Efficiency improvement of CIGS solar cells with ZnSe buffer layer and SnS BSF layer

Abstract

Copper indium gallium selenium (CIGS) solar cells have attracted significant attention, owing to their high efficiency, flexibility, and cost-effectiveness. Their direct bangap and significant optical absorption coefficient of about 10⁵ cm⁻¹ make them particularly promising for photovoltaic applications. This study presents an extensive numerical analysis using SCAPS-1D software, systematically evaluating buffer layers (CdS, In₂S₃, ZnS, ZnSe) and back surface field (BSF) layer materials (PbS, SnS, CuTe₂) to optimise performance. Unlike previous studies focusing on individual materials, our comprehensive approach reveals critical insights into layer interactions through comparative analysis. SnS emerged as the most effective BSF material, achieving an open-circuit voltage of 0.815 V and an efficiency of 26.75 % when paired with ZnSe as the buffer layer. This is due to the BSF's ability to minimise back-surface recombination and enhance carrier collection. This result is also attributed to ZnSe's better band alignment with the CIGS layer, which reduces interface recombination and enhances device performance. Additionally, reducing The CIGS layer thickness from 3 μm to 2.2 μm decreases material usage and costs, with minimal impact on efficiency when ZnSe and SnS are used. This combination ensures high efficiency and reduced toxicity. In the second set of investigations, we optimise the absorber, buffer, and BSF layer thicknesses and the doping concentrations by analysing the short-circuit current density, open-circuit voltage, fill factor, and efficiency of the CIGS solar cell. The results show a high efficiency of 33.70 % for layer thicknesses of ZnSe, CIGS, and SnS of 40 nm, 2.2 μm, and 50 nm, respectively, and doping concentrations of the order of 10¹⁶, 1.65 × 10¹⁹, and 10¹⁶ cm⁻³, respectively. We also investigate the effects of defect densities within the CIGS, ZnSe, and SnS layers, as well as the CIGS/ZnSe and CIGS/SnS interfaces. Defects in both the bulk and at interfaces degrade the performance of the solar cells. Finally, we study the effect of temperature variations on solar cell performance. An increase in temperature contributes to efficiency degradation. This innovative structure, Mo/SnS/CIGS/ZnSe/ZnO, can be used to develop low-cost, sustainable, and eco-friendly high-efficiency CIGS solar cells.