Tailoring Optoelectronic Characteristics of β-Ga ₂ O ₃ and ε-Ga ₂ O ₃ for Photovoltaic Cells

Gallium oxide is an ultrawide band gap semiconductor, which makes it very interesting for use in power electronics. Among its five polymorphs, β-Ga2O3 and ε-Ga2O3 have unique optoelectronic properties that make them suitable for use in semiconductors. β-Ga2O3 has a band gap of 4.4 eV, and doping increases its conductivity in the p-type. On the other hand, ε-Ga 2O3 has a band gap of 4.68 eV. Herein, using first-principles calculations, metal dopants have a significant effect on the absorption coefficient and cause the absorption peaks to shift. Codoping with metal and Se at 5.26% increases the absorption coefficient by adding impurity states. Interestingly, codoping with Mn + Se and Eu + Se increases absorption in the near-infrared spectrum, whereas codoping with Sn + Se reveals a prominent peak at 2.65 eV due to σ–π transition states. As a donor, Sn increases conductivity in photovoltaic charge transfer and the concentration of free carriers, potentially enhancing visible light absorption. The absorption spectrum of ε-Ga2O3 is more uniform due to d–d and f–f transitions, although β-Ga2O3 is more anisotropic. Furthermore, the kinetic Monte Carlo simulation shows that the band gap of β-Ga2O3 and ε-Ga2O3 decreases with increasing temperature. In β-Ga2O3, the highest efficiency for codoping Sn + Se ranges from 24–30%, while for ε-Ga2O3, it ranges from 22 to 27%. With the same dopants, this implies that β-Ga2O3 is a more favorable alternative for photovoltaic applications. Additionally, Sn doping significantly improves the performance of β-Ga2O3 solar cells, increasing their efficiency and durability while preserving their environmental friendliness. In addition to protecting the environment, this encourages renewable energy alternatives.