Below 200 °C Fabrication Strategy of Black‐Phase CsPbI<sub>3</sub> Film for Ambient‐Air‐Stable Solar Cells
Tao Ye, Bo Zhou, Fei Zhan, Fangli Yuan, Seeram Ramakrishna, Dmitri Golberg, Xi Wang
Abstract
Cesium‐based fully inorganic black‐phase (BP) lead halide perovskites (such as α‐, β‐, and γ‐CsPbI 3 ) with excellent thermal stability and a decently high photovoltaic performance have attracted increasing attention. However, a below 200 °C fabrication process of the desirable BP CsPbI 3 has rarely been reported. Herein, the detailed crystal structure evolution of ambient‐air‐stable BP CsPbI 3 prepared under low temperature conditions is investigated by exploiting the strong coordination bonding between CO in polyvinylpyrrolidone (PVP) and Pb in CsPbI 3 and inflection effect of PVP under annealing. It is found that ambient‐air‐stable BP CsPbI 3 films are formed and the energy barrier for the long‐term stable BP CsPbI 3 formation is significantly reduced (the required annealing temperature is only 80 °C). After optimization, the highest power conversion efficiencies (PCEs) of ≈4.0% and 10.0% are recorded for the 3% PVP‐added devices with light absorbers annealed at 80 and 160 °C, respectively. More importantly, the 3% PVP device annealed at 160 °C maintains ≈80% of its original PCE after 5 months storage under ambient‐air conditions.