Mechanism of Defect Passivation in Sb₂Se₃ Solar Cells via Buried Selenium Seed Layer

Quasi‐1D antimony selenide (Sb 2 Se 3 ) is known for its stable phase structure and excellent light absorption coefficient, making it a promising material for high‐efficiency light harvesting. However, the (Sb 4 Se 6 ) n ribbons align horizontally, increasing defect interference and limiting vertical carrier transport. Herein, a novel strategy of burying selenium (Se) seed layers to reduce lattice mismatch at the heterojunction interface, promote crystal orientation, mitigate deep donor defects, increase P‐type carrier concentration, and purify the PN junction, is proposed. Admittance spectroscopy reveals that Sb 2 Se 3 solar cells with Se seed layers have higher activation energies for defect states and significantly lower defect densities (1.2 × 10 14 , 2.7 × 10 14 , and 1.3 × 10 15 cm −3 for D1, D2, and D3) compared to an order of magnitude higher densities in Sb 2 Se 3 solar cells without a Se seed layer. First‐principles calculations support these findings, showing that Se seed layers create a Se‐rich environment, reducing selenium vacancies ( V Se ), antimony on selenium sites ( Sb Se ), and interface defects. This dual passivation mechanism suppresses defect formation and activation, increasing carrier concentration and open‐circuit voltage ( V OC ). Ultimately, employing this novel method, a V OC of 498.3 mV and an efficiency of 8.42%, the highest performance reported for Sb 2 Se 3 solar cells prepared via vapor transport deposition (VTD), are achieved.