A‐Site Diamine Cation Anchoring Enables Efficient Charge Transfer and Suppressed Ion Migration in Bi‐Based Hybrid Perovskite Single Crystals

Due to the large distance or weak electronic conjugation between adjacent Bi-I octahedrons, the charge transport in the low-dimensional bismuth-based hybrid perovskites is impeded and thus hinders their future developments. In this work, A-site cation engineering by monoamine BZA (benzylamine) and diamine 3-AMP (3-(aminomethyl)pyridine) has been demonstrated as an efficient strategy to regulate the corresponding activation energy of ionic migration and carrier transport capacity. Given the higher polarity of 3-AMP than BZA, producing a more efficient dielectric screening effect, it gives rise to obtaining the small exciton binding energy (50 meV) and low defect states (3.53×10⁹ cm^-3 ). The reduced distance of adjacent Bi-I octahedrons by the bilateral anchoring of the 3-AMP²⁺ diamine cation enhances both electronic conjugation and charge transport performance. Therefore, the photodetector for (3-AMP)BiI₅ SC shows a 243-fold increase in on/off ratio compared with the (BZA)₃ BiI₆ SC.