Wang Zhen, Guo Yu, Liu Xianzhao, Shu Wenchao, Han Guangchao, Ding Kan, Mukherjee Subhrangsu, Zhang Nan, Yip Hin-Lap, Yi Yuanping, Ade Harald, Chow Philip C Y
Department of Mechanical Engineering, The University of Hong Kong, Pokfulam, Hong Kong SAR, China.
CAS Key Laboratory of Organic Solids, Institute of Chemistry, Chinese Academy of Sciences, Haidian, Beijing, 100190, China.
Nat Commun. 2024 Feb 8;15(1):1212. doi: 10.1038/s41467-024-45455-0.
Polymerization of Y6-type acceptor molecules leads to bulk-heterojunction organic solar cells with both high power-conversion efficiency and device stability, but the underlying mechanism remains unclear. Here we show that the exciton recombination dynamics of polymerized Y6-type acceptors (Y6-PAs) strongly depends on the degree of aggregation. While the fast exciton recombination rate in aggregated Y6-PA competes with electron-hole separation at the donor-acceptor (D-A) interface, the much-suppressed exciton recombination rate in dispersed Y6-PA is sufficient to allow efficient free charge generation. Indeed, our experimental results and theoretical simulations reveal that Y6-PAs have larger miscibility with the donor polymer than Y6-type small molecular acceptors, leading to D-A percolation that effectively prevents the formation of Y6-PA aggregates at the interface. Besides enabling high charge generation efficiency, the interfacial D-A percolation also improves the thermodynamic stability of the blend morphology, as evident by the reduced device "burn-in" loss upon solar illumination.
Y6型受体分子的聚合可形成兼具高功率转换效率和器件稳定性的体异质结有机太阳能电池，但其潜在机制仍不清楚。在此，我们表明聚合的Y6型受体（Y6-PAs）的激子复合动力学强烈依赖于聚集程度。虽然聚集的Y6-PA中快速的激子复合速率与供体-受体（D-A）界面处的电子-空穴分离相竞争，但分散的Y6-PA中显著抑制的激子复合速率足以实现高效的自由电荷产生。事实上，我们的实验结果和理论模拟表明，Y6-PAs与供体聚合物的混溶性比Y6型小分子受体更大，导致D-A渗流，有效地防止了Y6-PA在界面处聚集。除了实现高电荷产生效率外，界面D-A渗流还提高了共混物形态的热力学稳定性，这在太阳光照下器件“老化”损失的降低中得到了体现。
