Suppressing Ion Migration across Perovskite Grain Boundaries by Polymer Additives

Passivation of organometal halide perovskites with polar molecules has been recently demonstrated to improve the photovoltaic device efficiency and stability. However, the mechanism is still elusive. Here, it is found that both polymers with large and small dipole moment of 3.7 D and 0.6 D have negligible defect passivation effect on the MAPbI(3)perovskite films as evidenced by photothermal deflection spectroscopy. The photovoltaic devices with and without the polymer additives also have comparable power conversion efficiencies around 19%. However, devices with the additives have noticeable improvement in stability under continuous light irradiation. It is found that although the initial mobile ion concentrations are comparable in both devices with and without the additives, the additives can strongly suppress the ion migration during the device operation. This contributes to the significantly enhanced electrical-field stress tolerance of the perovskite solar cells (PVSCs). The PVSCs with polymer additives can operate up to -2 V reverse voltage bias which is much larger than the breakdown voltage of -0.5 V that has been commonly observed. This study provides insight into the role of additives in perovskites and the corresponding device degradation mechanism.

Automated summary

While the passivation effect of polymers with large and small dipole moments on MAPbI(3) perovskite films is negligible, they can significantly improve the stability of photovoltaic devices under continuous light irradiation. The additives are able to strongly suppress ion migration, enhancing the electrical-field stress tolerance of perovskite solar cells.