Passivation with Ion Polarization for Perovskite Solar Cells

Surface defects of metal halide perovskite increase the non-radiative recombination and cause loss of the power conversion efficiency (PCE) in perovskite solar cells (PSCs). In this work, we introduce an effective passivation on FAPbI₃ perovskite using 2D perovskites in which halogen anions are polarized by 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)₂PbI₄, and accordingly PCE rises from 19.63% to 23.08%. It is found that the hole extraction ratio rises from 8.92% at the control FAPbI₃/Spiro-OMeTAD interface to 45.33% at the passivated FAPbI₃/(MgBr)₂PbI₄/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 is improved with the increase of polarization ability of alkaline earth metal ions. Passivation of (MgBr)₂PbI₄ has a rise of about 5% in PCE compared with that of (CaBr)₂PbI₄. The role of ion polarization in perovskites 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 halogen vacancies.