Departamento de Física Aplicada, Universidad Politécnica de Cartagena, Cartagena, 30202, Spain.
Departamento de Electrónica, Universidad Politécnica de Cartagena, Cartagena, 30202, Spain.
Sci Rep. 2017 Jun 27;7(1):4297. doi: 10.1038/s41598-017-04621-9.
Charge separation is a critical process for achieving high efficiencies in organic photovoltaic cells. The initial tightly bound excitonic electron-hole pair has to dissociate fast enough in order to avoid photocurrent generation and thus power conversion efficiency loss via geminate recombination. Such process takes place assisted by transitional states that lie between the initial exciton and the free charge state. Due to spin conservation rules these intermediate charge transfer states typically have singlet character. Here we propose a donor-acceptor model for a generic organic photovoltaic cell in which the process of charge separation is modulated by a magnetic field which tunes the energy levels. The impact of a magnetic field is to intensify the generation of charge transfer states with triplet character via inter-system crossing. As the ground state of the system has singlet character, triplet states are recombination-protected, thus leading to a higher probability of successful charge separation. Using the open quantum systems formalism we demonstrate that the population of triplet charge transfer states grows in the presence of a magnetic field, and discuss the impact on carrier population and hence photocurrent, highlighting its potential as a tool for research on charge transfer kinetics in this complex systems.
电荷分离是实现有机光伏电池高效率的关键过程。初始紧密结合的激子电子-空穴对必须足够快地解离，以避免通过复合而产生光电流，从而导致功率转换效率损失。这个过程在初始激子和自由电荷状态之间的过渡态的辅助下发生。由于自旋守恒规则，这些中间电荷转移态通常具有单线态特征。在这里，我们提出了一个通用有机光伏电池的施主-受主模型，其中电荷分离过程通过调节能级的磁场来调制。磁场的影响是通过系间窜越来增强具有三重态特征的电荷转移态的生成。由于系统的基态具有单线态特征，三重态是复合保护的，因此导致成功电荷分离的概率更高。我们使用开放量子系统形式主义证明了在磁场存在下，三重态电荷转移态的种群增加，并讨论了其对载流子种群的影响，从而对光电流产生影响，突出了它作为研究这一复杂系统中电荷转移动力学的工具的潜力。
