三元非富勒烯太阳能电池的电荷复合和开路电压损失机制研究

Recombination losses are critically important for photovoltaic device characteristics and ultimate power conversion efficiencies (PCE) of organic solar cells. Charge transport and morphological properties play a significant role for the recombination processes in the organic photoactive layer. In recently years, there have has been tremendous progress received by our Chinese research communities in the materials design and device engineering for high performance organic ternary solar cells. While the utilization of ternary bulk heterojunction blends to boost the photon harvesting via the increase of absorbed carriers may be traded off by a reduction in the open-circuit voltage. So far, our fundamental knowledge on charge recombination relevant to the losses in photocarriers and open circuit voltage in ternary solar cells is still far from clearance. To this end, in this proposal, based the established understandings on binary devices, we will focus on investigating how charge transport and intermolecular packing affect non-geminate recombination, charge transfer states and non-radiation voltage losses in ternary solar cells that are modulated through the incorporated guest molecules. We aim to attain in-depth insights into the correlations between transport properties-morphology-recombination-performance in these emerging devices, from which suitable models describing the open-circuit voltage in ternary solar cells are to be derived. The fundamental advances gained from the proposed studies are beneficial for simultaneously enhancing the short-circuit current and open-circuit voltage, and eventually the PCE of non-fullerene ternary organic solar cells.

电荷复合是影响有机太阳能电池工作参数和导致其效率损失的重要因素。有机半导体活性层的电荷复合过程与载流子迁移率及其形貌密切相关。近年来，我国在三元共混有机太阳能电池的材料设计和效率优化方面取得了显著成绩。然而，三元共混的方式在提升器件对太阳光的利用率和载流子浓度的同时，有可能引起其开路电压的下降。目前，本领域对这一类新型电池结构中的电荷复合和开路电压损失机理尚不十分清楚。因此，基于对二元有机太阳能器件物理的理解，本申请课题拟针对三元有机非富勒烯太阳能电池，通过客体分子调控共混本体异质结的载流子迁移率和形貌等特性，在此基础上研究载流子输运性质、分子排列和能级对三元电池的电荷复合、电荷转移态以及非辐射损失的影响规律，探索电学性质-形貌-电荷复合-工作参数之间的科学关系，完善三元电池开路电压损失的理论模型，为同时改善三元非富勒烯有机太阳能电池的短路电流和开路电压以及最终的转换效率提供参考依据。

三元共混是调控有机体异质结形貌和光伏器件性能的重要方法，理解和降低器件的电压损失提升三元有机太阳能电池工作性能的关键。本项目针对非富勒烯有机太阳能电池，研究了光活性层的材料和物理特性对器件开路电压损失的影响机制，从载流子输运的角度提出了迁移率的平衡性对降低器件的非辐射电压损失的重要性；从分子兼容性的角度揭示出非富勒烯受体作为组分调控分子与主体分子之间的兼容性对三元电池的开路电压和载流子复合的影响规律；基于系列能级渐变的有机光伏材料体系，揭示出有机太阳能电池的开路电压与填充因子之间的相互制约关系；深入探索了活性层分子的堆积密度对器件光伏性能的影响机制，提出了基于增加分子堆积密度改善器件填充因子和开路电压的新思路；此外，项目负责人提出了在受体富集层内分散给体组分的新结构概念，有效降低了三元电池的载流子复合损失，实现了器件光伏性能的提升。上述研究成果丰富了调控有机太阳能电池开路电压和工作特性的实验方法，丰富了有机太阳能电池器件物理相关知识并加深了机理理解水平。在本项目支持下，负责人以通讯作者身份在Joule、Adv. Mater.、Nano Energy等国际学术刊物上发表研究论文18篇，培养了1名博士后和9名研究生, 其中多名学生获得奖学金。