Xie Xiaoyu, Zhang Chunfeng, Ma Haibo
School of Chemistry and Chemical Engineering, Nanjing University, Nanjing 210023, China.
National Laboratory of Solid State Microstructures, School of Physics, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093, China.
J Chem Phys. 2020 Aug 7;153(5):054705. doi: 10.1063/5.0013466.
In recently developed non-fullerene acceptor (NFA) based organic solar cells (OSCs), both the donor and acceptor parts can be excited by absorbing light photons. Therefore, both the electron transfer and hole transfer channels could occur at the donor/acceptor interface for generating free charge carriers in NFA based OSCs. However, in many molecular and DNA systems, recent studies revealed that the high charge transfer (CT) efficiency cannot be reasonably explained by a CT model with only highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) of donor and acceptor molecules. In this work, taking an example of a full-polymer blend consisting of benzodithiophene-alt-benzotriazole copolymers (J51) as donor and naphthalene diimide-bithiophene (N2200) as acceptor, in which the ultrafast hole transfer has been recently reported, we investigate its CT process and examine the different roles of various frontier molecular orbitals (FMOs). Through a joint study of quantum mechanics electronic structure calculation and nonadiabatic dynamics simulation, we find that the hole transfer between HOMOs of J51 and N2200 can hardly happen, but the hole transfer from HOMO of N2200 to HOMO - 1 of J51 is much more efficient. This points out the underlying importance of the deep hole channel in the CT process and indicates that including FMOs other than HOMOs and LUMOs is highly necessary to build a robust physical model for studying the CT process in molecular optoelectronic materials.
在最近开发的基于非富勒烯受体（NFA）的有机太阳能电池（OSC）中，供体和受体部分都可以通过吸收光光子而被激发。因此，在基于NFA的OSC中，电子转移和空穴转移通道都可能在供体/受体界面处发生，以产生自由电荷载流子。然而，在许多分子和DNA系统中，最近的研究表明，仅用供体和受体分子的最高占据分子轨道（HOMO）和最低未占据分子轨道（LUMO）来解释高电荷转移（CT）效率是不合理的。在这项工作中，以由苯并二噻吩-alt-苯并三唑共聚物（J51）作为供体和萘二酰亚胺-联噻吩（N2200）作为受体组成的全聚合物共混物为例，其中最近报道了超快空穴转移，我们研究了其CT过程，并考察了各种前沿分子轨道（FMO）的不同作用。通过量子力学电子结构计算和非绝热动力学模拟的联合研究，我们发现J51和N2200的HOMO之间的空穴转移很难发生，但从N2200的HOMO到J51的HOMO - 1的空穴转移效率要高得多。这指出了深空穴通道在CT过程中的潜在重要性，并表明除了HOMO和LUMO之外，纳入其他FMO对于建立一个强大的物理模型来研究分子光电子材料中的CT过程是非常必要的。
