Thermally Stable Organic Solar Cells with a Self-Assembled Passivation Layer: Insight into the Interfacial Degradation of Non-Fullerene Acceptors
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Despite recent progress in small molecule nonfullerene acceptor (SM-NFA)-based organic solar cells (OSCs), their poor thermal stability hinders their commercial applications. While the morphological instability of the bulk heterojunction (BHJ) is known, interfacial deterioration between SM-NFAs and the reactive species-containing interfacial layer is equally crucial. We identified chemical degradation of SM-NFA on a ZnO surface under thermal stress using OrbiSIMS. Through a systematic examination of the relationship between the thermal transition temperature (Tg) of SM-NFA and the thermal-induced degradation at the interface, rapid interfacial SM-NFA degradation was observed as their Tg values decreased. To mitigate this, a self-assembly method with 5-methyl-1H-benzotriazole (M-BT) was introduced to passivate the ZnO surface. OSCs with M-BT retained over 85% of their initial power conversion efficiency (PCE) after 1000 h at 85℃, while the control device exhibited a short T85 within 20 h.