Spontaneously spreading (SS) film process with water substrates in the air (inert free atmosphere) has recently emerged as an effective technique for the fabrication of large-area organic solar cells (OSCs), however, there are limited studies on the process until now. Herein, we carried out an in-depth study on the influence of varying the temperature of the water substrate during the SS process on the quality of the film and performance of two test-bed OSC devices (PM6:ITIC-4F and PM6:Y7). By accounting for the changes in the kinetics and thermodynamics of the evaporation and dissolution of the solvent in water, we observed a striking water temperature dependence of the morphology and OSC performance. Via careful device optimization with the varying water temperatures, we achieved high power conversion efficiencies (PCEs) of 11.13% and 13.83% for PM6:ITIC-4F-and PM6:Y7-based SS-OSCs processed at 25 °C water temperature, respectively. The 13.83% PCE is the hitherto the highest reported value of the air-processed SS-OSCs. The strategy reported herein with which the quality of films can be controlled by simple modulation of the water temperature can promote the utilization of the SS process in the fabrication of scalable devices of various organic semiconductors.