ac Impedance Characteristics and Modeling of Polymer Solution Light-Emitting Devices

Recently, we demonstrated polymer solution light-emitting devices (SLEDs) using polymeric solutions as the light-emitting medium. The operating mechanism of the SLED was proven to be electrogenerated chemiluminescence (ECL). In this manuscript, we report the results obtained from ac impedence studies on the SLED. Based on the results, the SLED can be modeled as a combination of device capacitance (C1), solution layer resistance (R1), interfacial capacitance (C2), and interfacial resistance (R2). It was found that the impedance characteristics of the SLED are a strong function of the bias voltage. At low bias voltages, the impedance plots exhibited semicircular and linear characteristics in the high- and low-frequency range, respectively. With increase in the bias voltage, C2 decreased, implying an ECL mechanism for the SLED. Finally, an interesting behavior was observed when the SLED was biased at 8 V. The impedance spectrum was similar to that of the solid-state polymer light-emitting electrochemical cell (LEC), suggesting some similarities in the device operating mechanism between the SLED and LEC