Band-Gap Tunability in Anharmonic Perovskite-Like Semiconductors Driven by Polar Electron-Phonon Coupling.

The ability to finely tune optoelectronic properties in semiconductors is crucial for the development of advanced technologies, ranging from photodetectors to photovoltaics. In this work, we propose a novel strategy to achieve such tunability by utilizing electric fields to excite low-energy polar optical phonon modes, which strongly couple to electronic states in anharmonic semiconductors. We conducted a high-throughput screening of over 10,000 materials, focusing on centrosymmetric compounds with imaginary polar phonon modes and suitable band gaps, and identified 310 promising candidates with potential for enhanced optoelectronic tunability. From this set, three perovskite-like compounds─Ag₃SBr, BaTiO₃, and PbHfO₃─were selected for in-depth investigation based on their contrasting band gap behavior with temperature. Using first-principles calculations, ab initio molecular dynamics simulations, tight-binding models, and anharmonic Fröhlich theory, we analyzed the underlying physical mechanisms. Our results show that polar phonon distortions can induce substantial band gap modulations at ambient conditions, including reductions of up to 70% in Ag₃SBr and increases of nearly 23% in BaTiO₃, relative to values calculated at zero temperature, while PbHfO₃ exhibits minimal change. These contrasting responses arise from distinct electron-phonon coupling mechanisms and orbital hybridization at the band edges. This work establishes key design principles for harnessing polar lattice dynamics to engineer tunable optoelectronic properties, paving the way for adaptive technologies such as wavelength-selective optical devices and solar absorbers.