Investigations on the stability of the ambient processed bismuth based lead-free A3Bi2I9 (A = MA; Cs) perovskite thin-films for optoelectronic applications

Lead (Pb)-free bismuth (Bi) halide-based hybrid perovskites exhibit promising optoelectronic properties with low toxicity and air-stability. Fully ambient processed and high-quality perovskite thin-films are much desired for the industrialization of perovskite solar cells. So far, most of the lead-free perovskite halide thin films are processed and fabricated inside the glove box with ppm level atmosphere-controlled environment due to their poor stability. In this work, we report a one-step solution process employing solvent engineering to obtain highly crystalline and uniform (CH3NH3)3Bi2I9 (MBI) and Cs3Bi2I9 (CBI) perovskite thin-films prepared completely under ambient atmosphere. We further verified the stability of these MBI and CBI perovskite thin-films by exposing them to the ambient air with relative humidity and at room temperature for 180 days. The comparative structural, surface morphology and optical analysis of the samples show that bismuth halide perovskite can be an ideal candidate for fabrication in ambient atmosphere.