Probing the Origin of Light-Enhanced Ion Diffusion in Halide Perovskites

Organic-inorganic hybrid halide perovskites have emerged recently as highly promising materials for optoelectronics such as photovoltaics and photodetectors. A unique feature of these materials is ion diffusion that directly impacts the optoelectronic process by affecting the charge transport and trapping. In order to shed light on the ionic diffusion behavior, the hybrid perovskites MAPbI₃ and MAPbI₃ with minor doping of phenyl-C61-butyric acid methyl-ester (MAPbI₃-PCBM) thin-film capacitors were investigated in the presence of steady and dynamic visible illumination of different intensities. Light-induced capacitance, which increases monotonically with the increase of light intensity, was observed in the low-frequency range below 300 kHz of the electric field on both while differing quantitatively. Specifically, the large light-induced capacitance in the MAPbI₃ capacitors can be obtained in the MAPbI₃-PCBM ones in the dark. In addition, the increase of capacitance with light intensity is much less in the latter with electron trapping induced by PCBM. This result has revealed that the light-induced capacitance in MAPbI₃ capacitors can be ascribed to the contribution of the additional charges across the capacitors associated with ionic diffusion activated by the illumination and that the effects on the capacitance will remain after the illumination is turned off due to residual photoexcited electrons trapped in the MAPbI₃-PCBM sample.