The efficient generation and transportation of charge carriers are the major factors that influence the performance of thin film organic solar cells (TFOSC). In this study, we have successfully synthesized and employed a trimetallic nanocomposite (Ag:Zn:Ni) in the preparation of TFOSCs in order to address these challenges. The nanocomposites were dispersed in the solution phase of the photo-active layer of the solar cells. The effects of the nanocomposites were observed on the power conversion efficiency of the devices due to local surface plasmon resonance. In this study, trimetallic nanoparticles were used for the first time in the photoactive medium of inverted TFOSCs that survived for more than 90 days in an ambient environment. The synthesis of the nanocomposite, device preparation method, and characterization of the product were investigated in terms of the changes in the optical, electrical, and morphological properties.