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

Abstract

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, SnO 2 :F (FTO)/ZnS/CdS/Sb 2 S 0.44 Se 2.56 /C (Cell-A) with ZnS(50 nm)/CdS(65 nm) window layers and Sb 2 S 0.44 Se 2.56 (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, SnO 2 :F(FTO)/CdS/Sb 2 S 0.44 Se 2.56 /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 Sb 2 S 0.44 Se 2.56 absorber was 5–9 × 10 15 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)/Zn x Cd 1-x S (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.