Enhancing photostability and power conversion efficiency of organic solar cells by a "sunscreen" ternary strategy

The field has witnessed the rapid growth in the power conversion efficiency (PCE) of organic solar cells (OSCs) over the past decade, reaching the threshold for practical commercialization. However, a major issue remains that OSC lifetimes are seriously limited by the ultraviolet (UV)-induced photodegradation. Here, inspired by the superior photostability of car paint under sunlight and ambient air, a "sunscreen" molecule, 2-(2-hydroxy-5-tert-octylphenyl)benzotriazole (UV329), is used to construct the PM6:Y6 ternary device. The addition of UV329 mainly enhances the ordered stacking of PM6 and increases the light utilization of blend films with the improved crystallization and appropriate phase separation. Accordingly, the ternary device exhibits stronger light response and obviously higher and more balanced carrier mobilities, contributing to higher short-circuit current density, fill factor and PCE. Similar PCE boost is also verified in PM6:BTP-eC9 and PM6:L8-BO systems. The photodegradation of PM6 dominates the photo-degradation process of PM6:Y6 systems, while the UV329 can effectively suppress such degradation, and thus the ternary device can retain nearly 90% of the initial PCE under continuous illumination for 120 min. Moreover, ternary devices also preserve better thermal stability and shelf-life with the enhanced PCE. This work provides a simple yet effective strategy for simultaneously improving PCE and photostability of OSCs.