Bismuth-Based Zero-Dimensional Perovskite-like Materials: Effect of Benzylammonium on Dielectric Confinement and Photoconductivity

Bismuth-based perovskite-like materials are considered as promising alternatives to lead-based perovskites for optoelectronic applications. However, the major drawbacks of these materials are high exciton binding energy and poor charge-carrier separation efficiency. These issues are attributed to the strong quantum and dielectric confinements associated with these materials. In this work, we have used a simple methodology to reduce the dielectric confinement in hybrid A3Bi2I9 type perovskite-like materials (A is an organic cation) to improve the charge-carrier separation efficiency. For that, the electronically inert methylammonium (MA) was replaced with a polarizable benzylammonium (BA) cation in the well-studied MA3Bi2I9 (MBI) structure. The single-crystal X-ray diffraction (XRD) and ultraviolet–visible (UV–vis) absorption spectroscopy analyses suggested similar quantum confinement in both (BA)3Bi2I9 (BBI) and MBI materials. This enabled us to precisely investigate the role of polarizable benzylammonium cations in the dielectric confinement in BBI. Flash-photolysis time-resolved microwave conductivity studies revealed about 2.5-fold enhancement of φ∑μ (the product of charge-carrier generation quantum yield and the sum of charge-carrier mobilities) for BBI when compared to that of MBI, which is attributed to the low dielectric confinement in the former.