Fabrication of Sulfur-Incorporated Bismuth-Based Perovskite Solar Cells via a Vapor-Assisted Solution Process

Methylammonium (MA) bismuth iodide ((CH3NH3)(3)Bi2I9) is a promising perovskite material for solar cell application considering the air stability and the nontoxic lead-free molecular constitution. However, the further improvement of the device performances is prohibited by the wide bandgap (approximate to 2.1 eV) and unsatisfied crystallinity of the (CH3NH3)(3)Bi2I9 films. Herein, a developed low-pressure vapor-assisted solution process (LP-VASP) method is applied to obtain the sulfur-incorporated bismuth-based perovskites films. Due to the presence of sulfur, both the crystal quality and the energy band property are improved effectively in the as-fabricated lead-free perovskite films. After a systematic study of the influence of the reaction time on the device performances, the optimized reaction time is found to be 30 min, under which, the sulfur-incorporated MA(3)Bi(2)I(9-2x)S(x) perovskite films exhibit a reduced bandgap of 1.67 eV and a compact morphology. The corresponding optimal PCE reaches 0.152%. This study provides a new way for the incorporation of sulfur in the lead-free bismuth-based perovskite solar cells.