Revealing the Correlation of Light Soaking Effect with Ion Migration in Perovskite Solar Cells

Light soaking (LS) effect of perovskite solar cells (PSCs), i.e., the power conversion efficiency (PCE) increases under continuous light illumination (CLI), has attracted a lot of attention recently. Herein, it is reported that a strong LS effect occurs in the FA x MA 1‐x PbI 3 (FAMA) PSC for its PCE increases from 7.5% to 20.5% under CLI. Based on the dynamics of the LS effect, drift‐diffusion simulations, and external voltage experiments, it is found that the underlying process for the LS effect is that the generated photovoltage under CLI modulates the distribution of mobile ions in absorber layers increasing charge extraction ability and then alleviating interface recombination, which directly results in the LS effect in FAMA PSCs. In addition, the introduction of Cs + into perovskite films can reduce the density of accumulated mobile ions at the interface between absorber layers and charge‐transporting layers in FAMA PSCs. As a result, the PCE of the Cs + ‐doped device increases from 18.7% to 22.4% under CLI demonstrating that the LS effect in the Cs + ‐doped device is suppressed notably. This work reveals the correlation of the LS effect with ion migration and suppresses the LS effect in FAMA PSCs.