Passivation with Ion Polarization for Perovskite Solar Cells

Surface defects of metal halide perovskite increase the non-radiative recombination and cause the loss of the power conversion efficiency (PCE) in perovskite solar cells (PSCs). In this work, we introduce an effective passivation on FAPbI 3 perovskite with 2D perovskite in which the halogen anions are polarized by the alkaline earth metal cations. The best open-circuit voltage (V oc ) of PSCs increases from 1.02 V to 1.10 V by the passivation of (MgBr) 2 PbI 4 , and accordingly PCE rises from 19.63% to 23.08%. It is found that the hole extraction ratio rises from 8.92% in the control FAPbI 3 /Spiro-OMeTAD interface to 45.33% in the passivated FAPbI 3 /(MgBr) 2 PbI 4 /Spiro-OMeTAD interface because of the surface repair of the perovskite film. As a consequence, the non-radiative recombination of charge carriers decreases drastically from 89.82% to 54.55% due to the drop of charge accumulation at the interface. Significantly, the effect of passivation will be improved with the increase of polarization ability of alkaline earth metal ions. Passivation of (MgBr) 2 PbI 4 has a rise of about 5% in PCE compared with that of (CaBr) 2 PbI 4 . The role of ion polarization in the perovskite lies in the enhancement of the covalence property, leading to stronger binding of halogen anions by alkaline earth metal cations and inhibition of the formation of their vacancies.