Revealing critical roles of active layer morphology for suppressing interface-related degradation of organic solar cells under illumination

Abstract

Identification of degradation pathways is crucial for enhancing stability of organic solar cells (OSCs) but is challenging due to complexity in functional layers and their interfaces. This study employs planar heterojunction (PHJ) and bulk heterojunction (BHJ) devices with fine-turned active layer microstructure combined with various representative hole transport layers (HTLs) to identify device degradation pathways and mitigation strategies. Based on PHJ devices, we reveal interfacial changes between HTLs and polymer donors under illumination as the dominant degradation pathway. Crucially, polymer donors with more face-on orientation, higher crystallinity and larger aggregation size can effectively mitigate interface-related degradation. Accordingly, BHJ devices based on four material systems showed that active layers with higher crystallinity and larger domain size result in significantly enhanced device photostability across all the investigated HTLs. These findings provide guidelines for morphology engineering towards photostability enhancement of OSCs.