Theoretical Insights of Degenerate ZrS₂ as a New Buffer for Highly Efficient Emerging Thin‐Film Solar Cells

SnS, Sb₂Se₃, Cu₂SnS₃, CuSb(S,Se)₂, and Cu₂BaSn(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, ZrS₂ as an alternative buffer for the aforementioned emerging thin‐film solar cells using SCAPS‐1D is proposed. The important ZrS₂ parameters are optimized, including bandgap, thickness, carrier concentration, and defect density. Interestingly, ZrS₂ 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 ZrS₂ parameters optimization, the built‐in potential of SnS, Sb₂Se₃, Cu₂SnS₃, CuSb(S,Se)₂, and Cu₂BaSn(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, Sb₂Se₃, and CuSb(S,Se)₂ while >32% for Cu₂SnS₃ and Cu₂BaSn(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.