Abstract
In our previous paper [T. Matsushima et al., Nature 572, 502 (2019)], current densities of organic light-emitting diodes (OLEDs) did not decrease significantly when the thicknesses of a 1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile (HAT-CN) transport layer were increased from tens of nanometers to 1 μm. To make this mechanism clear, we carried out several experiments in terms of electron transfer with other organic layers and electron mobility of HAT-CN. Finally, we found that the vacuum-evaporated HAT-CN layers have very high electron mobility and, therefore, using a HAT-CN transport layer can suppress the decrease in current density even in thick OLEDs. The electron mobility of vacuum-deposited HAT-CN layers, which was measured using analysis with a space-charge-limited current model, was 0.1–1 cm2 V−1 s−1. This electron mobility is much higher than those of conventional organic transport layers used in OLEDs (<10−3 cm2 V−1 s−1) even though the HAT-CN layers are amorphous-like. We attributed one of the reasons for this extraordinarily high mobility to be a better overlap of π orbitals in the substrate normal, which is associated with horizontally oriented HAT-CN molecules on a substrate.
Highlights
Performance of organic light-emitting diodes (OLEDs) has been developed to a level for practical applications such as displays and lighting
Using thin organic layers is important for OLEDs as we mentioned earlier, an issue that frequently arises in OLEDs is the difficulty of uniformly covering a substrate with thin organic layers
HAT-CN has been widely used as the buffer layer between the indium tin oxide (ITO) anode layer and the organic hole transport layer in OLEDs
Summary
Performance of organic light-emitting diodes (OLEDs) has been developed to a level for practical applications such as displays and lighting. This again points to the importance of decreasing the organic layer thickness for achieving the high current injection into OLEDs. scitation.org/journal/adv
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