Theoretical Insights of Degenerate ZrS ₂ as a New Buffer for Highly Efficient Emerging Thin‐Film Solar Cells

Abstract

SnS, Sb ₂Se ₃, Cu ₂SnS ₃, CuSb(S,Se) ₂, and Cu ₂BaSn(S,Se) ₄ are emerging as promising light absorbers for thin‐film photovoltaics due to their extraordinary optoelectronic properties. However, improper band alignment with the buffer and large open‐circuit voltage ( V _OC) deficit limits their power conversion efficiencies (PCE). Therefore, finding a suitable buffer that overcomes these obstacles is crucial. Herein, ZrS ₂ as an alternative buffer for the aforementioned emerging thin‐film solar cells using SCAPS‐1D is proposed. The important ZrS ₂ parameters are optimized, including bandgap, thickness, carrier concentration, and defect density. Interestingly, ZrS ₂ behaves as a degenerate semiconductor at carrier concentrations >1E17 cm ⁻³, improving the conductivity of the solar cells; it also demonstrates a high defect tolerance nature when the defect density lies between 1E12 and 1E18 cm ⁻³. After ZrS ₂ parameters optimization, the built‐in potential of SnS, Sb ₂Se ₃, Cu ₂SnS ₃, CuSb(S,Se) ₂, and Cu ₂BaSn(S,Se) ₄ solar cells is enhanced by 0.2, 0.58, 0.05, 0.42, and 0.3 V, respectively, reducing recombination rate. Upon optimizing absorbers parameters, a PCE > 35% for SnS, Sb ₂Se ₃, and CuSb(S,Se) ₂ while >32% for Cu ₂SnS ₃ and Cu ₂BaSn(S,Se) ₄ solar cells is accomplished with low V _OC loss (≈0.1 V). The absorbers must have high carrier concentration (1E20 cm ⁻³) and low defect density (1E14 cm ⁻³) to achieve these PCEs.