Strain-activated light-induced halide segregation in mixed-halide perovskite solids
Yicheng Zhao, Peng Miao, Jack Elia, Huiying Hu, Xiaoxia Wang, Thomas Heumueller, Yi Hou, Gebhard J. Matt, Andres Osvet, Yu‐Ting Chen, Mariona Tarragó, Dominique de Ligny, Thomas Przybilla, Peter Denninger, Johannes Will, Jiyun Zhang, Xiaofeng Tang, Ning Li, Chenglin He, Anlian Pan, Alfred J. Meixner, Erdmann Spiecker, Dai Zhang, Christoph J. Brabec
Abstract
Abstract Light-induced halide segregation limits the bandgap tunability of mixed-halide perovskites for tandem photovoltaics. Here we report that light-induced halide segregation is strain-activated in MAPb(I 1−x Br x ) 3 with Br concentration below approximately 50%, while it is intrinsic for Br concentration over approximately 50%. Free-standing single crystals of CH 3 NH 3 Pb(I 0.65 Br 0.35 ) 3 (35%Br) do not show halide segregation until uniaxial pressure is applied. Besides, 35%Br single crystals grown on lattice-mismatched substrates (e.g. single-crystal CaF 2 ) show inhomogeneous segregation due to heterogenous strain distribution. Through scanning probe microscopy, the above findings are successfully translated to polycrystalline thin films. For 35%Br thin films, halide segregation selectively occurs at grain boundaries due to localized strain at the boundaries; yet for 65%Br films, halide segregation occurs in the whole layer. We close by demonstrating that only the strain-activated halide segregation (35%Br/45%Br thin films) could be suppressed if the strain is properly released via additives (e.g. KI) or ideal substrates (e.g. SiO 2 ).