Theoretical design and performance evaluation of a lead-free fully inorganic CIGS solar cell with CuSbS2 as HTL

The widespread use of lead (Pb)-based materials in solar cells poses serious environmental and health risks, particularly through lead contamination. These hazards make the development of Pb-free alternatives a critical priority for safer and more sustainable photovoltaic technologies. This study addresses this pressing need by exploring innovative, non-toxic materials for high-efficiency solar cells. In response, this study introduces a novel, fully inorganic solar cell structure, FTO/ZnO/CIGS/CuSbS₂/Au, which leverages copper indium gallium (di) selenide (CIGS) as the absorber layer and copper antimony sulfide (CuSbS₂) as the hole transport layer (HTL). Our approach is distinguished by the strategic integration of zinc oxide (ZnO) as the electron transport layer (ETL), which, in conjunction with CuSbS₂, enhances charge transport efficiency and overall device performance. This research innovates by conducting a comprehensive numerical analysis to fine-tune critical parameters such as absorber layer thickness, doping levels, defect densities, and radiative recombination rates. By optimizing these parameters, we significantly improve the photoconversion efficiency of the solar cell. Additionally, we systematically investigate the influence of interface defects, metal back contacts, and temperature variations on device performance, providing new insights into the stability and efficiency of inorganic solar cells. A key mechanism explored in this study is the role of series and shunt resistances in determining the electrical behavior of the solar cell, analyzed through capacitance-voltage (C–V) and capacitance-frequency (C–F) measurements. These analyses reveal the intricate balance between charge carrier dynamics and external resistive factors, further elucidating the operational mechanisms within the cell. Our fully inorganic FTO/ZnO/CIGS/CuSbS₂/Au solar cell achieves a remarkable power conversion efficiency (PCE) of 32.25 % at room temperature, with a short-circuit current density (J_SC) of 34.77 mA/cm², an open-circuit voltage (V_OC) of 1.10 V, and a fill factor (FF) of 84.33 %. By comparing these results with both experimental and theoretical benchmarks in the field of CIGS solar cells, we demonstrate the competitive edge and profound significance of our lead-free design.