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 (& AP;0.1 V). The absorbers must have high carrier concentration (1E20 cm(-3)) and low defect density (1E14 cm(-3)) to achieve these PCEs.