First-principles study on the physical properties of Al-based wide-bandgap perovskites Cs3AlIxBr6-x for optoelectronic applications

This study aims at exploring the potential of inorganic wide-bandgap mixed-halide aluminum-containing perovskites of Cs3AlIxBr6-x for solar harvesting, by investigating their structural, electronic and optical properties through density functional theory using the augmented plane wave plus local orbital method. The structural properties were calculated with the PBE-GGA potential. Volume optimization and negative formation energies confirm the structural and thermal stability of the compounds. The electronic and optical properties were calculated using Tran-Blaha modified Becke-Johnson (TB-mBJ) potential. The TB-mBJ corrected band gaps revealed that these materials belong to the wide-bandgap (WBG) perovskite family, displaying band gaps in the range of 3-5 eV. The electronic properties confirm their direct bandgap nature, with the I-p and Br-p states mainly contributing to the formation of the valence band and the Al-s, Al-p and Cs-d states to the conduction band. Absorption coefficients range from 10 to140 x 104 per cm in the UV region, thus making these WBG perovskites suitable for applications in this region. Optical properties show absorption of light beyond 3 eV and validate the calculated electronic band gaps. Absorption coefficients, optical conductivity and dielectric function (real and imaginary) were calculated and revealed a peak shift from higher to lower energies with increasing I concentration. The above results suggest that these materials can be highly considered for use in photovoltaics, optoelectronic devices (light-emitting diodes, photodiodes), to power small batteries in the Internet of Things, in agrivoltaics and in fabrication of semi-transparent solar cells.