Fused-ring electron acceptor (FREA) based ternary organic solar cells (OSCs) have made significant progress and attracted considerable attention due to their simple device architecture and broad absorption range in devices. There are three key parameters that need to be fine-tuned in ternary OSCs including absorption, energy level and morphology in order to realize high efficiencies. Herein, a series of FREAs with diverse electron-rich cores or electron-deficient terminals are developed and rationally combined to achieve high performance ternary OSCs. The dipole moment of FREAs’ terminals has been unveiled as an important factor and its working mechanism has been thoroughly investigated by systematically studying six ternary OSCs. These ternary blends all exhibit complementary absorption and cascade energy levels, which can facilitate efficient light-harvesting and charge transfer. Additionally, the morphological effects on ternary OSCs are eliminated through comparative studies while demonstrating distinctively different performance. The preliminary results show that compatible dipole moment between two FREAs is critical in ternary blends. Specifically, the performance of the ternary system with two FREAs having quite different dipole moment terminals is worse compared to that with similar terminal dipole moments. The pair with larger difference in the dipole moment will also negatively impact device performance. This interesting phenomenon is likely due to the fact that very different dipole moments of terminals in FREAs can significantly decrease the electron mobility as well as induce unbalanced hole/electron transport. Consequently, it results in increased charge recombination and reduced charge collection efficiency. This finding demonstrates that the dipole moment of FREAs should be taken into account in designing ternary OSCs.

中文翻译：

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偶极矩在两个稠环电子受体和一个聚合物供体基三元有机太阳能电池中的作用

基于融合环电子受体（FREA）的三元有机太阳能电池（OSC）取得了重大进展，并且由于其简单的器件架构和广泛的吸收范围而引起了广泛的关注。为了实现高效率，三元OSC中需要对三个关键参数进行微调，包括吸收，能级和形态。在此，开发并合理组合了一系列具有多种富电子核心或缺电子末端的FREA，以实现高性能的三元OSC。FREAs终端的偶极矩已被揭示为一个重要因素，并且通过系统地研究六个三元OSC对它的工作机制进行了彻底研究。这些三元混合物都表现出互补的吸收能和级联能级，这可以促进高效的光收集和电荷转移。此外，通过比较研究消除了对三元OSC的形态学影响，同时表现出明显不同的性能。初步结果表明，在三元混合物中，两个FREA之间的相容偶极矩至关重要。具体地，与具有相似的末端偶极矩的两个FREA相比，具有两个FREA的三元系统的性能更差。偶极矩差异较大的线对也会对器件性能产生负面影响。这种有趣的现象很可能是由于以下事实：FREA中端子的偶极矩非常不同，会大大降低电子迁移率，并引起不平衡的空穴/电子传输。所以，它导致电荷重组增加，电荷收集效率降低。这一发现表明，在设计三元OSC时应考虑FREAs的偶极矩。