Discerning the Role of an A-Site Cation and X-Site Anion for Ion Conductivity Tuning in Hybrid Perovskites by Photoelectrochemical Impedance Spectroscopy
Priya Srivastava, Ramesh Kumar, Monojit Bag
Abstract
Hybrid perovskite materials are mixed electronic–ionic conductors which enhance the complexity of conduction in these materials. Complete understanding of ionic conductivity along with electronic conductivity is crucial. Herein, we employed photoelectrochemical impedance spectroscopy on a perovskite/electrolyte interface-based device to investigate the role of an A-site cation and X-site halide ion in dictating the charge and ionic conductivity of the perovskite material. It was noted that ionic conductivity of the perovskite material can be tuned either by changing the A-site cation (MA+/FA+) or by changing the X-site halide ion (I–/Br–). Photoinduced ionic conductivity can be significantly different (opposite) in different cation perovskites or different halide-based perovskites. Therefore, mixed-cation perovskites can be utilized to reduce photoinduced ion conductivity. Furthermore, very fine tuning is also possible by modulating with the external applied bias. The influence of ion accumulation and migration on the charge storage and transport property of the device is analyzed using vacancy hopping and the jump relaxation model. Ionic conductivity spectra revealed Jonscher’s law dependence in the mid- and low-frequency range with a constant plateau at high frequencies. It can be concluded that the interplay of ion migration and accumulation decides the resulting conduction and storage property of the complete device. These perovskite/electrolyte-based devices can therefore be promising candidates for electrolyte-gated perovskite field-effect transistors where switchable ion conductivity can be achieved either by photoexcitation or external electric field.