High-Efficiency Small Molecule-Based Bulk-Heterojunction Solar Cells Enhanced by Additive Annealing

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• 作者：Lisheng Li ; Liangang Xiao ; Hongmei Qin ; Ke Gao ; Junbiao Peng ; Yong Cao ; Feng Liu ; Thomas P. Russell ; Xiaobin Peng
• 刊名：ACS Applied Materials & Interfaces
• 出版年：2015
• 出版时间：September 30, 2015
• 年：2015
• 卷：7
• 期：38
• 页码：21495-21502
• 全文大小：504K
• ISSN：1944-8252

文摘

Solvent additive processing is important in optimizing an active layer鈥檚 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/cm², 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.