Additive strategy is considered to be an effective way to achieve high-efficiency organic solar cells (OSCs). However, for heat-sensitive material systems, such as D18 and its derivatives, solvent additives with high-boiling points that need to be fully removed by high-temperature annealing often fail to optimize the device performance. Herein, based on the D18-Cl:Y6-based device, we chose the volatile solvent tetrahydrofuran (THF) as the solvent additive, which can achieve effects similar to high-boiling-point additives without thermal annealing. The addition of THF effectively improves the charge transport and film morphology of the active layer, the fill factor (FF) of the device is increased from 74.20 to 75.91%, and the photoelectric conversion efficiency (PCE) is increased from 16.85 to 17.70%. Further research compared the effects of THF and its derivatives and structural analogs on the device performance and explored the effect of THF on the device performance of different material systems, and the results show that volatile solvent additives have certain generality in improving film morphology. Our results indicate that the selection of volatile solvents as solvent additives is a promising strategy that can effectively improve the performance of OSCs.