Picosecond Capture of Photoexcited Electrons Improves Photovoltaic Conversion in MAPbI :C -Doped Planar and Mesoporous Solar Cells.

In this work, solar cells based on methylammonium lead iodide (MAPbI ) doped in solution with C fullerene in a mesoporous as well as planar electron-transporting layer (ETL)-free architecture are realized, showcasing in the latter case a record efficiency of 15.7% and an improved open-circuit voltage (V ). Contrary to the bulk heterojunction previously reported, the C molecules do not phase segregate and they are rather finely dispersed in the perovskite film, possibly infiltrating at the grain boundaries, while assisting the growth of a highly uniform perovskite layer. By means of time-resolved femtosecond-to-nanosecond optical spectroscopy, with an extended spectral coverage, it is observed that electrons photogenerated in the perovskite are transferred to C with a time constant of 20 ps. Despite being captured by C , electrons are not deeply trapped and can potentially bounce back into the perovskite, as suggested by the high fill factor and enhanced V of the MAPbI :C solar cells, especially in the case of the ETL-free device configuration.