Influence of Post-Annealing on the Properties of Methylammonium Bismuth Iodide Perovskite Solar Cells Through the Hot Immersion Method

In this paper, the influence of post-annealing on the properties of methylammonium bismuth iodide (MBI) perovskite solar cells (PeSCs) fabricated through the hot immersion method (HIM) is reported. The post-annealing temperature varied between 100 degrees C and 250 degrees C. The XRD results showed that the crystallinity of the MBI film was improved, while the surface morphology showed that the flake-shaped structure was enhanced. On increasing the post-annealing temperature, an increase in the average grain size from 0.9 mu m to 3 mu m was observed. The increase in the grain size led to an enhancement of the optical properties with a narrower indirect bandgap at an extended absorption region towards a longer wavelength. Eventually, the performance of HIM-fabricated MBI PeSCs showed a twofold increase, i.e., from 0.14 V to 0.28 V, for open-circuit voltage, the short-circuit current density of the device increased by more than twofold, and power conversion efficiency increased up to 0.011% with a fivefold increase at 250 degrees C. An improved morphology and enlarged grain size leads to a drastic increase in the efficiency of the devices. Our findings suggest that by using HIM, the performance of MBI solar cells can be improved by post-annealing, providing an alternative, simple method for the fabrication of Pb-free PeSCs in future work. [GRAPHICS] .