Over 12% efficient CsSnI3 perovskite solar cells enabled by surface post-treatment with bi-functional polar molecules

Eco-friendly all-inorganic tin halide perovskite compounds have drawn significant attention for photovoltaic applications. Nevertheless, the non-radiative recombination derived from the uncoordinated Sn2+ cations at surface and the electron extraction barrier between different functional layers significantly impair the performance of perovskite device. Here we for the first time show that thiophene derivative, 3-thiophenemethylammonium iodide, as an interface modifier between the CsSnI3 perovskite surface and electron transport layer, can passivate defects and reduce the electron extraction potential barrier. The molecules of 3-thiophenemethylammonium iodide can autonomously inter-connect with uncoordinated Sn2+ via lone electron pairs of the donated π electrons in electronic-rich thiophene molecule. Moreover, such interface modifier lowers the electron extraction potential barrier at the perovskite/electron transport layer junction in which an interface dipole electric field form. Consequently, the optimized planar solar cell with a structure of ITO/PEDOT:PSS/CsSnI3/ICBA/BCP/Ag, exhibited a power conversion efficiency of 12.05 % under AM 1.5G illumination condition. To the best of our knowledge, this is the highest efficiency for fully inorganic CsSnI3-based devices reported so far. This study represents an innovative approach to realize high-efficiency all-inorganic CsSnI3 perovskite solar cells.