Effect of Cd1-xZnxS Window Layer Incorporation in CdTe Solar Cell by Numerical Simulation

Abstract

CdTe is a very potential binary semiconductor material for solar photovoltaic application due to its superior optoelectronic properties. The overall performances of incorporating Cd1-xZnxS window layer in lieu of CdS layer in CdTe solar cell were investigated by SCAPS-1D simulator. The Cd1-xZnxS is an alloy of CdS and ZnS which increase band gap of window layer from 2.42 eV to 3.7 eV as a function of x (from x=0 to 1). The spectral response of the design Cd1-xZnxS/CdTe cell improves in blue region which implies the big improvement of short circuit current density Jsc. In addition, in the traditional back contact of CdTe cell a small positive conduction band (ΔEC <0.3 eV) offset is necessary to reduce the forward current J0 as well as the recombination losses at the back contact. To achieve this goal a highly doped ZnTe:Cu extra layer was used as an electron reflector (ER) above back contact. Furthermore, this ER interface allows electron tunnelling by reducing the barrier height of the valence band which in turn leads to an improvement of open circuit voltage and fill factor. The performance of the proposed cell was examined by varying thickness and doping concentration of transparent conducting oxide (TCO) layer, window layer, absorber layer and finally ER layer. The simulated results of the proposed cell had shown that the open circuit voltage (Voc) overcame the 1-volt barrier of CdTe cell with energy conversion efficiencies of 19.93 %.