Suppressed Degradation Process of Green-Solvent Based Organic Solar Cells Through ZnO Modification With Sulfhydryl Derivatives

Abstract

The interface of organic solar cells plays a crucial role in device performance and stability. Several investigations demonstrated that the interface will affect the morphology and microstructure of the active layer, which is important for device performance. Here, several mercaptan derivatives are explored in green-solvent based organic solar cells (PBDB-TF-T1: BTP-4F-12) as effective stabilization modifiers on ZnO. Operando grazing-incidence wide/small-angle X-ray scattering (GIWAXS/GISAXS) provides a deep understanding of the degradation process during operation. The degradation process is driven by a compression of the molecule stacking as well as a decrease in the donor crystallinity, besides the known decomposition of the acceptor at the interface. Solar cell degradation comprises three stages, where an unexpected component from the acceptor appears in the second stage, simultaneously with a shapely shrinking micro-structure. Furthermore, the interface modifier pentaerythritol tetrakis(3-mercapto-propionate) (PETMP) stabilizes the crystallinity of the donor as well as suppresses the decomposition of the acceptor, thus improving the device stability. The modification effect is caused by the interaction between Zn and S from the sulfhydryl groups of the mercaptan derivatives. Thus, studies of changes in the active layer morphology extend the knowledge from ex situ characterizations, broadening the understanding of the degradation mechanisms.