Dynamic Symmetry Conversion in Mixed-Halide Hybrid Perovskite upon Illumination

Organic-inorganic hybrid halide perovskites (ABX(3), where A = CH3NH3+ (methylammonium ion, MA); B = Pb2+; and X = Br-, I-, or Cl-) have excellent optoelectronic properties and are highly efficient photovoltaic materials, but their chemical instability impedes their development for use in next-generation solar cells, wherein they serve as the light-harvesting material. Here, we propose a mechanism of photoluminescence red-shift, a performance-loss phenomenon known as light-induced halide segregation, in mixed-halide perovskites upon illumination using in situ single-particle spectroscopy and synchrotron-based X-ray techniques. Our experimental analyses suggest a defect-assisted photoinduced transition from ordinary nonpolar phases to polar phases at the local scale within seconds is coupled with organic cation reorientation, which in turn narrows the bandgap; first-principles calculations quantitatively supported this result. Our findings provide deeper insights into the nature of local polar domains in hybrid perovskite materials and help improve device stability and efficiency.

Automated summary

The study reveals the photoluminescence red-shift phenomenon in organic-inorganic hybrid halide perovskite materials under illumination, leading to performance loss due to light-induced halide segregation. Experimental results show that defect-assisted photoinduced transition from nonpolar to polar phases at the local scale in mixed-halide perovskites, coupled with organic cation reorientation, results in bandgap narrowing.