Li Xian'e, Zhang Qilun, Yu Jianwei, Xu Ye, Zhang Rui, Wang Chuanfei, Zhang Huotian, Fabiano Simone, Liu Xianjie, Hou Jianhui, Gao Feng, Fahlman Mats
Laboratory of Organic Electronics, Department of Science and Technology (ITN), Linköping University, Norrköping, SE-60174, Sweden.
Biomolecular and Organic Electronics, Department of Physics, Chemistry and Biology (IFM), Linköping University, Linköping, SE-58183, Sweden.
Nat Commun. 2022 Apr 19;13(1):2046. doi: 10.1038/s41467-022-29702-w.
Energy level alignment (ELA) at donor (D) -acceptor (A) heterojunctions is essential for understanding the charge generation and recombination process in organic photovoltaic devices. However, the ELA at the D-A interfaces is largely underdetermined, resulting in debates on the fundamental operating mechanisms of high-efficiency non-fullerene organic solar cells. Here, we systematically investigate ELA and its depth-dependent variation of a range of donor/non-fullerene-acceptor interfaces by fabricating and characterizing D-A quasi bilayers and planar bilayers. In contrast to previous assumptions, we observe significant vacuum level (VL) shifts existing at the D-A interfaces, which are demonstrated to be abrupt, extending over only 1-2 layers at the heterojunctions, and are attributed to interface dipoles induced by D-A electrostatic potential differences. The VL shifts result in reduced interfacial energetic offsets and increased charge transfer (CT) state energies which reconcile the conflicting observations of large energy level offsets inferred from neat films and large CT energies of donor - non-fullerene-acceptor systems.
供体（D）-受体（A）异质结处的能级排列（ELA）对于理解有机光伏器件中的电荷产生和复合过程至关重要。然而，D-A界面处的ELA在很大程度上尚未确定，这导致了关于高效非富勒烯有机太阳能电池基本运行机制的争论。在此，我们通过制备和表征D-A准双层和平面双层，系统地研究了一系列供体/非富勒烯受体界面的ELA及其随深度的变化。与先前的假设相反，我们观察到D-A界面处存在显著的真空能级（VL）位移，这些位移被证明是突然的，在异质结处仅延伸1-2层，并且归因于D-A静电势差引起的界面偶极子。VL位移导致界面能量偏移减小和电荷转移（CT）态能量增加，这调和了从纯薄膜推断出的大能级偏移和供体-非富勒烯-受体系统的大CT能量之间相互矛盾的观察结果。
