Key molecular perspectives for high stability in organic photovoltaics

Organic photovoltaics (OPVs) have rapidly improved in efficiency, with single-junction cells now exceeding 18% efficiency. These improvements have been driven by the adoption of new non-fullerene acceptors and the fine tuning of their molecular structures. Although OPVs are highly efficient, they often show extremely poor operational stability, primarily owing to the complex interplay between the morphological instability of the blended bulk heterojunction photoactive layers and the intrinsically poor photostability of the organic semiconductor materials themselves. To realize commercialization, it is vital to understand the degradation mechanisms of these organic materials to improve their stability. Efficiency increases have, in part, been driven by the rational molecular design of materials. In this Perspective, we examine how a similar bottom-up molecular design can be applied to OPV stability. Specifically, we highlight key molecular design parameters and demonstrate how each parameter impacts different degradation pathways. Looking forward, we propose that fundamental understanding of the molecular origin of OPV stability is a key research theme for next-generation OPVs. Additionally, we discuss the tools required, across length scales, to implement these design rules, particularly the use of in situ Raman spectroscopy as a critical bridge linking the molecular scale to the nanoscale and beyond. Organic photovoltaics show promising efficiencies and attractive properties, but their commercialization is limited by their poor operational stabilities. In this Perspective, the authors examine how bottom-up molecular design can be applied to organic semiconducting materials to achieve improved device stability.