Investigation of the Optical and Electrical Properties of ITO/ZnO/CdS/CuO:Co/Ag Structure for Solar Cell

Abstract

In this work, a new structure ITO/n-ZnO/n-CdS/p-CuO:Co/Ag for solar cell was prepared on a glass/ITO substrate. The RF sputtering was used to deposit the window layer (n-ZnO) at different time periods in order to reach various thickness of this film. The n-CdS thin films were synthesized by sol-gel technique to reduce the energy bands. The buffer layer (p-CuO:Co) was sputtered at 200 W, under 30% of oxygen. Then, the electrode (Ag) with a thickness of 100 nm was deposited by thermal evaporation under a pressure of 10-5 mbar. The photovoltaic activity results obtained from this structure showed that the above method is more relevant to achieve such structure. The electrical properties of this structure were investigated using the current-voltage (I-V) and AC impedance complex measurements. The values of open circuit voltage (Voc), short-circuit current (Jsc), and fill factor (FF) are 0.46 V, 4.1 mA cm-2, and 30%, respectively. The analysis of complex impedance measurements was very useful to investigate the electrical behavior of n-ZnO/n-CdS and n-CdS/p-CuO:Co interfaces. The impedance data are presented in the Nyquist and Bode plots at different thicknesses of the n-ZnO films. An equivalent circuit was used to analyze and to fit the experimental data. The validity of these fitting results is further supported by the extrapolation and the deconvolution of both process of the diffusion and recombination processes at the n-ZnO/n-CdS and n-CdS/p-CuO:Co interfaces, respectively. Our finding could provide an efficient method for fabricating a new configuration for improving the efficiency of inorganic ZnO/CuO solar cells as well as a useful approach for the analysis of complex impedance measurements. Further works are in progress in order to better improve the conversion efficiency.