Unveiling fixed charge field-effect passivation at the CdS/Sb2Se3 interface for minimized voltage loss

Field-effect passivation using fixed-charge dielectric layers, such as Ta2O5, can effectively suppress interfacial recombination between the electron transport layer and absorber in antimony selenide (Sb2Se3) thin-film solar cells. However, the underlying mechanisms and general design guidelines remain poorly understood. Herein, we perform finite-element simulations to systematically elucidate the fixed charge field-effect passivation at the CdS/Sb2Se3 interface upon Ta2O5 insertion, considering interface trap density, fixed charge density, and Ta2O5 thickness. Our results reveal that the positive-fixed charges of the Ta2O5 layer repel photogenerated holes back into the absorber, which significantly reduces the interfacial hole concentration and suppresses the recombination rate for minimized voltage loss. A power conversion efficiency of 14.49% is achieved for the device incorporating a Ta2O5 passivation layer, compared with 12.9% for the control one. Furthermore, the effectiveness of the field-effect passivation in suppressing trap-assisted recombination depends primarily on charge density, although its beneficial effect saturates beyond a certain value. Also, an optimal Ta2O5 thickness is notable, to balance the enhanced field-effect passivation and the increased series resistance arising from the low-conductivity Ta2O5 layer. Our findings establish a comprehensive physical model and provide universal design guidelines for field-effect passivation in fabricating high-performance Sb2Se3 and other chalcogenide solar cells.