Concurrent Design of Alloy Compositions of CZTSSe and CdZnS Using SCAPS Simulation: Potential Routes to Overcoming VOC Deficit

Solar energy is the most used renewable energy source. CZTSSe uses earth-abundant elements and has promising optoelectronic properties, resulting in becoming a viable alternative to thin film PV. This work provides design guidelines for CZTSSe-based solar cells, where CZTSSe has a tunable affinity and energy gap. The analysis is based on incorporating a ternary compound material to serve as an electron transport material (ETM). In this regard, CdZnS is a potential candidate that can be utilized as an electron transport layer whose affinity and energy gap can be tuned to adjust the band alignment at the ETL/CZTSSe interface. In order to design a high-efficiency solar cell, one has to tune both the ETL and absorber layers to have a suitable conduction band offset (CBO), thereby minimizing the non-radiative recombination which, in turn, boosts the power conversion efficiency (PCE). Thus, in our presented simulation study, we provide a codesign of alloy compositions of both the CZTSSe photoactive layer and the CdZnS ETL using SCAPS-1D simulation. It is found that using the codesign of alloy compositions of the ternary compound ETL and the absorber enhances the PCE by about 2% and, more importantly, overcomes the main issue in CZTSSe which is its open-circuit voltage (VOC) deficit. Furthermore, upon optimizing the thickness and doping of both the ETL and absorber layer, as well as the bulk defect of the absorber layer, a PCE of 17.16% is attained in this study, while the calibrated PCE based on a previously published experimental work was 12.30%.