<p>This study investigates the impact of solvent annealing on the morphological, optical, and photovoltaic properties of CH₃NH₃PbI_3−xCl_x perovskite solar cells fabricated by spin coating technique. Two post-deposition treatments: solvent and thermal annealing were compared using two film thicknesses (100 and 400&#xa0;nm) to evaluate their influence on crystallinity, defect density, and energy alignment. Solvent annealing was conducted using saturated dimethylformamide vapor at room temperature. This type of annealing significantly enhances film quality, yielding smoother surfaces, finer grain uniformity, and more defined absorption edges compared to the traditional thermal annealing at 100&#xa0;°C. Optical analyses showed that solvent-annealed films exhibited an apparent bandgap widening from 1.46&#xa0;eV before the annealing to 1.86&#xa0;eV after the annealing. The effect of solvent annealing on the electronic properties showed that HOMO level was deepened, and LUMO level was raised, which could improve charge transport and reduce recombination. The solvent-annealed solar cells achieved a power conversion efficiency of 14.1%, which is higher than thermally annealed cells (12.0%) and as-deposited cells (&lt; 2%). Moreover, energy payback time was shortened to 0.095 years (~ 35 days) with solvent annealing, compared to 0.12 years with thermal processing. Subsequently, carbon emissions were also reduced by 2.7&#xa0;kg CO₂ per batch. This demonstrates that solvent annealing is considered as a low-energy, eco-friendly, and performance-enhancing strategy for scalable perovskite solar cell manufacturing, particularly suitable for low-temperature and flexible applications.</p>