Molecular Doping of a Hole-Transporting Material for Efficient and Stable Perovskite Solar Cells
Junsheng Luo, Jinqing Zhu, Fangyan Lin, Jianxing Xia, Hua Gui Yang, JinyuYang, Ruilin Wang, Junyu Yuan, Zhongquan Wan, Ning Li, Christoph J. Brabec, Chunyang Jia
Abstract
The bis(trifluoromethane)sulfonimide lithium salt (Li-TFSI) is commonly used as an effective dopant to improve the conductivity and hole mobility of Spiro-OMeTAD in state-of-the-art n–i–p perovskite solar cells (PSCs). However, such doping severely induces device instability because of the ultrahygroscopic and migratory nature of Li+ ions. Here, we demonstrate a fluorinated Fe(F20TPP)Cl with a hydrophobic property and a high migration barrier as a potential alternative to replace the Li-TFSI in doped Spiro-OMeTAD. The optimized PSCs show a champion power conversion efficiency as high as 21.53% with a stabilized efficiency exceeding 21%. In addition, long-term stability of PSCs is significantly improved, and the device retains 84% of its initial efficiency after 900 h under continuous 100 mW cm–2 white light-emitting diode illumination and 89% of its initial efficiency after even 50 days in an ambient environment without encapsulation. We believe that this work addresses the fundamental question of intrinsic and extrinsic instability in Li-TFSI-based PSCs by combining simulation and experimental studies. The novel dopant Fe(F20TPP)Cl developed for Spiro-OMeTAD in this work can effectively meet the demands of future photovoltaic applications with promising efficiency and device stability.