Long-Term Thermal Stability of Nonfullerene Organic Solar Cells via Facile Self-Assembled Interface Passivation
Sanseong Lee, Jong Sung Jin, Heehun Moon, Ju‐Hyeon Kim, Kiyoung Park, Juhui Oh, Taeyoon Ki, Soo‐Young Jang, Hongkyu Kang, Heejoo Kim, Kwanghee Lee
Abstract
Although the morphological instability of the bulk-heterojunction (BHJ) organic solar cells (OSCs) based on a small-molecule nonfullerene acceptor (SM-NFA) is regarded as an important issue for understanding thermal stability, interfacial deterioration between the chemically vulnerable SM-NFAs and an interfacial layer containing reactive species is also crucial. Herein, we identified that chemical degradation of SM-NFA on a zinc oxide (ZnO) interfacial layer under thermal stress is more critical by systematically examining three SM-NFAs that have different thermal transition temperature ( T g ) values; as T g decreased, the interfacial degradation of SM-NFAs increased. However, the introduction of a highly polar and volatile molecule, 5-methyl-1 H -benzotriazole (M-BT), into the BHJ effectively passivates the defects of the ZnO surface by forming a self-assembled layer. The optimized target device exhibited excellent long-term thermal stability that retains above 85% of the initial efficiency after 1000 h (= T 85 ) at 85 °C under a N 2 atmosphere, while a short T 85 within 20 h was obtained in the control device.