Origin of Anomalous Capacitive Behaviour in Perovskite Light Emitting Diodes

Owing to the exceptional optoelectronic properties, Hybrid halide perovskites (HHPs) have attracted great attention leading to the variegated application in optoelectronic devices ¹. Study of carrier kinetics in perovskite solar cells using Impedance Spectroscopy (IS) has been the topic of research since the last few years². But, research in Perovskite LEDs (PeLEDs) is still sparse.
Here, we have studied the charge carrier kinetics of PeLEDs using IS at different applied bias. The electrical equivalent circuit of the device was modelled and the variation of different parameters with applied bias was studied. We have observed the bias dependent transition of capacitance from positive to negative at low frequency. The inflection point along with the magnitude of this negative capacitance depends significantly on the morphology of the perovskite film. We have also observed anomalous capacitive behaviour for the first time at high frequency due to the interplay between electronic and ionic charge transport. We have proposed a possible model responsible for anomalous capacitive behaviour and its correlation with active layer morphology in PeLEDs.
References
1. Lin, K. et al. Nat. 562.7726, 245 (2018)
2. Bag, M. et al. J. Am. Chem. Soc. 137, 13130-13137 (2015)