Characterisation of CuInS2/Zn(Se,O)/ZnO solar cells as a function of Zn(Se,O) buffer deposition kinetics in a chemical bath

Thin-film solar cells of CuInS2/Zn(Se,O)/ZnO configuration have been studied from the point of view of their dependence on the Zn(Se,O) chemical bath deposition (CBD) conditions. The kinetics of deposition of the Zn(Se,O) buffer is followed during cell processing with a quartz crystal microbalance (QCM). Two different CBD growth mechanisms yield buffer layers with different properties. Under a predominant electroless deposition reaction, the resulting buffer layer has mixed ZnSe-ZnO composition. The solar cells with this buffer type show higher fill factor (FF) and lower open-circuit voltage (V-oc). Under a chemical growth regime, the buffer layer has higher ZnSe proportion, giving rise to cells with higher V-OC, but lower FF and stability. The parameters of this second type of cell also show major dependence on illumination effects (light-soaking effects). Electron-beam-induced current (EBIC) and cathodoluminescence (CL) measurements are carried out to characterise the CuInS2/Zn(Se,O) junctions formed under the two buffer growth regimes. Cross-sectional EBIC shows a wider space charge region (SCR) than expected for p-CuInS2 in contact with Zn(Se,O), and the p-n junction is driven within the CuInS2 phase. These results reflect a chemical modification of CuInS2, most probably caused by the ammonia of the bath solution. CL shows more defective interfaces when Zn(Se,O) is deposited under the chemical mechanism (slower deposition rate, hence longer contact time of the CuInS2 with the bath solution) than under the electroless kinetics (faster deposition rate). Copyright (C) 2002 John Wiley Sons, Ltd.