Efficient and Stable Perovskite Solar Cells by Fluorinated Ionic Liquid-Induced Component Interaction

The instability of organic cations in lead halide perovskite materials is a major obstacle for the commercial breakthrough of perovskite photovoltaics due to desorption of organic cations during the thermal annealing and device operation. Herein, a novel strategy is reported to improve the performance and stability of organic halide perovskite solar cells containing organic cations by adding a small amount of the ionic liquid methylammonium difluoroacetate (MA(+)DFA(-)). Nuclear magnetic resonance and Fourier-transform infrared spectroscopy measurements show that MA(+)DFA(-) can anchor the organic cations via hydrogen bonding and enhance the Pb-O interaction in perovskite precursors, leading to the retardation of the perovskite crystallization and improved stability of the perovskite precursor solution. Dynamic light scattering and scanning electron microscopy verify the defect-passivation effect of MA(+)DFA(-) on the perovskite precursors and films. The passivated perovskite film shows superior photo carrier dynamics as investigated by time-resolved photoluminescence and transient absorption spectra. Moreover, the hydrogen bonding of the perovskite with MA(+)DFA(-) imparts excellent ambient and thermal stability to the film as revealed by X-ray diffraction measurements. As a result, devices with a high efficiency of 21.46% and excellent stability over 180 days in nitrogen atmosphere at room temperature are achieved with the ionic liquid.

Automated summary

A novel strategy to enhance the performance and stability of organic halide perovskite solar cells by adding a small amount of the ionic liquid MA(+)DFA(-) is reported. The ionic liquid can anchor the organic cations via hydrogen bonding and improve the Pb-O interaction, leading to improved stability and superior photo carrier dynamics. Devices with high efficiency and excellent stability over 180 days in a nitrogen atmosphere at room temperature are achieved with the ionic liquid.