Characteristic voltages and times from capacitance–voltage analysis of quantum dot light-emitting diodes

Abstract

The characteristic voltages in the capacitance–voltage (C–V) curve of quantum dot light-emitting diodes (QLEDs) are usually linked to the start of charge injection and recombination in a working device. However, it may lead to a misunderstanding of the carrier process in QLEDs. This is because capacitance change only reflects an electrical response of additional carriers induced by a small signal loaded on an applied DC voltage but does not directly correlate with the total free carrier response governed by the working voltage. In this work, we study the frequency-dependent C–V characteristics of a blue QLED, focusing on the characteristic voltages, characteristic times, and their relationships. First of all, we identify that the charge injection point of QLEDs should be extracted by the current density–voltage–luminance characteristics rather than the C–V curve. As for the characteristic voltages obtained from the C–V curve, they are determined by voltage-dependent characteristic times in different time domains. Furthermore, the C–V characteristic is helpful to evaluate charge accumulation or leakage in blue QLED, serving as an accessible analysis tool in the carrier transport process. Our work provides a definite physical meaning of characteristic voltages in the C–V curve and exhibits the usefulness of C–V characteristics for analyzing the charge dynamics of QLED.