<p>Annealing is a crucial step for recrystallizing Sb₂S₃ and forming high-quality Sb₄S₆ chain-like crystals, which is essential for achieving high-efficiency photovoltaic devices. However, this process currently faces a fundamental trade-off: Although high-temperature annealing enhances crystallinity, it also introduces severe sulfur and Sb₂S₃ molecular escape, ultimately degrading device performance. To overcome this limitation, we propose a confined-space annealing (CSA) strategy that operates via a dual mechanism. Physical confinement generates a high local vapor pressure, which suppresses Sb₂S₃ re-volatilization and enables recrystallization into large-grain films under atmospheric pressure. Controlled oxygen doping preferentially fills sulfur vacancy sites, suppresses interstitial Sb_i defects, and promotes the self-assembly of Sb₂O₃ nano-belts at grain boundaries, effectively blocking leakage paths. As a result, the CSA films exhibit a 60.9% reduction in V_S defects and a 40.3% improvement in carrier collection efficiency compared to pristine films. Carbon-based devices fabricated using this approach achieve a power conversion efficiency of 7.17% (<i>V</i>_OC = 750&#xa0;mV, <i>J</i>_SC = 14.26&#xa0;mA&#xa0;cm⁻², FF = 62.7%), which is the highest reported value for Sb₂S₃ solar cells fabricated entirely in ambient atmosphere. This work not only offers a practical fabrication route under ambient conditions but also provides fundamental insights into defect passivation in chalcogenide photovoltaics.</p>