\u003e19\u003c/sup\u003e and Lambert\u003csup\u003e35\u003c/sup\u003e, the occurrence of resonant states in \u003cem\u003e\u0026tau;\u003c/em\u003e(\u003cem\u003eE\u003c/em\u003e) near \u003cem\u003eE\u003c/em\u003e\u003csub\u003eF\u003c/sub\u003e could bring enhancement both for \u003cem\u003eS\u003c/em\u003e and \u003cem\u003eG\u003c/em\u003e. Therefore, we proposed that the molecular engineering in this work not only increased SAMs/EGaIn electrode coupling, reducing barrier of electron tunneling, but also modified mechanism of charge transport from coherent tunneling to superexchange tunneling via lone-pair electrons on O atoms. Under synergistic effect of these substitutions, the molecular energy levels of I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003em\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH resonated with \u003cem\u003eE\u003c/em\u003e\u003csub\u003eF\u003c/sub\u003e of electrodes, which resulted in the simultaneously enhanced \u003cem\u003eS\u003c/em\u003e and \u003cem\u003eG\u003c/em\u003e and approximately 6 orders of magnitude improvement of PF for I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e4\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH compared with C\u003csub\u003e14\u003c/sub\u003e-SH.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTheoretical estimation of\u003c/strong\u003e \u003cstrong\u003eG\u003c/strong\u003e, \u003cstrong\u003eS\u003c/strong\u003e \u003cstrong\u003eand PF of the molecular junctions.\u003c/strong\u003e To gain a deeper insight into the above mentioned results that atomically precise engineering of the organic molecules could improve \u003cem\u003eS\u003c/em\u003e and \u003cem\u003eG\u003c/em\u003e, we carried out theoretical transport calculations for the molecular junctions with C\u003csub\u003en\u003c/sub\u003e-SH and I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003em\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH as shown in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e. The electronic structure calculations were performed at the DFT level using SIESTA\u003csup\u003e36\u003c/sup\u003e. The transmission spectra of molecular junctions were calculated using the non-equilibrium Green\u0026rsquo;s function (NEGF) method implemented in TRANSIESTA\u003csup\u003e37,38\u003c/sup\u003e. Afterwards, the linear response scheme was adopted to obtain the thermoelectric coefficients.\u003csup\u003e39\u0026ndash;42\u003c/sup\u003e The \u003cem\u003eG\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e and PF can be written as follows:\u003c/p\u003e\n\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e$$\\:\\:\\:\\:\\:\\:\\:\\:G(\\mu\\:,\\:T)={\\left.\\frac{I}{{\\Delta\\:}V}\\right|}_{\\varDelta\\:T=0}={e}^{2}{L}_{0}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e$$\\:S(\\mu\\:,\\:T)={\\left.-\\frac{{\\Delta\\:}V}{{\\Delta\\:}T}\\right|}_{I=0}=-\\frac{1}{eT}\\frac{{L}_{1}}{{L}_{0}}$$\u003c/div\u003e\n \u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e$$\\:\\text{P}\\text{F}=G{S}^{2}$$\u003c/div\u003e\n \u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eHere the coefficient \u003cem\u003eL\u003c/em\u003e\u003csub\u003e\u003cem\u003en\u003c/em\u003e\u003c/sub\u003e is dependent on the transmission coefficient.\u003c/p\u003e\n\u003cdiv id=\"Equ4\" class=\"Equation\"\u003e\n \u003cdiv class=\"mathdisplay\" id=\"FileID_Equ4\" name=\"EquationSource\"\u003e$$\\:{L}_{n}(\\mu\\:,\\:T)=\\frac{1}{h}{\\int\\:}_{-\\infty\\:}^{\\infty\\:}{\\left(E-\\mu\\:\\right)}^{n}T\\left(E\\right)(-\\frac{\\partial\\:f(E,\\mu\\:,T)}{\\partial\\:E})dE$$\u003c/div\u003e\n \u003cdiv class=\"EquationNumber\"\u003e4\u003c/div\u003e\n\u003c/div\u003e\n\u003cp\u003eThe optimized structure of molecular junctions of C\u003csub\u003en\u003c/sub\u003e-SH and I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003em\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH are shown in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ea and S72\u0026thinsp;~\u0026thinsp;S73, where we utilized Au as the top electrode and use a constant self-energy to avoid the complication in modeling the EGaIn electrode, which has been done previously\u003csup\u003e43\u0026ndash;45\u003c/sup\u003e. The molecule together with one extra layer of Au from each side were fully relaxed until the forces acting on each atoms were less than 0.02 eV/\u0026Aring;.\u003c/p\u003e\n\u003cp\u003eThe transmission coefficient of C\u003csub\u003en\u003c/sub\u003e-SH gets lower as the molecular length increases as shown in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003eb and S74, which is the consequence of broader tunneling barriers for longer molecule. New resonances in the junctions formed by I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003em\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH are found around \u003cem\u003eE\u003c/em\u003e = -1.83 eV (as indicated by the black dashed line in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ec). Since they (\u003cem\u003eE\u003c/em\u003e = -1.83 eV) are further away from the calculated Fermi energy (\u003cem\u003eE\u0026thinsp;=\u003c/em\u003e\u0026thinsp;0 eV), their contribution to transport properties is negligible. However, in previous experimental studies signature of enhanced conductance due to these states were reported\u003csup\u003e44\u003c/sup\u003e. Several reasons may results in such discrepancy between theoretical and experimental results. One is that the standard DFT calculation is not accurate enough, especially in determining the Fermi level. The second could be that, the coupling between different molecules may lead to broadening these resonant states. To understand qualitatively the experimental results, we have chosen to take the Fermi energy as a tuning parameter. We have calculated the thermoelectric transport coefficients (\u003cem\u003eG\u003c/em\u003e, \u003cem\u003eS\u003c/em\u003e and PF) using different Fermi energy values for C\u003csub\u003en\u003c/sub\u003e-SH and I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003em\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH, which are shown in Fig. S75\u0026thinsp;~\u0026thinsp;S77. We find that only when the Fermi level is located near these resonant states, could the theoretical results be consistent with experimental ones (Fig. S78\u0026thinsp;~\u0026thinsp;S79).\u003c/p\u003e\n\u003cp\u003eWe have shown theoretical results for \u003cem\u003eE\u003c/em\u003e\u003csub\u003eF\u003c/sub\u003e = -1.83 eV in Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e. In this case, the improvement of both \u003cem\u003eG\u003c/em\u003e and \u003cem\u003eS\u003c/em\u003e for I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003em\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH observed in the experiments can be reproduced from the DFT calculations (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ed, e). We have the following observations (Fig. \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003ef): 1) the values of PF for the SAMs of C\u003csub\u003en\u003c/sub\u003e-SH gradually declined with the increased molecular length; 2) the PF of I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003em\u003c/sub\u003e-SH were always higher than those of C\u003csub\u003en\u003c/sub\u003e-SH for the equivalent molecular lengths; 3) the PF of I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e4\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH was approximately 4 orders of magnitude larger than C\u003csub\u003e14\u003c/sub\u003e-SH. Therefore, the theoretical results offered a qualitative understanding of the experimental measurements, indicating that the molecular engineering method in this work could significantly increase the PF of molecular junctions, which is promising for further development of organic thermoelectric materials at nanoscale. In addition, the measured \u003cem\u003eS\u003c/em\u003e of the SAMs of I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003em\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH derivatives were much lower than the theoretically predicted values, highlighting that futher efforts should be devoted on the finely-tuning the electronic structures of molecular junctions to engineering the quantum transport properties for the high-performance thermoelectronic devices.\u003c/p\u003e\n\u003cdiv class=\"BlockQuote\"\u003e\n \u003cp\u003eIn conclusion, we focused on how the heteroatom substitution, including the terminal I atom substitution and replacing the backbone -CH\u003csub\u003e2\u003c/sub\u003e- by O atoms, affected the charge transport across molecular junctions, and confirmed that both \u003cem\u003eG\u003c/em\u003e and \u003cem\u003eS\u003c/em\u003e could be improved in the SAMs of I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003em\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH (m\u0026thinsp;=\u0026thinsp;1, 2, 3, 4), compared to the length-matched C\u003csub\u003en\u003c/sub\u003e-SH (n\u0026thinsp;=\u0026thinsp;5, 8, 11, 14). According to the electrical tunneling results, the values of \u003cem\u003e\u0026beta;\u003c/em\u003e for the SAMs of C\u003csub\u003en\u003c/sub\u003e-SH and I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003em\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH were 0.85 and 0.18, respectively, indicating the sharply declined tunneling barrier, and the value of \u003cem\u003e\u0026sigma;\u003c/em\u003e (at +\u0026thinsp;0.1V) for I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e4\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH was more than 4 orders of magnitude larger than that of C\u003csub\u003e14\u003c/sub\u003e-SH. In addition, the values of \u003cem\u003eS\u003c/em\u003e for the SAMs of C\u003csub\u003en\u003c/sub\u003e-SH, I-C\u003csub\u003en\u003c/sub\u003e-SH and (C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003em\u003c/sub\u003e-SH declined with increased molecular length, while that for the SAMs of I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003em\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH, ~\u0026thinsp;11 \u0026micro;V/K, were nearly independent on molecular length. The \u003cem\u003eS\u003c/em\u003e of I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e4\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH was ~\u0026thinsp;4 times higher than that of C\u003csub\u003e14\u003c/sub\u003e-SH. Therefore, the PF of I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e4\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH was dramatically enhanced by a factor of 8.5\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\text{\u0026times;}\\)\u003c/span\u003e\u003c/span\u003e10\u003csup\u003e5\u003c/sup\u003e compering with C\u003csub\u003e14\u003c/sub\u003e-SH. Based on the DFT calculations, the underline mechanism was that the new resonances were introduced into the SAMs after heteroatom substitution near the Fermi energy. This work highlighted the importance of molecular engineering for nano thermoelectric devices with high-efficiency conversion of the wasted heat to the useful electricity.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"Methods","content":"\u003cp\u003eAll the experimental and theoretical data can be found in the supplemental information, including\u0026nbsp;the synthetic processes of the compounds,\u0026nbsp;the preparation of the Au\u003csup\u003eTS\u003c/sup\u003e electrode and the SAMs, the characterization of the SAMs, the electrical and thermoelectric measurement as well as the DFT calculation.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe data that support the findings of this study are available within the article and its Supplementary Information files. All data underlying the findings of this work are available from the corresponding author upon request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCode availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe code used for the analyses is available from the corresponding authors on reasonable request.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting interests\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eY. L. initiated the project and designed the experiments. W. P. synthesized the molecules. Y. X. prepared the bottom electrode. W. P. carried out electrical and thermoelectric measurements. N. C. performed surface characterization of SAMs, including XPS and UPS. L. M. and J. L. conducted DFT calculations. W. P., N. C., Y. L., L. M. and J. L. analyzed experimental data and contributed mainly to the writing of the manuscript. All authors discussed the results, data analysis, and contributed to the writing of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNational Natural Science Foundation of China (22273045 and 62201494), Tsinghua University Independent Scientific Research Plan for Young Investigator, Tsinghua University Initiative Scientific Research Program and \u0026ldquo;Dushi\u0026rdquo; program. We also gratefully acknowledge NCESBJ (National Center of Electron Spectroscopy in Beijing) where the SAMs characterization was conducted.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAdditional information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eSupplementary information\u003c/strong\u003e The online version contains supplementary material available at https://doi.org/xx.xxxx/xxxxxx-xxx-xxxxx-x.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eRinc\u0026oacute;n-Garc\u0026iacute;a, L., Evangeli, C., Rubio-Bollingera, G. \u0026amp; Agra\u0026iuml;t, N. Thermopower measurements in molecular junctions. \u003cem\u003eChem. Soc. Rev.\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e45\u003c/em\u003e\u003c/strong\u003e, 4285 (\u003cstrong\u003e2016\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eWang, K., Meyhofer, E. \u0026amp; Reddy, P. Thermal and thermoelectric properties of molecular junctions. \u003cem\u003eAdv. Funct. Mater.\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e30\u003c/em\u003e\u003c/strong\u003e, 1904534 (\u003cstrong\u003e2019\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eYu‐Jia, Z.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Nanoscale Organic Thermoelectric Materials: Measurement, Theoretical Models, and Optimization Strategies. \u003cem\u003eAdv. Funct. Mater.\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e30\u003c/em\u003e\u003c/strong\u003e, 1903873 (\u003cstrong\u003e2019\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eSohyun, P., Hungu, K. \u0026amp; Jae, Y. H. Structure\u0026ndash;thermopower relationships in molecular thermoelectrics. \u003cem\u003eJ. Mater. Chem. A\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e7\u003c/em\u003e\u003c/strong\u003e, 14419 (\u003cstrong\u003e2019\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eCui, L.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Peltier cooling in molecular junctions. \u003cem\u003eNat. Nanotechnol.\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e13\u003c/em\u003e\u003c/strong\u003e, 122 (\u003cstrong\u003e2018\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eCui, L.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Thermal conductance of single-molecule junctions. \u003cem\u003eNature\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e572\u003c/em\u003e\u003c/strong\u003e, 628 (\u003cstrong\u003e2019\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eGehring, P.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Complete mapping of the thermoelectric properties of a single molecule. \u003cem\u003eNat. Nanotechnol.\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e16\u003c/em\u003e\u003c/strong\u003e, 426 (\u003cstrong\u003e2021\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eXu, H.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Electrical Conductance and Thermopower of \u003cem\u003e\u0026beta;\u003c/em\u003e‑Substituted Porphyrin Molecular Junctions-Synthesis and Transport. \u003cem\u003eJ. Am. Chem. Soc.\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e145\u003c/em\u003e\u003c/strong\u003e, 23541 (\u003cstrong\u003e2023\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eLi, M.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Electrically gated molecular thermal switch. \u003cem\u003eScience\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e382\u003c/em\u003e\u003c/strong\u003e, 585 (\u003cstrong\u003e2023\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003ePark, S., Kang, S. \u0026amp; Yoon, H. J. Power factor of one molecule thick films and length dependence. \u003cem\u003eACS Cent. Sci.\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e5\u003c/em\u003e\u003c/strong\u003e, 1975 (\u003cstrong\u003e2019\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eSowa, J. K., Mo, J. A. \u0026amp; Gauger, E. M. Marcus theory of thermoelectricity in molecular junctions.\u003cem\u003e\u0026nbsp;J. Phys. Chem. C .\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e123\u003c/em\u003e\u003c/strong\u003e, 4103 (\u003cstrong\u003e2019\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eChen, R., Lee, J., Lee, W. \u0026amp; Li, D. Thermoelectrics of Nanowires. \u003cem\u003eChem. Rev.\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e119\u003c/em\u003e\u003c/strong\u003e, 9260 (\u003cstrong\u003e2019\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003ePeng, W., Cao, Z., Chen, N., Xie, Y. \u0026amp; Li, Y. Dependence of thermoelectric effects in molecular junctions on the topography of the bottom electrodes. \u003cem\u003eJ. Mater. Chem. A\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e10\u003c/em\u003e\u003c/strong\u003e, 23304 (\u003cstrong\u003e2022\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eGemma, A. \u0026amp; Gotsmann, B. A roadmap for molecular thermoelectricity. \u003cem\u003eNat. Nanotechnol.\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e16\u003c/em\u003e\u003c/strong\u003e, 1299 (\u003cstrong\u003e2021\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eDatta, S. Electronic transport in mesoscopic systems, Cambridge University, Cambridge, UK. \u003cem\u003eElectronic transport in mesoscopic systems\u003c/em\u003e\u003cstrong\u003eCambridge University\u003c/strong\u003e (\u003cstrong\u003e1995\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eMohaddespour, A., Abolghasemi, H., Mostaedi, M. T. \u0026amp; Habibzadeh, S. A new model for estimation of the thermal conductivity of polymer/clay nanocomposites. \u003cem\u003eJ. Appl. Polym.\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e118\u003c/em\u003e\u003c/strong\u003e, 1042 (\u003cstrong\u003e2010\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eRuan, K. \u0026amp; Gu, J. Ordered alignment of liquid crystalline graphene fluoride for significantly enhancing thermal conductivities of liquid crystalline polyimide composite films. \u003cem\u003eMacromolecules\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e55\u003c/em\u003e\u003c/strong\u003e, 4134 (\u003cstrong\u003e2022\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eLiua, Z., Wei, H., Tangb, B., Xuc, S. \u0026amp; Shufen, Z. Novel light\u0026ndash;driven CF/PEG/SiO\u003csub\u003e2\u003c/sub\u003e composite phase change materials with high thermal conductivity. \u003cem\u003eSol. Energy Mater.\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e174\u003c/em\u003e\u003c/strong\u003e, 538 (\u003cstrong\u003e2018\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eHurtado-Gallego, J.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Thermoelectric enhancement in single organic radical molecules. \u003cem\u003eNano Lett.\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e22\u003c/em\u003e\u003c/strong\u003e, 948 (\u003cstrong\u003e2022\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eIsmael, A. K.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Exploring seebeck-coefficient fluctuations in endohedral-fullerene, single-molecule junctions. \u003cem\u003eNanoscale Horiz.\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e7\u003c/em\u003e\u003c/strong\u003e, 616 (\u003cstrong\u003e2022\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eNaher, M.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Molecular structure-(thermo)electric property relationships in single-molecule junctions and comparisons with single- and multiple-parameter models. \u003cem\u003eJ. Am. Chem. Soc.\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e143\u003c/em\u003e\u003c/strong\u003e, 3817 (\u003cstrong\u003e2021\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eWang, X.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Scale-up of room-temperature constructive quantum interference from single molecules to self-assembled molecular-electronic films. \u003cem\u003eJ. Am. Chem. Soc. \u003cstrong\u003e142\u003c/strong\u003e\u003c/em\u003e, 8555 (\u003cstrong\u003e2020\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eIsmael, A.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Tuning the thermoelectrical properties of anthracene-based self-assembled monolayers. \u003cem\u003eChem. Sci.\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e11\u003c/em\u003e\u003c/strong\u003e, 6836 (\u003cstrong\u003e2020\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eJang, J., Jo, J. W., Ohto, T. \u0026amp; Yoon, H. J. Seebeck effect in molecular wires facilitating long-range transport. \u003cem\u003eJ. Am. Chem. Soc.\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e146\u003c/em\u003e\u003c/strong\u003e, 4922 (\u003cstrong\u003e2024\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eMiao, R.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Influence of quantum interference on the thermoelectric properties of molecular junctions. \u003cem\u003eNano Lett.\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e18\u003c/em\u003e\u003c/strong\u003e, 5666 (\u003cstrong\u003e2018\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eBaghbanzadeh, M.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Anomalously Rapid Tunneling: Charge Transport across Self-Assembled Monolayers of Oligo(ethylene glycol). \u003cem\u003eJ. Am. Chem. Soc.\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e139\u003c/em\u003e\u003c/strong\u003e, 7624 (\u003cstrong\u003e2017\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eCho, N.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Superexchange Coupling-Induced Enhancements of Thermoelectric Performance in Saturated Molecules. \u003cem\u003eNano Lett\u003c/em\u003e\u003cstrong\u003e21\u003c/strong\u003e, 360 (\u003cstrong\u003e2021\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eChen, X.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e A single atom change turns insulating saturated wires into molecular conductors. \u003cem\u003eNat. Commun.\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e12\u003c/em\u003e\u003c/strong\u003e, 3432 (\u003cstrong\u003e2021\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eLin, J.-L.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Molecular diodes with tunable threshold voltage based on \u0026pi;‐extended tetrathiafulvalene. \u003cem\u003eAdv. Mater. Interfaces\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e9\u003c/em\u003e\u003c/strong\u003e, 2201238 (\u003cstrong\u003e2022\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eLi, Y., Jiang, L., Zhang, B. \u0026amp; Nijhuis, C. A. Dependency of the tunneling decay coefficient in molecular tunneling junctions on the topography of the bottom electrodes. \u003cem\u003eAngew. Chem. Int. Edit.\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e53\u003c/em\u003e\u003c/strong\u003e, 3377 (\u003cstrong\u003e2014\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eWang, D.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Tuning the Tunneling Rate and Dielectric Response of SAM-Based Junctions via a Single Polarizable Atom. \u003cem\u003eAdv. Mater.\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e27\u003c/em\u003e\u003c/strong\u003e, 6689 (\u003cstrong\u003e2015\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eBaghbanzadeh, M., Pieters, P. F., Li, Y., Collison, D. \u0026amp; Whitesides, G. M. The rate of charge tunneling in EGaIn junctions is not sensitive to halogen substituents at the self-assembled monolayer//Ga\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e interface. \u003cem\u003eACS Nano\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e12\u003c/em\u003e\u003c/strong\u003e, 10221 (\u003cstrong\u003e2018\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eXie, Z., Bâldea, I., Smith, C. E., Wu, Y. \u0026amp; Frisbie, C. D. Experimental and theoretical analysis of nanotransport in oligophenylene dithiol junctions as a function of molecular length and contact work function. \u003cem\u003eACS Nano\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e8\u003c/em\u003e\u003c/strong\u003e, 8022 (\u003cstrong\u003e2015\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eRinc\u0026oacute;n-Garc\u0026iacute;a, L.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Molecular design and control of fullerene-based bi-thermoelectric materials. \u003cem\u003eNat. Mater.\u003c/em\u003e\u003cstrong\u003e15\u003c/strong\u003e, 289 (\u003cstrong\u003e2016\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eWang, K.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Charge transfer complexation boosts molecular conductance through Fermi level pinning. \u003cem\u003eChem. Sci.\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e10\u003c/em\u003e\u003c/strong\u003e, 2396 (\u003cstrong\u003e2019\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eSoler, J. M.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e The SIESTA method for ab initio order-N materials simulation. \u003cem\u003eJ. Phys.: Condens. Matter\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e14\u003c/em\u003e\u003c/strong\u003e, 2745 (\u003cstrong\u003e2002\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eBrandbyg, M., Mozos, J.-L., Ordej\u0026oacute;n, P., Taylor, J. \u0026amp; Stokbro, K. Density-functional method for nonequilibrium electron transport. \u003cem\u003ePhys. Rev. B\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e65\u003c/em\u003e\u003c/strong\u003e, 165401 (\u003cstrong\u003e2002\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003ePapior, N., Lorente, N., Frederiksen, T., Garc\u0026iacute;a, A. \u0026amp; Brandbyge, M. Improvements on non-equilibrium and transport Green function techniques: The next-generation TRANSIESTA. \u003cem\u003eComput. Phys. Commun.\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e212\u003c/em\u003e\u003c/strong\u003e, 8 (\u003cstrong\u003e2017\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eBergfield, J. P. \u0026amp; Stafford, C. A. Thermoelectric signatures of coherent transport in single-molecule heterojunctions. \u003cem\u003eNano Lett.\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e9\u003c/em\u003e\u003c/strong\u003e, 3072 (\u003cstrong\u003e2009\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eRen, J., Zhu, J.-X., Gubernatis, J. E., Wang, C. \u0026amp; Li, B. Thermoelectric transport with electron-phonon coupling and electron-electron interaction in molecular junctions. \u003cem\u003ePhys. Rev. B\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e85\u003c/em\u003e\u003c/strong\u003e, 155443 (\u003cstrong\u003e2012\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eBevilacqua, G., Grosso, G., Menichetti, G. \u0026amp; Parravicini, G. P. Thermoelectric efficiency of nanoscale devices in the linear regime. \u003cem\u003ePhys. Rev. B\u003c/em\u003e\u003cstrong\u003e94\u003c/strong\u003e, 245419 (\u003cstrong\u003e2016\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eMa, L., Nian, L.-L. \u0026amp; L\u0026uuml;, J.-T. Design and optimization of a heat engine based on a porphyrin single-molecule junction with graphene electrodes. \u003cem\u003ePhys. Rev. B\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e101\u003c/em\u003e\u003c/strong\u003e, 045410 (\u003cstrong\u003e2020\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eSoni, S.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Understanding the role of parallel pathways via in-situ switching of quantum interference in molecular tunneling junctions. \u003cem\u003eAngew. Chem. Int. Ed.\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e59\u003c/em\u003e\u003c/strong\u003e, 14308 (\u003cstrong\u003e2020\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eHu, Y.\u003cem\u003e\u0026nbsp;et al.\u003c/em\u003e Single dynamic covalent bond tailored responsive molecular junctions. \u003cem\u003eAngew. Chem. Int. Ed. Engl.\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e60\u003c/em\u003e\u003c/strong\u003e, 20872 (\u003cstrong\u003e2021\u003c/strong\u003e).\u003c/li\u003e\n \u003cli\u003eKong, G. D., Byeon, S. E., Jang, J., Kim, J. W. \u0026amp; Yoon, H. J. Electronic mechanism of \u003cem\u003ein situ\u003c/em\u003e inversion of rectification polarity in supramolecular engineered monolayer. \u003cem\u003eJ. Am. Chem. Soc.\u003c/em\u003e\u003cstrong\u003e\u003cem\u003e144\u003c/em\u003e\u003c/strong\u003e, 7966 (\u003cstrong\u003e2022\u003c/strong\u003e).\u003c/li\u003e\n\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":"Thermoelectric effects, Power factor, Self-assembled monolayer, Heteroatom substitution, Tunnelling","lastPublishedDoi":"10.21203/rs.3.rs-4763672/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4763672/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eEngineering power factor (PF) of molecular junctions is one of the most attractive research in the field of thermoelectronics for the applications in thermal management and high-performance thermoelectric energy conversion at the nanoscale. Here, we modified the chemical structure of self-assembled monolayers (SAMs) formed by the widely investigated alkanethiolate (C\u003csub\u003en\u003c/sub\u003e-SH, n = 5, 8, 11, 14) through heteroatom substitutions, including the terminal iodine (I) atom substitution and replacing backbone methylene units (-CH\u003csub\u003e2\u003c/sub\u003e-) with oxygen (O) atoms, to obtain iodo-substituted oligo(ethylene glycol) thiolates (I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003em\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH, m = 1, 2, 3, 4). We carried out the electrical tunneling and thermoelectric measurements based on the eutectic Ga-In technique (EGaIn) and found that the electrical conductance (\u003cem\u003eG\u003c/em\u003e) and Seebeck coefficient (\u003cem\u003eS\u003c/em\u003e) of the SAMs with I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003em\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH can be enhanced simultaneously compared to the length-matched SAMs of C\u003csub\u003en\u003c/sub\u003e-SH (n = 3m + 2), resulting in the PF of I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003e4\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH being over 5 orders of magnitude higher than that of C\u003csub\u003e14\u003c/sub\u003e-SH, which was attributed to the resonant states contributed from the substituted I-(C\u003csub\u003e2\u003c/sub\u003eO)\u003csub\u003em\u003c/sub\u003e-C\u003csub\u003e2\u003c/sub\u003e-SH near the Fermi energy. This study underscored the significance of chemically engineering the organic molecules to dramatically boost PF of molecular junctions for the further applications of high-efficient nanoscale thermoelectric devices.\u003c/p\u003e","manuscriptTitle":"Heteroatom engineering enhancing thermoelectric power factor of molecular junctions","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-07-30 07:40:27","doi":"10.21203/rs.3.rs-4763672/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":"48895b62-4a75-42b6-b408-4991c9c97821","owner":[],"postedDate":"July 30th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":35193609,"name":"Physical sciences/Energy science and technology/Thermoelectric devices and materials"},{"id":35193610,"name":"Physical sciences/Materials science/Nanoscale materials/Molecular self-assembly"}],"tags":[],"updatedAt":"2024-08-19T10:40:17+00:00","versionOfRecord":[],"versionCreatedAt":"2024-07-30 07:40:27","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4763672","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4763672","identity":"rs-4763672","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}