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

CsPbI 2 Br 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 CsPbI 2 Br perovskite solar cells (PSCs), namely energy loss and poor moisture resistance, still need to be addressed. In this work, reversible degradation-assisted decoration with Cs 4 PbBr 6 nanocrystals (NCs) is used to passivate the perovskite/hole transporting material (HTM) interface. Moisture-induced Cs 4 PbBr 6 decomposition products (CsPbBr 3 and CsBr) and CsPbI 2− x Br 1+ x (x > 0), generated as a result of halide anion exchange between CsPbI 2 Br and Cs 4 PbBr 6 or its decomposition products, are found to improve the quality of the CsPbI 2 Br film and suppress the trap state density. In addition, the decoration achieves desirable energy-level alignments at the CsPbI 2 Br/HTM interface and raises the Fermi level of the CsPbI 2 Br film, thereby strengthening the built-in electric field between the perovskite and HTM. As a result, the optimized CsPbI 2 Br PSC has a champion efficiency of 15.52% with an open-circuit voltage of 1.30 V (mean value: 1.29 V). The unencapsulated CsPbI 2 Br 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. [Display omitted] • Decoration with Cs 4 PbBr 6 nanocrystals and subsequent reversible degradation. • The decoration improves crystal quality and suppresses trap state density. • Strengthening of the built-in electric field are also achieved by the decoration. • PSC V OC and moisture stability are simultaneously improved. [ABSTRACT FROM AUTHOR]