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Synergistic Effect of Fluorinated Passivator and Hole Transport Dopant Enables Stable Perovskite Solar Cells with an Efficiency Near 24%

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journal contribution
posted on 18.02.2021, 17:11 authored by Hongwei Zhu, Yameng Ren, Linfeng Pan, Olivier Ouellette, Felix T. Eickemeyer, Yinghui Wu, Xianggao Li, Shirong Wang, Hongli Liu, Xiaofei Dong, Shaik M. Zakeeruddin, Yuhang Liu, Anders Hagfeldt, Michael Grätzel
Long-term durability is critically important for the commercialization of perovskite solar cells (PSCs). The ionic character of the perovskite and the hydrophilicity of commonly used additives for the hole-transporting layer (HTL), such as lithium bis­(trifluoromethanesulfonyl)­imide (Li-TFSI) and tert-butylpyridine (tBP), render PSCs prone to moisture attack, compromising their long-term stability. Here we introduce a trifluoromethylation strategy to overcome this drawback and to boost the PSC’s solar to electric power conversion efficiency (PCE). We employ 4-(trifluoromethyl)­benzylammonium iodide (TFMBAI) as an amphiphilic modifier for interfacial defect mitigation and 4-(trifluoromethyl)­pyridine (TFP) as an additive to enhance the HTL’s hydrophobicity. Surface treatment of the triple-cation perovskite with TFMBAI largely suppressed the nonradiative charge carrier recombination, boosting the PCE from 20.9% to 23.9% and suppressing hysteresis, while adding TFP to the HTL enhanced the PCS’s resistance to moisture while maintaining its high PCE. Taking advantage of the synergistic effects resulting from the combination of both fluoromethylated modifiers, we realize TFMBAI/TFP-based highly efficient PSCs with excellent operational stability and resistance to moisture, retaining over 96% of their initial efficiency after 500 h maximum power point tracking (MPPT) under simulated 1 sun irradiation and 97% of their initial efficiency after 1100 h of exposure under ambient conditions to a relative humidity of 60–70%.