Air fabrication of SnO2 based planar perovskite solar cells with an efficiency approaching 20%: Synergistic passivation of multi-defects by choline chloride

Defects in the perovskite films impose a serious issue on the PCE and stability of the SnO2 based planar perovskite solar cells (SP-PSCs). So far, most researches have focused on regulating the SnO2/perovskite interface to improve performance. However, defect passivation of the perovskite/HTM interface is more significant and potential. Herein, the non-toxic and cheap choline chloride was performed to passivate multiple defects of the MAPbI(3)/HTM interface in ambient atmosphere. An optimal PCE of 19.93% (the average PCE was 18.60%) was obtained for the passivated device. Furthermore, the effect and mechanism of choline chloride on the humid and thermal stability of the SP-PSCs was investigated in detail. The passivated device without encapsulation retained 91% of its initial efficiency after 20 days in humid environment (20 +/- 5 degrees C, 55 +/- 5% RH) and 95% of the initial value under heating for 7 cycles (85 degrees C). Chloride ions with smaller radius and larger electronegativity formed stronger ionic bonding with Pb2+ to passivate I- vacancy defects, while choline ions passivated MA(+) vacancies. This work not only provides guidance for fabrication of an efficient and stable device in air, but also opens an avenue to understanding of relation between stability and defects in the SP-PSCs.