Correlations between Immobilizing Ions and Suppressing Hysteresis in Perovskite Solar Cells

Ion migration has been regarded as the major cause of photocurrent hysteresis. Here we use photoluminescence (PL) and optical images, combined with Galvanostatic measurement, to detect the ionic motion. We observe an irreversible PL and optical transmittance change after electric poling. By comparing a neat perovskite film with the sample coated by poly(methyl methacrylate) (PMMA), polyethylene glycol (PEG), and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), we found that PCBM effectively inhibits ionic motion near the surface of the perovskite.We further evidenced the donor-acceptor complex formed between PCBM and perovskite, implying the mechanism of inhibited ion migration by PCBM. We close by demonstrating that PCBM can also be introduced on the top of perovskite fim in an n-i-p TiO₂ planar structure, to achieve an average 14% steady-state output over 2.3 × 10⁵ s (∼64 h). This work highlights the importance of inhibiting ionic motion in perovskite solar cells.