Implementation of graphene multilayer electrodes in quantum dot light-emitting devices

Abstract

Graphene is a highly attractive candidate for implementation as electrodes in next-generation large-area optoelectronic devices thanks to its high electrical conductivity and high optical transparency. In this study, we show all-solution-processed quantum dot-based lightemitting devices (QD-LEDs) using graphene mono-and multilayers as transparent electrodes. Here, the effect of the number of graphene layers (up to three) on the QD-LEDs performance was studied. While the implementation of a second graphene layer was found to reduce the turn-on voltage from 2.6 to 1.8 V, a third graphene layer was observed to increase the turn-on voltage again, which is attributed to an increased roughness of the graphene layer stack.

Transparent Conducting Electrodes for Quantum Dots Light Emitting Diodes

“…predicted that the sheet resistance and transmittance of graphene would be Rs∼62.4/N Ohm/square and T∼100–2.3 N %, respectively, and that these properties would vary with a number of layers (N). As shown in Figure a and b, the experiments appeared to support their predictions …”

“…As shown in Figure 16a and b, the experiments appeared to support their predictions. [103] Graphene also has high optical transmittance owing to its thinness (0.34 nm), [104] and besides its excellent optical transmittance and electron conductivity, graphene has good thermal and chemical resistance, outstanding mechanical properties, and good interfacial contact with organics. [105][106][107] These properties make graphene a promising candidate to replace current TCEs for next-generation flexible QDLEDs.…”

“…In addition to the optical transmittance and sheet resistance, graphene-based TCEs for QDLEDs must satisfy unique device requirements and need to reduce roughness to enhance interfacial contact between electrode and cell and work more efficiently. For instance, Wolff et al [103] conducted an experiment to show the relationships between graphene roughness, number of layers, and QDLED performance ( Figure 16) when graphene TCEs were used as the anodes in the bottom layers of QDLEDs. As shown in Figure 16c, increasing the roughness of graphene film by increasing the graphene layer increased the turn-on voltage and decreased the intensity of QDLEDs despite the decreased sheet resistance with the increased graphene layer.…”

“…In addition to the optical transmittance and sheet resistance, graphene‐based TCEs for QDLEDs must satisfy unique device requirements and need to reduce roughness to enhance interfacial contact between electrode and cell and work more efficiently. For instance, Wolff et al . conducted an experiment to show the relationships between graphene roughness, number of layers, and QDLED performance (Figure ) when graphene TCEs were used as the anodes in the bottom layers of QDLEDs.…”

Quantum dot light-emitting diodes with an Al-doped ZnO anode

“…As commonly seen in OLEDs [19], an AZO electrode can avoid the diffusion of indium elements into the device; thus, a similar effect can be expected in QLEDs. In QLEDs, for example, Lin et al constructed an inverted green QLED device based on AZO electrodes by the DC MS method, in which the maximum EQE reached 2.3% at an emission peak at 535 nm [32] A smooth and flat surface electrode is the key factor in constructing QLEDs to produce a homogeneous charge carrier injection and electric field, and high performance [34][35][36]. For instance, Wolff et al [34] discussed the relationship between the turn-on voltage of QLED performance and the graphene roughness.…”