Unveiling the Interfacial Properties of Organic Single-Crystal Hole-Transporting Layers for High-Performance Light-Emitting Devices

Abstract

Organic single crystals with long-range molecular periodic ordering ensure superior charge-transport properties and low defect density, which have been considered promising candidates for charge-transporting materials in organic light-emitting devices (OLEDs). The functional interfaces of OLEDs play a critical role in charge-transporting and light-emitting behaviors, while the interfacial properties of organic single crystals in OLEDs and their impact on device performance have been rarely investigated. Herein, two typical organic single crystals, 1,4-bis(4-Methylstyryl)benzene (BSB-Me) and 2,6-diphenylanthracene (DPA) with different molecular formulas and packing structures, are introduced as the single-crystal hole-transporting layers (HTLs) for a systematic investigation of the interfacial properties between single-crystal HTLs and active emissive layers. BSB-Me single-crystal HTLs offer satisfied surface wettability and enhanced interfacial interaction, which dominate the charge-transporting and light-emitting behaviors of the OLEDs. Such improved interfacial properties are responsible for the superior light out-coupling efficiency of BSB-Me single-crystal OLEDs with efficient exciton recombination and minimal Joule heat loss. In consequence, BSB-Me single-crystal OLEDs exhibit a maximum luminance of 50,170 cd/m² and a peak EQE of 8.78%, which are better than DPA-based devices. Furthermore, BSB-Me single-crystal HTLs with favorable interfacial properties enable large-area OLEDs with uniform EL emission over the whole light-emitting area of 1 mm × 1 mm.

Keywords

electroluminescence / interfacial properties / OLEDs / organic single crystals / single-crystal HTLs

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