Time-resolved fluorescence anisotropy study of organic lead halide perovskite

• Symmetry of perovskite structure affects fluorescence anisotropy.
• MAPbBr3 exhibits isotropic while MAPbI3−xClx (x≥0) exhibit anisotropic fluorescence.
• Fluorescence anisotropy dynamics depends on halide composition.
• Fluorescence anisotropy response is independent of fabrication process.
• Hole transport capping layer can accelerate the decay of the fluorescence anisotropy.

The photoluminescent polarization properties of organic halide perovskites are of great importance for the fundamental understanding and for device fabrication, while limited relevant work has been published. In this work we investigate the fluorescence polarization properties of the CH3NH3PbI3, CH3NH3PbI3−xClx, and CH3NH3PbBr3 perovskites which have been used in some of the highly efficient solar device to date. Time-resolved fluorescence anisotropy measurements were conducted on these perovskites fabricated by different methods, and with or without the capping hole transport layer. We demonstrate that CH3NH3PbBr3 perovskite exhibits isotropic fluorescence polarization while CH3NH3PbI3 and CH3NH3PbI3−xClx perovskites exhibit anisotropic fluorescence polarization. The composition influences significantly fluorescence anisotropy dynamics while fabrication has relatively weaker influence. The hole transport capping layer can accelerate the decay of the fluorescence anisotropy. The symmetry of perovskite structure is proposed to be the key factor to impact the fluorescence anisotropy.