Precise Control of Lead Halide and Ammonium Salt Stoichiometric Ratios for Efficient Perovskite Solar Cells

The precise stoichiometric ratio of lead halide and organic ammonium salts is a fundamental yet unresolved scientific challenge in perovskite solar cells (PSCs). Conventional deposition techniques fail to establish a definitive structure-performance relationship due to limitations in quantitative control, leading to inconsistent film quality and ambiguous reaction pathways. In this work, a precise quantitative deposition approach using drop-on-demand inkjet printing to systematically investigate the impact of organic salt deposition surface density on PSC performance is developed. The findings reveal that the deposition amount significantly affects the morphology, composition, and crystallinity of the perovskite films, influencing the overall device performance. Low deposition surface densities below 22 µg cm^-2 produce thin perovskite films with incomplete crystallization and small crystals, hindering charge carrier transport and separation. Conversely, a high deposition density (89 µg cm^-2) results in over-reaction between the organic salt and PbI₂, leading to low-quality perovskite films with pinholes, cracks, and poor interfacial contact. At the optimal deposition density of 39 µg cm^-2, it achieves high-quality perovskite films with large grains, reduced defects, and improved energy level alignment, resulting in a champion efficiency of 23.3% and improved environmental stability for the devices.