The performance parameter of Cu₂ZnSnS₄ (Copper Zinc Tin Sulphide) based heterostructure solar cell have been studied by one dimensional solar capacitance simulator software program (SCAPS 1D). This software provides device performance based on layer by layer material properties. The proposed device structure Mo/ Cu₂ZnSnS₄ / CdS / ZnO integrates the properties such as non toxic, cost effective, environmental friendly and photovoltaic making them suitable for photovoltaic applications. The key structural parameters such as thickness, carrier concentration and doping were systematically varied to analyze the effect on device performance. To enhance the cell power efficiency optimization of the device and their key parameters has been performed. The effect of changing doping concentration and thickness of electron transport layer (ETL) and hole transport layer (HTL) has also been studied. The simulation study includes the comprehensive analysis of J-V characteristics, recombination mechanism, carrier density profiles, Quantum efficiency and I-V behavior under AM 1.5 spectrum illumination at 300 K temperature. By tuning these parameters, the optimized device structure demonstrates a significant improvement in photovoltaic performance. The simulated device has achieved power conversion efficiency (PCE) of 21 %. The result indicates the potential of CdS as an effective buffer layer in Cu₂ZnSnS₄ based solar cell in achieving high efficiency and stable solar devices.