High-efficiency CGS/CZTSSe tandem thin-film solar cells: a simulation-based study

Abstract Single-junction copper zinc tin sulfo-selenide (CZTSSe) solar cells typically face significant efficiency limitations due to substantial optical and recombination losses, hindering their practical deployment. To overcome these challenges, a novel, cadmium-free tandem thin-film solar cell architecture consisting of a copper gallium diselenide (CGS) top cell combined with an optimized CZTSSe bottom cell is proposed. Through meticulous bandgap engineering, doping concentration adjustment, and absorber layer thickness optimization, significant mitigation of both voltage and current losses is targeted. Using the SILVACO-TCAD toll, the effects of varying selenium molar ratio, doping density, absorber thicknesses, and operating temperature on device performance were systematically analyzed. This simulation demonstrates the prospective viability of this design, indicating an increase in power conversion efficiency (PCE) from an initial 25.01% to 34.26% under standard test conditions (300 K), with a peak efficiency of 37.18% at 270 K. These simulated improvements primarily result from enhanced long-wavelength absorption in the CZTSSe bottom cell and reduced carrier recombination in the CGS top cell. This design demonstrates promising potential; however, achieving practical high-performance devices will require further experimental validation, careful selection of electron and hole selective contact materials, interface engineering, and addressing scalability and durability challenges.