High photoactive black phase stability of CsPbI3 nanocrystals under damp-heat conditions of 85 °C and 85% relative humidity

Abstract

CsPbI₃ as a newly emerging semiconductor material has displayed tremendous prospects for optoelectronic applications. However, the poor photoactive black-phase stability limits its further application. In this work, we introduce transition metal nickel ion (Ni²⁺) as a B-site substitute into CsPbI₃ nanocrystals (NCs) to stabilize their black phase. The optimized CsPbI₃ NCs film presents a record photoactive black-phase stability time of 54 hours under the conditions of 85 °C and 85% relative humidity, over 108 times that of the undoped film. Furthermore, the Ni²⁺-doped CsPbI₃ NCs solutions maintain bright red emission after vigorous stirring with an equal volume of water for 200 hours (the undoped solution is almost completely quenched), and also show bright red emission after being stored in the air for 200 days (the undoped solution is completely quenched within 43 days). Meanwhile, the photoluminescence quantum yield increased from 31.48% for undoped CsPbI₃ NCs to 87.69% for doped Ni-3.65% CsPbI₃ NCs. We suggest that these outstanding stabilities and excellent optical properties can mainly be attributed to the increased defect formation energy after rational Ni doping and lattice adjustment by partial replacement of Pb²⁺ with small-sized Ni²⁺. Our work provides guidance for the synthesis of phase-stabilized CsPbI₃ NCs and an insight into the effect of B-site doping in a perovskite lattice, providing a promising pathway to construct stable and efficient photoelectronic devices.