Achieving stable and high-efficiency (>21%) lead halide perovskite solar cells with δ-CsPbI2Br seed–assisted growth strategy

Abstract

Recently, mixed cation-halide perovskites have become particularly interesting for high-performance perovskite solar cells (PSCs) owing to their near-ideal bandgap. Nevertheless, mixed cation-halide perovskites prepared via the existing methods are often subject to high defect density and poor stability, especially the sequential deposition methods in view of the difficulty of incorporating cesium cations (stabilizer). Herein, a simple and effective approach of δ-CsPbI2Br seed–assisting sequential deposition is developed. It is revealed that introducing δ-CsPbI2Br seeds into PbI2 film could not only effectively incorporate Cs+ into the mixed cation-halide perovskite film but also afford δ phase crystal lattices to promote the growth of α phase perovskites during annealing. Such a process can prepare high-quality perovskite film with larger grain size, lower defect density, and longer photoluminescence carrier lifetime (1658 ns). In addition, the thermal stability and humidity stability of the perovskite film are significantly boosted. Consequently, the optimized device delivers a champion efficiency of 21.62%, with an average efficiency of 1.5% higher than that of the control device. In addition, the unencapsulated device exhibits remarkable operational stability, retaining ~92% of the initial efficiency after aging for 1000 h in ambient air. This work provides insight for further preparing the high-quality perovskite film and improving the performance of PSCs.