<p>Antimony selenide (Sb₂Se₃) has emerged as a promising thin-film photovoltaic absorber due to its ideal bandgap (1.1–1.3 eV), high absorption coefficient (&gt;10⁵ cm⁻¹) and environmentally benign composition. However, Sb₂Se₃ solar cells (SSCs) often suffer from large open-circuit voltage losses owing to the weak built-in fields and severe non-radiative recombination at the interfaces and within the absorber layer. Here we demonstrate a composition-driven strategy for controlling carrier polarity that we used to form an n-type/p-type homojunction within the Sb₂Se₃ absorber layer. By precisely tuning the chemical potentials of Se and Sb, we are able to manipulate the conductivity type and achieve carrier densities exceeding 10¹⁴ cm⁻³ for the n- and p-type states. With this materials design, we demonstrate that incorporating the p–n homojunction into a planar SSC simultaneously enhances the built-in electric field and passivates deep-level defects. These synergistic effects promote carrier separation, reduce non-radiative recombination and accelerate carrier extraction. As a result, the internal-homojunction-enhanced SSC delivers a power conversion efficiency of 10.15% for thermally evaporated Sb₂Se₃ devices and an ultralow open-circuit voltage deficit of 0.459 V. This study proposes a proof-of-concept device structure for SSCs that opens a new pathway for improving device efficiency.</p>