Charge Generation Mechanism of Polymer Photovoltaics

Abstract

<p>Polymer photovoltaics have achieved considerable development in recent years, and the latest Y-series non-fullerene acceptors represented by Y6 have boosted the power conversion efficiencies to nearly 20%, while some of their working mechanisms have not yet been fully understood. This paper reviews the research reports on the charge generation mechanism of polymer photovoltaic systems based on fullerene acceptors and non-fullerene acceptors in recent years, and compares the similarities and differences of the working mechanisms of the two systems and the possible reasons for the high performance of the Y series. Generally, the polymer donor-fullerene acceptor systems can achieve ultrafast charge separation, but suffers from large energy loss, which limits the improvement of their performance; the polymer donor-non-fullerene acceptor systems show greatly reduced energy loss, but their charge generation process is relatively slow, and in some cases the assistance of thermal energy is required. Y series acceptors have unique molecular packing way and charge generation kinetics which both contribute to their remarkable performance, while the specific mechanism of charge generation is still controversial. Also, possible methods and prospects for further reducing energy loss and improving device performance are proposed. It is clear that nonradiative recombination losses must be further reduced to achieve higher device performances, possibly by improving the photoluminescence quantum efficiency and fine-tuning the kinetics of the interconversion between excited state and charge transfer state. Finally, continuous efforts on improving the long term stability of polymer photovoltaic devices are still needed to promote their commercialization in the future.<br></p>

聚合物有机光伏近年来已经获得长足的发展，最新的研究报道以Y6为代表的Y系列非富勒烯受体体系取得了接近20%的能量转换效率，然而其电荷产生的具体机制尚存在争议. 本文回顾了近年来对基于富勒烯受体和非富勒烯受体的聚合物有机光伏体系的电荷产生机理的研究报道，介绍了2种体系工作机理的异同，指出富勒烯体系虽然可以实现超快的电荷分离，却普遍存在较大的能量损失；非富勒烯体系大幅降低了器件的能量损失，但其电荷产生过程相对较慢，并且在一些情况下需要热能的辅助来实现. 本文分析了Y系列体系实现高性能的可能原因，分析表明其具有的独特的分子堆积方式和电荷产生动力学均对其优异的性能有所贡献，并提出了进一步降低能量损失和提高器件性能的可能方法与展望.