In organic solar cells (OSCs), improving the properties at the interface of the bulk heterojunction (BHJ) photoactive layer and the buffer layer is desired, but achieving a high-quality interface between these two layers is inevitably challenging. Herein, a novel (PC61BM)-doped zinc oxide, that is, a (PC61BM-ZnO)DEZ hybrid thin film, is proposed for application as a cathode buffer layer (CBL) for OSCs based on both fullerene-based acceptors and nonfullerene acceptors. These thin films require low annealing temperatures and can be deposited via a one-step solution-processable method using a hybrid precursor composed of PC61BM and diethylzinc solution (DEZ). The study reveals that the performance of devices with (PC61BM-ZnO)DEZ hybrid thin films as a CBL exceeds that of devices with thin films of conventional ZnO as a CBL. Impedance analysis of the fabricated OSCs suggests improved charge collection efficiency in the devices with (PC61BM-ZnO)DEZ thin film. Optical, electrical, morphological, and compositional characterizations of thin films used as CBLs confirm the presence of a PC61BM-rich phase with traces of d-C61 (fullerene dimer) at the surface of the hybrid (PC61BM-ZnO)DEZ thin film. These phases help in tuning the interfacial properties by ensuring better coupling between the BHJ photoactive layer and the CBL. © 2022 Wiley-VCH GmbH.