Tailoring of a Visible-Light-Absorbing Biaxial Ferroelectric towards Broadband Self-Driven Photodetection

In term of strong light-polarization coupling, ferroelectric materials with bulk photovoltaic effects (BPVEs) afford a promising avenue for newly-conceptual optoelectronic devices. However, due to severe polarization deterioration caused by leakage current of photoexcited carriers, most of ferroelectrics are merely capable of absorbing 8 ~ 20% of visible-light spectra. BPVE-active ferroelectrics with the narrow bandgap ( E g < 2.0 eV) are still scarce, hindering their practical applications. Here, we present a new 2D lead-iodide hybrid biaxial ferroelectric, [(CH 3 ) 2 CH(CH 2 ) 2 NH 3 ] 2 (CH 3 CH 2 NH 3 ) 2 Pb 3 I 10 ( 1 ), which shows large spontaneous polarization ( P s = 5.2 µC/cm 2 ) and the narrow direct bandgap ( E g = 1.80 eV). To the best of our knowledge, this E g value of 1 is the smallest figure ever observed for the existing molecular ferroelectrics. Particularly, the symmetry breaking of 4/ mmm F mm 2 species results in its biaxial attributes, that is, four equivalent P s directions for 1 . Accordingly, exceptional in-plane BPVEs are exploited along the crystallographic [001] and [010] axes directions inside the crystallographic bc -plane, of which the directions can be facilely switched through external electric poling. At zero bias, the intriguing self-driven photoactivities were created in a wide range of 365–670 nm, including large switching ratio (> 10 5 ), high-density photocurrent (~ 1.5 µA/cm 2 ) and ultrafast transient responding time (~ 2.7 ns). It is the coupling between ferroelectricity and in-plane BPVEs that endows great potentials of 1 toward broadband self-driven photodetection. This innovative study on in-plane ferroelectric BPVEs is unprecedent, which sheds light on new properties for their future optoelectronic device applications.