Molecular Doping of a Hole-Transporting Material for Efficient and Stable Perovskite Solar Cells

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)CI 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)CI developed for Spiro-OMeTAD in this work can effectively meet the demands of future photovoltaic applications with promising efficiency and device stability.