Pressure‐Induced Emission Enhancement, Band‐Gap Narrowing, and Metallization of Halide Perovskite Cs₃Bi₂I₉

Abstract

Low-toxicity, air-stable bismuth-based perovskite materials are attractive substitutes for lead halide perovskites in photovoltaic and optoelectronic devices. The structural, optical, and electrical property changes of zero-dimensional perovskite Cs Bi I resulting from lattice compression is presented. An emission enhancement under mild pressure is attributed to the increase in exciton binding energy. Unprecedented band gap narrowing originated from Bi-I bond contraction, and the decrease in bridging Bi-I-Bi angle enhances metal halide orbital overlap, thereby breaking through the Shockley-Queisser limit under relatively low pressure. Pressure-induced structural evolutions correlate well with changes in optical properties, and the changes are reversible upon decompression. Considerable resistance reduction implies a semiconductor-to-conductor transition at ca. 28 GPa, and the final confirmed metallic character by electrical experiments indicates a wholly new electronic property.

Pressure‐Induced Structural Evolution and Bandgap Optimization of Lead‐Free Halide Double Perovskite (NH4)2SeBr6

“…As suggested, the bandgap of perovskite materials is highly variable based on the overlap of electronic wave functions between metal B and halide X ions . Figure a shows the first‐principles DFT calculated bandgap versus pressure.…”

Electrical Transport Properties of Gallium Phosphide under High Pressure

“…By contrast, increasing the temperature for metals enhances the lattice vibrations and increases the probability of electron scattering by phonons, causing decreased conductivity . Therefore, the semiconductor‐to‐metal transition can be determined from the temperature dependence of the resistance/resistivity . The resistance of GaP decreases with increasing temperature when the pressure is below 24.6 GPa, which coincides with the behavior of the electrical conductivity for a semiconductor (Figure a).…”

Bismuth Halide Perovskite‐Like Materials: Current Opportunities and Challenges

“…Considering the wide band gap of Cs 3 Bi 2 I 9 is a major factor for low PCE, we tried to improve their optical and electrical properties by lattice compression . With increasing pressure, the absorption edge continually redshifts along with an extraordinary piezochromic transition from the initial transparent bright red to opaque black above around 9.0 GPa (Figure a, b).…”