Photovoltaic properties of ABSe₃ (A = Ca, Sr, Ba; B = Zr, Hf) chalcogenide perovskites

Chalcogenide perovskites have emerged as promising materials for optoelectronic applications due to their stability, non-toxicity, narrow bandgaps, high absorption, and excellent tolerance to defects. However, studying their excitonic and polaronic properties has been limited because of the high computational cost. In this study, we systematically analyzed the electronic, optical, transport, excitonic, and polaronic properties of chalcogenide perovskites ABSe₃ (A = Ca, Sr, Ba; B = Zr, Hf) in their needle-like (α-phase) and distorted (β-phase) forms using advanced computational methods like DFT, DFPT, GW, and BSE. Our findings confirm the stability of these materials and show that they have direct electronic bandgaps between 1.02 and 1.97 eV, as well as low charge carrier masses, indicating good mobility. Optical analysis reveals a high absorption coefficient, with β-phases absorbing light in the visible range. The smaller exciton binding energies (0.02–0.10 eV) and longer exciton lifetimes in the β-phases further enhance their optoelectronic performance. Moreover, intermediate electron-phonon coupling leads to high polaronic mobility, surpassing sulfur-based alternatives. Polaron energy calculations show that the α-phase supports more stable bound excitons, while the β-phase favors charge-separated polaronic states. These properties make β-ABSe₃ ideal candidates for eco-friendly, efficient solar cells, with predicted efficiencies ranging from 17.5% to 23%.