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.