Design of High-Efficiency and Environmentally Stable Mixed-Dimensional Perovskite Solar Cells Based on Cesium-Formamidinium Lead Halide Component

Long-term instability of the high-efficiency perovskite solar cells (PSCs) has been the intractable hindrance for their further commercialized applications. Here, we successfully introduced 2-hydroxyethylamine cation (HEA + ) into Cs/FA mixed-cation three-dimensional (3D) perovskite to form a new-type stable mixed-dimensional (MD) perovskite structure based on the general formula of (HEA) 2 (Cs 0.1 FA 0.9 ) n −1 Pb n I 3 n +1 . The FAPbBr 3 component was also employed to improve the quality of the thin films. The designed MD perovskite films exhibit better crystallization, outstanding optical properties, and uniform morphology with fewer grain boundaries. Especially, because of inheriting the advantages of high-performance FA-based 3D perovskite, the PSCs made from MD-Br 10 ( n = 30) perovskite achieved the optimal power conversion efficiency (PCE) as high as 19.84% and an average PCE of 19.02% among 30 devices. Surprisingly, it is found that the MD PSCs show superior long-term stability when exposed to heat and moisture because of the high-quality films and intrinsic stability structure. After they were aged at the condition of 85 °C (about 10% relative humidity in the dark) for 400 h and 55 ± 5% relative humidity (about 25 °C in the dark) for 2160 h, the unencapsulated devices can maintain 82% and 87% of the initial PCE, respectively. This work provides a feasible design direction of new-type MD perovskites to obtain efficient and stable PSCs for next-generation photovoltaic devices.