Li Lisheng, Xiao Liangang, Qin Hongmei, Gao Ke, Peng Junbiao, Cao Yong, Liu Feng, Russell Thomas P, Peng Xiaobin
Institute of Polymer Optoelectronic Materials and Devices, State Key Laboratory of Luminescent Materials and Devices, South China University of Technology , 381 Wushan Road, Guangzhou 510640, China.
Materials Sciences Division, Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
ACS Appl Mater Interfaces. 2015 Sep 30;7(38):21495-502. doi: 10.1021/acsami.5b06691. Epub 2015 Sep 18.
Solvent additive processing is important in optimizing an active layer's morphology and thus improving the performance of organic solar cells (OSCs). In this study, we find that how 1,8-diiodooctane (DIO) additive is removed plays a critical role in determining the film morphology of the bulk heterojunction OSCs in inverted structure based on a porphyrin small molecule. Different from the cases reported for polymer-based OSCs in conventional structures, the inverted OSCs upon the quick removal of the additive either by quick vacuuming or methanol washing exhibit poorer performance. In contrast, the devices after keeping the active layers in ambient pressure with additive dwelling for about 1 h (namely, additive annealing) show an enhanced power conversion efficiency up to 7.78% with a large short circuit current of 19.25 mA/cm(2), which are among the best in small molecule-based solar cells. The detailed morphology analyses using UV-vis absorption spectroscopy, grazing incidence X-ray diffraction, resonant soft X-ray scattering, and atomic force microscopy demonstrate that the active layer shows smaller-sized phase separation but improved structure order upon additive annealing. On the contrary, the quick removal of the additive either by quick vacuuming or methanol washing keeps the active layers in an earlier stage of large scaled phase separation.
溶剂添加剂处理对于优化活性层的形态从而提高有机太阳能电池（OSC）的性能至关重要。在本研究中，我们发现1,8 - 二碘辛烷（DIO）添加剂的去除方式在决定基于卟啉小分子的倒置结构体异质结OSC的薄膜形态方面起着关键作用。与传统结构中基于聚合物的OSC的报道情况不同，通过快速抽真空或甲醇洗涤快速去除添加剂后的倒置OSC表现出较差的性能。相比之下，在常压下使活性层与添加剂共存约1小时后（即添加剂退火）的器件，功率转换效率提高到7.78%，短路电流高达19.25 mA/cm²，这在基于小分子的太阳能电池中处于最佳水平。使用紫外 - 可见吸收光谱、掠入射X射线衍射、共振软X射线散射和原子力显微镜进行的详细形态分析表明，添加剂退火后活性层的相分离尺寸更小，但结构有序性得到改善。相反，通过快速抽真空或甲醇洗涤快速去除添加剂会使活性层处于大尺度相分离的早期阶段。
