NH₄I Facilitated the Formation of Mixed-Dimensional Perovskite and Improved Stability at Different Annealing Temperatures

Hybrid organic/inorganic perovskites as light absorption layer have received considerable attention because of their preeminent photovoltaic performance. Presently, gaining high power conversion efficiency (PCE) and long-term stability of perovskite solar cells (PSCs) is very crucial to achieve their practical application. Here, NH₄I was introduced to fabricate the mixed dimensional (MD) perovskite films at different annealing temperatures. The addition of NH₄I could improve the preferential crystal orientation within the polycrystalline, favor the formation of MD perovskite, and suppress the existence of yellow PbI₂ phase. The results indicate that MD perovskite films have a smoother surface, preferentially oriented perovskite crystal, and better optical properties at the same annealing temperature, compared with formamidinium (FA) perovskite. The MD perovskite device displays excellent photovoltaic performance possessing a high PCE of 18.93% at 100 °C. More importantly, the 1200 h humidity and 200 h heat stability tests reveal that the MD perovskite devices at optimized annealing temperature show great stability against moisture and heat. The findings are crucial to perovskite photovoltaics on improving the PCE and the long-term stability in industrialization and other applications.