A 1,4,5,8,9,11-hexaazatriphenylenehexacarbonitrile (HAT-CN) transport layer with high electron mobility for thick organic light-emitting diodes

• Main Authors: Kenta Yamaguchi, Yu Esaki, Toshinori Matsushima, Chihaya Adachi
• Format: Article
• Language: English
• Published: AIP Publishing LLC 2020-05-01
• Series: AIP Advances
• Online Access: http://dx.doi.org/10.1063/5.0007310

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.