Thin-film solar cells of thermally evaporated antimony sulfide selenide absorbers with ZnS–CdS window layers

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Abstract Characteristics of solar cells of antimony sulfide selenide thin-film absorbers produced by vacuum thermal evaporation with chemically deposited ZnS/CdS window layers are presented. The solar cell, SnO2:F (FTO)/ZnS/CdS/Sb2S0.44Se2.56/C (Cell-A) with ZnS(50 nm)/CdS(65 nm) window layers and Sb2S0.44Se2.56 (450 nm), has shown an open circuit voltage (V OC) of 0.435 V, a short-circuit current density (J SC) of 32.9 mA cm–2, and a conversion efficiency (η) of 7.36%. For a cell with only a CdS film of 100 nm thickness as the window, SnO2:F(FTO)/CdS/Sb2S0.44Se2.56/C (Cell-B), these parameters are lower: V OC, 0.415 V, J SC 31.2 mA cm–2, and η, 6.8%. The addition of a ZnS thin film 50 nm in thickness along with the reduction in the CdS film thickness from 100 to 65 nm in Cell-A contributed to the increase in V OC and J SC. Analysis of the dark current in these cells showed the saturation current density (J 0) of Cell-A as 6 × 10–5 mA cm–2 with an ideality factor (n) of 1.62, and that of Cell-B as 5 × 10–4 mA cm–2 with n of 1.76. The built-in voltage of the junctions, obtained from their capacitance (C)—voltage (V) characteristics were 0.495 V for Cell-A and 0.463 V for Cell-B. The majority carrier (hole) concentration in the Sb2S0.44Se2.56 absorber was 5–9 × 1015 cm−3. Overall, the replacement of the CdS window with ZnS/CdS improved the antimony sulfide selenide solar cell. X-ray diffraction and x-ray photoelectron spectroscopy results suggest that the ZnS/CdS window produced at a substrate temperature of 450 °C in the cell structure may indeed be ZnS (3.7 eV)/ZnxCd1-xS (3.7–2.6 eV)/CdS (2.6 eV). In the electrochemical impedance measurements, a reduced charge recombination at the window/absorber interface was observed for the cell with the ZnS/CdS window.

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