Organic solar cells (OSCs) have attracted attention due to their lightweight nature, flexibility, and facile preparation using solution-based methods. Their efficiency has been further elevated by the rapid advancement of nonfullerene materials, achieving individual cell efficiencies that surpass 19%. Hence, the stability of nonfullerene solar cell production must be scrutinized. The stability of the cathode interface layer significantly impacts the overall stability of OSC devices. PFN-Br, a commonly employed cathode interface material, is susceptible to degradation due to its sensitivity to environmental humidity, consequently compromising the device stability. In this study, we introduce fluorescent dye molecules, rhodamine 101, as cathode interface layers in OSCs to establish device stability and assess their universality. A comparative investigation of rhodamine 101 and PFN-Br devices demonstrates the former’s distinct advantages in terms of thermal stability, photostability, and storage stability even without encapsulation, particularly in an inert environment. By employing the Kelvin probe, we compare the work function of different cathode interface films and reveal that the work function of the rhodamine 101 interface material remains relatively unaffected by environmental factors. As a consequence, the device performance stability is significantly enhanced. The application of such fluorescent dye molecules extends the scope of cathode interface layers, amplifies device stability, and propels industrialization.