Reversible degradation-assisted interface engineering via Cs4PbBr6 nanocrystals to boost the performance of CsPbI2Br perovskite solar cells

Abstract

CsPbI2Br perovskites are promising candidates for photovoltaic applications owing to the trade-off between the optoelectronic properties and phase stability of cesium-based inorganic perovskites. However, the major shortcomings of CsPbI2Br perovskite solar cells (PSCs), namely energy loss and poor moisture resistance, still need to be addressed. In this work, reversible degradation-assisted decoration with Cs4PbBr6 nanocrystals (NCs) is used to passivate the perovskite/hole transporting material (HTM) interface. Moisture-induced Cs4PbBr6 decomposition products (CsPbBr3 and CsBr) and CsPbI2−xBr1+x (x > 0), generated as a result of halide anion exchange between CsPbI2Br and Cs4PbBr6 or its decomposition products, are found to improve the quality of the CsPbI2Br film and suppress the trap state density. In addition, the decoration achieves desirable energy-level alignments at the CsPbI2Br/HTM interface and raises the Fermi level of the CsPbI2Br film, thereby strengthening the built-in electric field between the perovskite and HTM. As a result, the optimized CsPbI2Br PSC has a champion efficiency of 15.52% with an open-circuit voltage of 1.30 V (mean value: 1.29 V). The unencapsulated CsPbI2Br film and device both exhibit high air stability (∼40% humidity), and the latter retains 90% of its initial efficiency after a 500 h aging test.