Formation of ultrasmooth perovskite films toward highly efficient inverted planar heterojunction solar cells by micro-flowing anti-solvent deposition in air†

Ultrasmooth perovskite thin films are prepared by a solution-based one-step micro-flowing anti-solvent
deposition (MAD) method carried out in air with simplicity and practicability. Engaging inert gas blow and
anti-solvent drips as accelerators, ultrafast crystallizing, thickness controllable, and high quality
methylammonium lead iodide films are prepared with a least root mean square roughness of 1.43 nm
(1.95 nm on average), achieving the smoothest surface morphology to the best of our knowledge, as
well as a rather compact perovskite layer with a high coverage ratio. Perovskite films formed from MAD
require no annealing procedure to ultimately crystallize, realizing a very fast crystallizing procedure
within few seconds. By controlling the thickness of perovskite films, superior photovoltaic performance
of solar cells with a large fill factor of 0.8 and a PCE of 15.98% is achieved without a glovebox. MAD
technology will benefit not only highly efficient photovoltaic devices, but also perovskite-based hybrid
optoelectronic devices with field effect transistors and light emitting diodes as well.