Investigation on lead-free Sc–Cu double perovskite based tandem solar cells: a 2T and 4T design approach

Abstract The tandem photovoltaics design can be used as a viable way of overcoming the Shockley–Queisser limit of photovoltaic cells via optimization of the light absorption spectrum and minimizing thermalization losses. This work presents the numerical analysis of a novel design of an alkali-based double perovskite tandem solar cell (ADPTSC), comprising lead-free absorbers, K 2 ScCuCl 6 and Cs 2 ScCuCl 6 , utilizing the SCAPS-1D software in standard AM 1.5G illumination conditions (1000 W m − 2 ). The ADPTSC structure is built of the FTO/ZnSe electron transport layer, alkali-based double perovskite absorbing layers, and SrCu 2 O 2 hole transport layer. Series-connected (2 T) and parallel-connected (4 T equivalent electrical configuration) tandem structures are considered in order to assess the effect of electrical configuration on the photovoltaic performance of this novel device. Besides the assessment of current density versus voltage characteristics of both series and parallel connected devices, other properties such as band alignment, quantum efficiency, defect density, temperature stability, impedance spectroscopy, and metals’ work function effect are also studied to determine the main limiting factors to performance enhancement. The series-connected structure showed promising performance parameters of an open-circuit voltage of 1.82 V, short-circuit current density of 21.65 mA cm − 2 , fill factor of 85.86%, and power conversion efficiency of 39.43%. Parallel-connected structure provided slightly lower open-circuit voltage, 0.79 V. However, it exhibited significantly higher short-circuit current density of 50.39 mA cm − 2 , leading to a fill factor of 80.55% and improved efficiency of 40.00%. It was found that parallel connection allows to reduce current mismatch problems and series connection enables voltage addition advantage.