Tunneling layer for lowering recombination and efficiency enhancement in CZTS solar cell

The performance of Cu₂ZnSnS₄ (CZTS) solar cells is often constrained by high interface recombination and defect states at the absorber/buffer interface, which hinder charge carrier extraction and reduce efficiency. In this work, we propose and analyze the incorporation of a tunneling layer between the CZTS absorber and the buffer layer to mitigate these losses. Through numerical simulations, we investigate the impact of the tunneling layer on device performance. The results reveal that the tunneling layer significantly suppresses interface recombination, lowers defect density, and enhances photogenerated carrier collection. A comparative study shows an improvement in Voc from 0.79 V to 1.22 V, FF from 69.47 % to 89.68 %, and efficiency from 12.61 % to 24.83 %. These findings demonstrate that strategic implementation of a tunneling/passivation layer can be a simple yet effective method to boost the efficiency of earth-abundant and environmentally friendly CZTS solar cells, bringing them closer to commercial viability.