高效单重态裂分有机光伏器件中三重态激子动力学过程的调控

The implementation of singlet fission (SF) in organic photovoltaic (OPV) devices is a promising way to surpass the Shockley-Queisser limit of conventional single-junction solar cells owing to the two triplet excitons generation with one photon absorption. However, the efficiency of the SF-based OPVs is relatively low due to the imbalance in exciton dynamic processes. Therefore, it is necessary to manipulate and balance the dynamic processes of triplet exciton including exciton generation, diffusion and separation to achieve high performance devices. In this program, we will investigate the photo active layer composed of SF-donor/acceptor bulk heterojunction blend films whose nano-scale morphology can be effectively controlled under various external fields. The morphology at multiple length scale will be quantitatively analyzed by high resolution microscopy and Synchrotron based spectroscopy (GIXD, GISAXS, GIWAXS). Together with high resolution spatio-temporal resolved absorption and fluorescence micro-spectroscopy, the generation, diffusion and separation processes of triplet exciton in blend films with specific morphology will be investigated. Finally, a correlation between the film morphology and the dynamic processes of triplet exciton can be quantitatively established, which in-turn provides principle guidance for manipulating and balancing the dynamic process by the morphology control. This work will be of great value not only for achieving high performance SF-based OPV devices, but also for the exploration of singlet fission in other applications.

单重态裂分有机光伏器件每吸收一个光子可产生两个三重态激子，理论上可获得超过肖克莱-奎瑟尔极限的能量转换效率，但实际器件效率并不高。深入理解并调控三重态激子产生、扩散、分离三个动力学过程使其达到平衡，是提高单重态裂分有机光伏器件性能的有效途径。本项目通过外场作用调控单重态裂分给体材料与适当受体材料组成的体异质结活性层薄膜微纳结构，利用高分辨率显微系统与同步辐射X射线散射/衍射等技术定量获取薄膜的相分离尺寸、微区结晶度、分子堆积方式等结构信息，并采用时间分辨显微光谱学技术在超快时间尺度上解析其三重态激子动力学过程，建立微纳结构与动力学过程的内在关联机制，获取各个动力学过程达到最佳平衡时所对应的活性层薄膜微纳结构和外场控制条件，最终获得高效单重态裂分有机光伏原型器件。本研究不仅在提高单重态裂分有机光伏器件性能方面具有理论及应用价值，对于单重态裂分效应在其它领域的开发利用也具有重要参考意义。

深入理解并调控三重态激子产生、扩散、分离三个动力学过程使其达到平衡，是提高单重态裂分有机光伏器件性能的有效途径。本项目根据不同有机光伏材料的吸收谱、光致荧光谱、溶解度等相关信息选取了多种单重态裂分给体材料与受体材料，采用真空蒸镀，旋涂等制备工艺，将单重态裂分材料制备成单重态裂分有机半导体双层/体异质结结构薄膜。通过常规的形貌表征手段，如AFM、SEM等，观察薄膜的微纳结构；利用高分辨率显微系统与同步辐射X射线散射/衍射等技术定量获取薄膜的相分离尺寸、微区结晶度、分子堆积方式等结构信息；利用时间分辨显微光谱学技术在超快时间尺度上解析其三重态激子动力学过程，建立微纳结构与动力学过程的内在关联机制，超快荧光显微技术能够同时在时间和空间的尺度上得到材料的发光性质，因此，可以进一步得到共混材料中的激子扩散、解离等光物理现象，最终我们通过多种优化策略改善了体异质结内分子堆积等形貌特性，制备出了更高效率的有机光伏原型器件。本项目的成果为单重态裂分有机光伏器件的制备提供了全新的角度和理论依据，对有机太阳能能电池未来的发展具有重要意义。