Prospects of indium sulphide as an alternative to cadmium sulphide buffer layer in cis based solar cells from numerical analysis

Indium sulphide (In_xS_y) is a prominent candidate to be an alternative buffer layer to so-called toxic cadmium sulphide (CdS) in CIS based solar cells. In this study, buffer layer parameters layer thickness and buffer layer bandgap have been investigated by Solar Cell Capacitance Simulator (SCAPS) to find out the higher conversion efficiency. A promising result has been achieved with an efficiency of 16.76% (with V_oc = 0.610 V, J_sc = 34.63 mA/cm² and fill factor = 79.37) by using InXSy as a buffer layer. It is also found that the high efficiency of CIGS absorber layer thickness is between 1.5μm and 3μm. The bandgap of In_xS_y buffer layer was taken 2-2.9 eV to simulate which is related to the feasible value and In_xS_y bandgap is relatively higher compared to CdS buffer layer bandgap. Moreover, it is found that J_sc is very high for the buffer layer thickness of 30-50nm and quantum efficiency is almost 80% in 350-500 nm region attributed to less absorption of light in the buffer layer. In addition, it is revealed that the highest efficiency cell can be achieved with the buffer layer bandgap of 2.74-2.90 eV. This result can be explained in the practical work as non-stoichoimetric composition of indium sulphide may result in different bandgaps. Hence, a specific non-stoichoimetry composition which results in the highest bandgap is desirable to achieve high efficiency In_xS_y-CIGS solar cells. From the simulation results, numerous influences of buffer layer are investigated in CIGS solar cell which can lead to the fabrication of high efficiency devices.