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Fluorinating Dopant-Free Small-Molecule Hole-Transport Material to Enhance the Photovoltaic Property

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journal contribution
posted on 05.02.2021, 17:33 by Yi Kai Wang, Hui Ma, Qiaoyun Chen, Quan Sun, Zhengxu Liu, Zhe Sun, Xuguang Jia, Yuanyuan Zhu, Shuai Zhang, Jing Zhang, Ningyi Yuan, Jianning Ding, Yi Zhou, Bo Song, Yongfang Li
For the stability and commercial development of the perovskite solar cells (PVK-SCs), synthesizing high-efficiency dopant-free hole-transport materials (DF-HTMs) and exploring how the DF-HTM structure affects the photovoltaic performance is inevitable. Two small-molecule DF-HTMs based on 2,2′-bithiophene as a central part (denoted by BT-MTP and DFBT-MTP) were designed and synthesized. DFBT-MTP, with two more fluorine atoms substituted on the 2,2′-bithiophene group, exhibited enhanced photovoltaic property as DF-HTMs, including larger backbone planarity, declining highest occupied molecular orbit (HOMO) energy level, increasing hole transportation, more effective passivation, and efficient charge extraction. With fluorinated DFBT-MTP being applied as DF-HTMs in p–i–n PVK-SCs, an efficiency of 20.2% was achieved, showing ∼35% efficiency increase compared with the nonfluorinated BT-MTP-based devices. The leading power conversion efficiency (PCE) indicates that the fluorinated compounds should be a promising direction for exploring high-performance DF-HTMs in the p–i–n PVK-SCs.