Boron-Modified Heterointerface Boosts Kesterite Solar Cells to 0.58 V Open-Circuit Voltage

Achieving high open-circuit voltage (V_OC) continues to pose a significant challenge for kesterite Cu₂ZnSn(S,Se)₄ (CZTSSe) solar cells, predominantly due to the pronounced charge carrier recombination occurring at heterointerface (HEI). To address this issue, an innovative non-metallic boron (B)-modification strategy is developed to optimize the HEI. The key advantages of this strategy are as follows: (i) Leveraging the strong bonding characteristic of B with three valence electrons, the dangling bonds on the absorber surface can be fully saturated, effectively passivating surface states without introducing new defects; (ii) Moreover, diffusion of B into the near-surface region of HEI during selenization process can create weak n-type B_Cu donor defects, which lowers the valence band maximum (VBM) of the absorber and mitigates Fermi level pinning. Thus, a larger degree of downward band bending on the absorber surface is realized, contributing to the efficient charge carrier transport. By fine-tuning the B-modification process, a competitive and stabilized power conversion efficiency (PCE) of 13.35% have been attained, alongside an extraordinary V_OC of 0.58 V, which highlights the great potential of modifying the HEI with non-metallic elements for future research.