Ionic migration induced loss analysis of perovskite solar cells: a poling study

Understanding the interplay between ionic migration and defect trapping in photovoltaic perovskites is critical to develop targeted passivation techniques for performance enhancement. In this study, systematic poling experiments on Cs0.05(FA0.85MA0.15)0.95Pb(I0.85Br0.15)3 perovskite solar cells (PSCs) were conducted to resolve the principal effects of bias dependent pretreatment effects due to dynamic ionic migration. We find that under negative polarizations, iodine ion accumulation at perovskite/electron transport layer (ETL) interfaces causes enhanced global non-radiative recombination in PSCs and significant open-circuit voltage (Voc) losses. On the other hand, dramatic short-circuit current (Jsc) reduction occurs in positively polarized devices, which is ascribed to ineffective charge collection due to modified band-bending towards both charge transport materials. Spatiotemporally scanning probe microscopy on the surface of polarized perovskites provides an in situ estimation of iodine diffusion mobility and visualization of reorganizations under an external bias. Moreover, our findings suggest that the precondition effect of PSCs under operation due to defect ions is recoverable, therefore achieving a respectable lifetime of PSCs for commercialization is promising.