Efficient surface treatment based on an ionic imidazolium hexafluorophosphate for improving the efficiency and stability of perovskite solar cells

Surface defects have been a primary limitation for perovskite solar cells (PSCs). Herein, the introduction of 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6) into the perovskite surface with the help of isopropanol (IPA) solvent can passivate the surface defects. The surface reconstruction of perovskite caused by IPA makes it easier for [BMIM](+) to passivate uncoordinated Pb2+ defects, [PF](6)(-) to more easily replace and compensate unstable I-/Br- ions and I-/Br- vacancies. This forms large perovskite grains and island-like Cs-0.05(MA(0.12)FA(0.88))(0.95)Pb(I0.88Br0.12)(3-x)(PF6)(x) interlayers, which significantly reduces the defect-states density and inhibits recombination, and the energy barrier for the perovskite and the hole transport layer is also lowered. As a result, the open-circuit voltage was elevated from 1.112 to 1.181 V, and the efficiency for solar cells was also increased from 19.01% to 21.51%. In addition, the surface treatment of the hydrophobic BMIMPF6 can isolate the erosion of moisture and obtain better stability.