Enhance Photo-Stability of Up-Scalable Organic Solar Cells: Suppressing Radical Generation in Polymer Donors.

The power conversion efficiency (PCE) of single-junction organic solar cells (OSCs) has been promoted above 20%. Device up-scaling draws more and more research attentions. Besides the high PCE for devices with up-scalable fabrication methods and conditions, achieving high stability simultaneously is essential for pushing industrialization of this technology. Here, the stability of the state-of-the-art OSCs blade-coated in air with non-halogenated solvents in a wide thickness range is thoroughly investigated. The losses in short-circuit current density under photo-thermal stress strongly depend on processing conditions. Devices with less crystalline phases in unit thickness show faster generation of trap states and hence strongly reduced charge collection efficiency. Through in-depth photo-chemical, photo-physical, and morphological characterizations during ageing, faster generation of radicals in PM6 for active layers with more amorphous structures is identified as the cause for device degradation. Increasing the crystallinity of active layer films for suppressing radical generation in polymer donors is critical to enhance the photo-thermal stability of devices processed in air with a wide thickness range.