Metal halide perovskite solar cells (PSCs) are emerging
photovoltaic
technology that have attracted worldwide attention owing to their
potential to disrupt the established market of silicon solar cells.
Despite much effort, several lingering issues, such as device efficiency
and stability, are still needed to be solved for the commercial application.
Ionic liquids with unique properties, such as high ionic conductivity,
good thermal stability, and chemical designability, have shown to
play multiple functions for high-efficiency and stable PSCs. In this
Review, we first introduce the structure and property of typical ionic
liquids. Then, we comprehensively discuss the various applications
of ionic liquids and their derivatives in perovskite layers, hole-transporting
layers (HTL), and electron-transporting layers (ETL) of PSCs, as additives,
solvents, dopants, surface modifiers and independent charge-transporting
materials, with particular emphasis on the interaction between ionic
liquids and function layers of PSCs, such as hydrogen bonds, ionic
bonds, coordinate bonds, and so on, as well as the relationship between
molecular structures of ionic liquids and the photovoltaic performances
of PSCs. Finally, we address the conclusions and an outlook for the
future development of this field. It is expected that this Review
will stimulate a generation of new thoughts and ideas on the emerging
challenges and opportunities of ionic liquids-based PSCs.
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.
Organic inorganic lead halide perovskite solar cells (PSCs) offer promising aspects like high efficiency, low-cost and flexible light harvesting devices. The booming growth of PSCs cannot be achieved without the...
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