Inhibiting octahedral tilting for stable <scp>CsPbI<sub>2</sub>Br</scp> solar cells
Aili Wang, Jianwei Wang, Xiaobin Niu, Chuantian Zuo, Feng Hao, Liming Ding
Abstract
Abstract The intrinsic phase instability of CsPbI 2 Br perovskite hinders its development and application in solar cells. Herein, we adopt 1‐butyl‐3‐methylimidazolium hexafluorophosphate (BMIMPF 6 ), a hydrophobic ionic liquid (IL), to improve the phase stability of CsPbI 2 Br. Density functional theory calculation reveals that the formation energy of CsPbI 2 Br with BMIMPF 6 is reduced, thereby restraining the [PbX 6 ] 4− octahedral tilting. The reduced structural distortion and relaxed lattice strain result in improved phase stability of CsPbI 2 Br. In addition, the interfacial dipole moment increases after introducing BMIMPF 6 , which facilitates the charge transfer. Consequently, the CsPbI 2 Br solar cells with BMIMPF 6 deliver a power conversion efficiency (PCE) of 16.2% along with excellent stability. The unencapsulated devices with BMIMPF 6 maintain 98.9%, 88.6%, and 99.5% of the initial PCEs after 1200 h storage in N 2 , 1000 h storage in air (30% relative humidity), and 200 thermal cycles (25–100°C), respectively. image