Modeling and performance optimization of two-terminal Cu2ZnSnS4-silicon tandem solar cells

A dual-junction Cu2ZnSnS4-Silicon (CZTS-Si)-based tandem configuration is modeled and analyzed for its viability as a solar cell. The top and bottom modules in the tandem structure are validated by comparison with experiment. Initially, the designed tandem structure yields very low efficiency of 3.18%, and the various loss mechanisms are identified and investigated. The current mismatch between top and bottom cells and parasitic absorption (photon losses) are suggested to be the major causes limiting the short circuit current and hence the efficiency of the device. We optimize the material parameters within experimentally achievable limits in order to obtain current matching, and the optimized thicknesses of copper zinc tin sulfide (CZTS) and silicon (Si) absorbers are found to be 150 nm and 250 mu m, respectively. The simulation results revealed that the photon losses are reduced, and overall absorption in the longer wavelength region has enhanced with the replacement of cadmium sulfide (CdS) by zinc sulfide (ZnS) buffer and careful optimization of the front layers of the device. The maximum predicted efficiency of tandem structure is >20% by minimizing the recombination centers within the experimentally obtainable ranges and improving the carrier separation process.

Automated summary

The study analyzes a dual-junction CZTS-Si tandem solar cell structure and identifies current mismatch and photon losses as the main factors limiting efficiency. Through optimization of material parameters and structure design, the predicted efficiency of the tandem structure can be significantly improved to over 20%.