Non-equilibrium Energy Research Center, Northwestern University, Evanston, 60208, USA.
Phys Chem Chem Phys. 2012 Nov 7;14(41):14270-6. doi: 10.1039/c2cp41532a.
A simple model is constructed to describe dissociation of charge transfer excitons in bulk heterojunction solar cells, and its dependence on the physical parameters of the system. In bulk heterojunction organic photovoltaics (OPVs), exciton dissociation occurs almost exclusively at the interface between the donor and acceptor, following one-electron initial excitation from the HOMO to the LUMO levels of the donor, and charge transfer to the acceptor to make a charge-transfer exciton. After exciton breakup, and neglecting the trapping of individual carriers, the electron may undergo two processes for decay: one process involves the electron and/or hole leaving the interface, and migrating to the electrode. This is treated here as the electron moving on a set of acceptor sites. The second loss process is radiationless decay following recombination of the acceptor electron with the donor cation; this is treated by adding a relaxation term. These two processes compete with one another. We model both the exciton breakup and the subsequent electron motion. Results depend on tunneling amplitude, energetics, disorder, Coulomb barriers, and energy level matchups, particularly the so-called LUMO-LUMO offset.
我们构建了一个简单的模型来描述体异质结太阳能电池中电荷转移激子的离解，并研究了其对系统物理参数的依赖性。在体异质结有机光伏（OPV）中，激子的离解几乎完全发生在给体和受体之间的界面处，这是通过从给体的 HOMO 到 LUMO 能级的单电子初始激发以及向受体的电荷转移来实现的，从而形成电荷转移激子。在激子分裂后，忽略对单个载流子的捕获，电子可能会经历两种衰减过程：一个过程涉及电子和/或空穴离开界面并迁移到电极。这里将其处理为电子在一组受体位置上的移动。第二个损失过程是受体电子与施主阳离子复合后的无辐射衰减；通过添加弛豫项来处理这个过程。这两个过程相互竞争。我们对激子的分裂和随后的电子运动都进行了建模。结果取决于隧道振幅、能级、无序、库仑势垒和能级匹配，特别是所谓的 LUMO-LUMO 偏移。
