Correlations of Ionic Migration and Deep-Level Traps Leads to Surface Defect Formation in Perovskite Solar Cells

Abstract

Correlations between ion migration, charge carrier, and bulk deep-level defect in MAPbI3 perovskites are systematically invesitgated through voltage-dependent thermal admittance spectroscopy and in situ scanning probe microscopy. We show that iodine interstitials construct stable, deep-level bulk defects in the polycrystalline MAPbI3 with an activation energy (EA) level of 0.495 eV above the valence band maximum. Experimentally, EA varied with depletion region distribution and excess electron from charge transport layers, which can be modulated through external bias. Under forward bias, mobile bulk defects migrate and transform into surface defect states, introducing additional nonradiative recombination pathways. Overall, this study directly reveals electronic correlations between defect ions and charge carriers, pointing out the importance of iodine defect chemistry in surface recombination and degradation in long-term device stabilities.