Hybrid Perovskites as White-Light Phosphors and Solar-Cell Absorbers

Hemamala Karunadasa, Department of Chemistry, Stanford University, California, USA

We use organic cations to direct the assembly of two-dimensional inorganic structures in crystalline, hybrid materials. We have recently synthesized families of layered perovskites that emit radiation across the entire visible spectrum (similar to sunlight) upon near-ultraviolet excitation. They are promising as phosphors for solid-state lighting. The broadband emission allows for accurate representation of illuminated colors and the chromaticity of the emission can be tuned through synthetic chemistry to afford both “warm” and “cold” white light. Unlike most inorganic phosphors that are synthesized at high temperatures, the organic molecules allow us to form these materials in solution under ambient conditions. Importantly, emission arises from the bulk material and not from surface defect sites. I will present our mechanistic studies that indicate strong coupling between photogenerated excitons and the lattice. This can lead to broad photoluminescence due to radiative decay from distorted excited states.

The three-dimensional hybrid perovskite (CH₃NH₃)[PbI₃] has recently been identified as a promising absorber for solar cells. Though remarkable progress has been achieved in efficiencies of devices containing these absorbers, the moisture sensitivity of the material remains a problem for large-scale device fabrication and their long-term use. I will present our recent results on structural modifications that improve the moisture stability of these materials and provide additional routes for tuning the properties of these versatile and well-defined materials.