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

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 (VOC) of 0.435 V, a short-circuit current density (JSC) of 32.9 mA cm–2, and a conversion efficiency (η) of 7.36%. For the 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: VOC, 0.415 V, JSC 31.2 mA cm–2, and η, 6.8 %. The addition of a ZnS thin film of 50 nm in thickness along with the reduction in the CdS film thickness from 100 nm to 65 nm in Cell-A contributed to the increases in VOC and JSC. Analysis of the dark current in these cells showed the saturation current density (J0) 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, 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 suggested 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 measurement, a reduced charge recombination at the window/absorber interface was observed for the cell with the ZnS/CdS window.