Unveiling Energy Loss Mechanisms to Empower Ternary Organic Solar Cells with over 20% Efficiency: A Systematic Oligomeric Approach
Hao Xia, Caifa You, Jiehao Fu, Dou Luo, Ruijie Ma, Heng Liu, Yongwen Lang, Xinhui Lu, Weiguo Zhu, Gang Li
Abstract
Abstract In organic solar cells (OSCs), the ternary strategy is a mainstream approach to obtaining highly efficient OSCs. A deeper understanding of working mechanisms and the material selection criteria for boosting open‐circuit voltage ( V OC ) is essential for further OSC breakthrough. Through a modular design principle, a series of oligomeric donors – 5BDD, 5BDD‐F, 5BDT‐F, and 5BDT‐Cl – with similar molecular configurations but varying HOMO levels is systematically designed. These findings reveal that the HOMO levels of these oligomers have a negligible impact on the V OC of the ternary OSCs. Instead, their excellent compatibility with acceptors played a pivotal role in enhancing V OC . The oligomers effectively suppressed excessive acceptor aggregation and achieved Aggregation‐Caused Quenching Suppression (ACQS), strengthening the external electroluminescence quantum efficiency (EQE EL ) and reducing non‐radiative recombination energy losses. Simultaneously, oligomers fine‐tuned and optimized the morphology of the blend films, leading to a higher fill factor (FF) and improved performance. Notably, the 5BDT‐F‐ and 5BDT‐Cl‐based ternary OSCs achieved impressive power conversion efficiencies (PCEs) of 19.8% and 20.1% (certified 19.76%), with FFs of 80.9% and 80.7%, respectively. This work elucidates the unusual role of the third component energy levels on the V OC in ternary OSCs and offers valuable guidance for future OSC design.