Thermodynamic Origin of the Photostability of the Two-Dimensional Perovskite PEA2Pb(I1-XBrX)4

The two-dimensional (2D) mixed halide perovskite PEA2Pb(I1-xBrx)4 exhibits high phase stability under illumination as compared to the three-dimensional (3D) counterpart MAPb(I1-xBrx)3. We explain this difference using a thermodynamic theory that considers the sum of a compositional and a photocarrier free energy. Ab initio calculations show that the improved compositional phase stability of the 2D perovskite is caused by a preferred I-Br distribution, leading to a much lower critical temperature for halide segregation in the dark than for the 3D perovskite. Moreover, a smaller increase of the band gap with Br concentration x and a markedly shorter photocarrier lifetime in the 2D perovskite reduce the driving force for phase segregation under illumination, enhancing the photostability.

Automated summary

The two-dimensional mixed halide perovskite PEA2Pb(I1-xBrx)4 exhibits higher phase stability under illumination compared to the three-dimensional counterpart MAPb(I1-xBrx)3. The improved compositional phase stability is attributed to the preferred I-Br distribution in the 2D perovskite, resulting in a lower critical temperature for halide segregation in the dark. Additionally, the smaller increase of band gap with Br concentration and shorter photocarrier lifetime in the 2D perovskite reduce the driving force for phase segregation under illumination, enhancing the photostability.