Single- or double A-site cations in A3Bi2I9 bismuth perovskites: What is the suitable choice?
Feray Ünlü, Ashish Kulkarni, Khan Lê, Christoph Bohr, Andrea Bliesener, Seren Dilara Öz, Ajay Kumar Jena, Yoichi Ando, Tsutomu Miyasaka, Thomas Kirchartz, Sanjay Mathur
Abstract
Abstract Investigations on the effect of single or double A-site cation engineering on the photovoltaic performance of bismuth perovskite-inspired materials (A 3 Bi 2 I 9 ) are rare. Herein, we report novel single- and double-cation based bismuth perovskite-inspired materials developed by (1) completely replacing CH 3 NH 3 + (methylammonium, MA + ) in MA 3 Bi 2 I 9 with various organic cations such as CH(NH 2 ) 2 + (formamidinium, FA + ), (CH 3 ) 2 NH 2 + (dimethylammonium, DMA + ), C(NH 2 ) 3 + (guanidinium, GA + ) and inorganic cations such as cesium (Cs + ), rubidium (Rb + ), potassium (K + ), sodium (Na + ) and lithium (Li + ) and (2) partially replacing MA + with Cs + in different stoichiometric ratios. Compared to single-cation based bismuth perovskite devices, the double-cation bismuth perovskite device showed an increment in the device power conversion efficiency (PCE) up to 1.5% crediting to the reduction in the bandgap. This is the first study demonstrating double-cation based bismuth perovskite showing bandgap reduction and increment in device efficiency and opens up the possibilities towards compositional engineering for improved device performance. Graphic Abstract