Atomic-Scale Defect Reconfiguration via Thermally Induced Structural Ordering for High-Efficiency Sb₂Se₃ Solar Cells

The photovoltaic performance of antimony triselenide (Sb₂Se₃) thin-film solar cells is fundamentally limited by deep-level defects originating from structural disorder, which severely limit carrier lifetimes. Herein, we propose a thermodynamically driven disorder-to-order transition pathway in Sb₂Se₃ thin films, enabled by a solution-processable MgCl₂ treatment that facilitates atomic-scale defect passivation across the surface, bulk, and bottom regions. First-principles calculations reveal that Mg²⁺ and Cl^- ions preferentially occupy Sb and Se vacancies, respectively, thereby modulating vacancy concentrations and blocking atomic migration pathways, which effectively reduces the concentration of pre-existing antisite defects. In parallel, the in situ formation of metastable intermediates (e.g., MgSe^-, MgSe₂^-, and Se³⁷Cl^-) acts as a kinetic accelerator for microstructural reconstruction, driving the transformation of disordered nanograins into highly oriented, micron-scale single crystals. This synergistic ionic and structural reconfiguration leads to a 10-fold reduction in trap density and extends photocarrier lifetimes from 0.08-2.6 to 2.7-17 μs, substantially mitigating nonradiative recombination. Consequently, vapor-transport-deposited Sb₂Se₃ solar cells achieve a certified efficiency of 9.31%, establishing a benchmark. This work provides a mechanistic framework that integrates ionic defect chemistry with lattice ordering, offering a generalizable pathway for enabling low-dimensional photovoltaics.