Srivastava Priya, Bag Monojit
Advanced Research in Electrochemical Impedance Spectroscopy, Department of Physics, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand 247667, India.
Phys Chem Chem Phys. 2020 May 20;22(19):11062-11074. doi: 10.1039/d0cp00682c.
Charge transport through lead trihalide based perovskites is more complex than through any other semiconducting materials due to their mixed electronic-ionic conductivity as well as ambipolarity. Here we have investigated charge transport through a perovskite/electrolyte interface using electrochemical impedance spectroscopy (EIS) under illumination and applied bias conditions. Similar trends in EIS were observed with positively biased as well as negatively biased working electrodes, indicating ambipolar charge transport through the perovskite layer. Ionic conductivity upon photo-illumination plays a significant role in modulating charge transport at the interface by creating an additional built-in field which flips its polarity at a moderate applied bias voltage. Therefore, anomalous charge transport resistance is observed under illumination at around 400 to 600 mV applied bias. Electric field induced UV-Vis absorption spectroscopy shows a decrease in absorption when both positive and negative bias voltages are applied to a perovskite coated ITO working electrode, indicating the occurrence of excited state charge transfer at the electrolyte interface. Two distinct electric field induced bleaching bands have been observed at around 480 nm and 750 nm, similar to the two photobleaching bands due to the dual nature of the excited states in lead halide perovskites.
由于铅卤化物基钙钛矿具有混合的电子 - 离子导电性以及双极性，通过它们的电荷传输比通过任何其他半导体材料都更复杂。在这里，我们使用电化学阻抗谱（EIS）在光照和施加偏压条件下研究了通过钙钛矿/电解质界面的电荷传输。在正偏置和负偏置工作电极下观察到EIS有类似趋势，表明通过钙钛矿层的双极性电荷传输。光照下的离子导电性通过创建一个额外的内建电场在调节界面处的电荷传输中起重要作用，该电场在中等施加偏压下会翻转其极性。因此，在施加约400至600 mV偏压的光照下观察到异常的电荷传输电阻。电场诱导的紫外 - 可见吸收光谱表明，当向涂有钙钛矿的ITO工作电极施加正偏压和负偏压时，吸收都会降低，这表明在电解质界面发生了激发态电荷转移。在约480 nm和750 nm处观察到两个不同的电场诱导漂白带，类似于由于卤化铅钙钛矿中激发态的双重性质而产生的两个光漂白带。
