Numerical modeling of CZTS based heterostructured solar cell for high efficiency PV performance

This paper deals with the numerical performance evaluation of solar cells based on ZnMgO/CZTS with and without a back-surface field (BSF) layer. ZnMgO is used as a buffer layer due to its non-toxicity and strain-balancing properties at i-ZnO/ZnMgO and ZnMgO/CZTS interfaces. A multilayer structure of ZnO: Al/i-ZnO/ZnMgO/CZTS is considered for the initial analysis. Subsequently, a BSF layer of CZTS material with different optical and electronic properties, called CZTS2, is inserted between the back-contact layer and the existing CZTS layer, called CZTS1, to form a new structure as ZnO: Al/i-ZnO/ZnMgO/CZTS1/CZTS2 to enhance the performance. The performance of the structure with and without the BSF layer was evaluated in terms of various layer parameters such as thickness, band gap, carrier concentration, defect densities, and work function. Then, the effects of operating temperature and the combination of shunt and series resistance on the overall performance were investigated. The simulated results were calibrated with existing experimental data from the literature to validate the work. In the optimized structure with the BSF layer, a maximum efficiency of 23.67% is achieved, which is 4% higher than that of without the BSF layer. The generation and recombination rates of the structures with and without the BSF layer were investigated to understand the reason for the improved efficiency. The results of this work are very promising for the development of high-efficiency, low-cost, and non-toxic CZTS solar cells.