Investigation of the electronic and optical properties of unstrained and strained Ba3PCl3 antiperovskite using GW/BSE calculations

Abstract

Ba₃PCl₃ is a promising emerging antiperovskite material with potential applications in optoelectronics
and photovoltaics. In this study, we investigate the electronic and optical properties of the Ba₃PCl₃ using
many-body approaches, specifically the GW approximation and the Bethe-Salpeter equation (BSE). Using
the one-shot GW approximation, we observed a direct quasiparticle band gap of 1.99 eV for the unstrained
crystal. However, when the crystal was subjected to an isotropic compressive strain of up to 3%, while
retaining its direct band gap character, the band gap decreased significantly to 1.59 eV. Optical spectra
derived from the Bethe-Salpeter equation reveal pronounced excitonic peaks in the visible light region for
both unstrained and strained structures, with a systematic red shift observed as the compressive strain
increases. In addition, the excitonic binding energy decreases from 110 meV in the unstrained crystal to 50
meV at 3% compressive strain, indicating enhanced dielectric screening. Furthermore, we calculated the
spectroscopic limited maximum efficiency (SLME) to assess the photovoltaic performance of the crystal.
The results indicate a maximum efficiency of approximately 25% for the unstrained crystal, which increases
to approximately 32% under 3% compressive strain at a crystal thickness of ≥ 0.3 µm. This study shows
that strain engineering can effectively tune the electronic structure, optical properties, and photovoltaic
efficiency of Ba₃PCl₃, thereby supporting its viability as a lead-free solar absorber.