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 %.