High-efficiency perovskite solar cells with imidazolium-based ionic liquid for surface passivation and charge transport.

Surface defects have been a key constraint for perovskite photovoltaics. Herein, 1,3-dimethyl-3-imidazolium hexafluorophosphate (DMIMPF 6 ) ionic liquid (IL) is adopted to passivate the perovskite surface and also reduce the energy barrier between the perovskite and hole transport layer. Theoretical simulation and experimental results demonstrate that Pb-cluster and Pb-I antisite defects can be effectively passivated by [DMIM] + bonding with the Pb 2+ on the perovskite surface, leading to significantly suppressed non-radiative recombination. As a result, the solar cell efficiency is increased to 23.25% from 21.09% for the control device, mostly due to improvement of open-circuit voltage. Furthermore, the DMIMPF 6 -treated perovskite device shows better long term environmental stability because the DMIMPF 6 layer can efficiently block moisture permeation due to its hydrophobic nature. This work provides firm support to the understanding of the passivation effect and further promotes the development of surface engineering for enhancing the performance of perovskite photovoltaics.