Effect of Cl doping amount on the microstructure, photovoltaic properties and ferroelectric properties of Bi-based lead-free perovskite

Organic–inorganic hybrid perovskites with 3D perovskite structure have gained much attention as light harvesting materials in thin-film photovoltaics. This is because of their outstanding light-absorption characteristics, charge-transport dynamics and their simple processability using lab-scale solution and vapor phase deposition techniques. However, the inherent instability and lead toxicity of lead-based PSCs are the major problems at present. Recent studies have shown that the (CH3NH 3 ) 3 Bi2I9 (MBI) 0D bismuth-based compound can be used as an optical absorption layer in solar cells. In this paper, the (CH3NH 3 ) 3 Bi2I9 was doped with Cl− and a series of (CH3NH 3 ) 3 Bi2I 9 − x Clx films were prepared. The effects of different doping amounts on the microstructure, photovoltaic properties and ferroelectric properties were systematically investigated. Scanning electron microscope (SEM) and Atomic force microscope (AFM) analysis showed that with the increase of doping content, the density of the films increased and the roughness decreased. The photoelectric conversion efficiency of (CH3NH 3 ) 3 Bi2I 9 − x Clx raises with the increase of doping content. For example, the photoelectric conversion efficiency of (CH3NH 3 ) 3 Bi2I3Cl6 is 0.473%. We find that the leakage current descends into the increase in doping content, which may be due to the increase in the film density and the decrease of porosity. These research results have a positive effect on the development of Bi-based lead-free perovskite.