In the rapid growth of thin film solar cells, Cu2ZnSnS 4 (CZTS) poses to be a potential and alternative absorber layer of CIGS based cells. Besides solving the scarcity issue of rare materials like In or Ga in CIGS based solar cells, the CZTS based cells do not contain any toxic material and can lead to produce nontoxic thin film solar cells with excellent optical properties. In this work, absorber layer parameters have been studied by Solar Cell Capacitance Simulator (SCAPS) in terms of CZTS layer thickness and band gap to find out the optimum electrical performance. A promising result has been achieved with an efficiency of 7.55 % (with Voc = 0.5136 V, Jsc = 30.83 mA/cm2 and fill factor = 47.65 %) by using CZTS/CdS structure. It has also been found that the high efficiency of CZTS absorber layer thickness lies between 1 and 2.2 μm. This result can be explained in the practical work as non-stoichiometric composition of CZTS may result in lower efficiency of the solar cells. Quantum efficiency is almost 80% in the region of 350-500 nm, due to less absorption of light in the buffer layer. In addition, it is revealed that the highest efficiency cell can be achieved with the In2S3 buffer layer band gap of 2.74-2.90 eV. The study suggests that the proposed solar cell can be widely exploited in response to the fabrication of high efficiency thin film photovoltaic devices.