Investigating the Role of Cathode Buffer Layers Based on Zinc Oxide with Surface-Rich Graded Fullerene Isomers in Tuning the Interfacial Properties of Organic Solar Cells

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.

Automated summary

A hybrid thin film, (PC61BM-ZnO)(DEZ), is proposed as a cathode buffer layer for organic solar cells. The thin film can be deposited via a one-step solution-processable method and requires low annealing temperatures. Compared to conventional ZnO thin films, the devices with (PC61BM-ZnO)(DEZ) as a buffer layer show improved performance.