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

Quasi-1D antimony selenide (Sb₂Se₃) is known for its stable phase structure and excellent light absorption coefficient, making it a promising material for high-efficiency light harvesting. However, the (Sb₄Se₆)_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 Sb₂Se₃ solar cells with Se seed layers have higher activation energies for defect states and significantly lower defect densities (1.2 × 10¹⁴, 2.7 × 10¹⁴, and 1.3 × 10¹⁵ cm⁻³ for D1, D2, and D3) compared to an order of magnitude higher densities in Sb₂Se₃ 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 Sb₂Se₃ solar cells prepared via vapor transport deposition (VTD), are achieved.