Negative capacitance in organic light-emitting diodes

Negative capacitance has been characterized in organic light-emitting diode (OLED) heterostructures using impedance spectroscopy. Although similar inductive behavior has been previously reported for transient electroluminescence in OLEDs, definitive identification of negative capacitance in impedance spectroscopy data has been elusive due to the high concentration of distributed traps at the anode-organic interface. The addition of a layer of 4,4′-bis[(p-trichlorosilylpropylphenyl)phenylamino]-biphenyl at this interface minimizes these trapping sites, thus enabling the inductive nature of charge transport in OLEDs to be directly observable. By quantitatively correlating the resulting impedance spectroscopy data with equivalent circuit models, a detailed description of charge transport in OLEDs as a function of heterostructure composition is developed.