Enhanced Hole-Injection Property in an OLED with a Self-assembled Monolayer of Hole-Transporting TPD on Thin Au as the Anode

Abstract

A thioester-functionalized triphenylamine hole-transporting molecule (TPD-SAc) was synthesized and self-assembled to form a monolayer on an ultra-thin Au film supported on indium-tin oxide glass. The modified surface was characterized by aqueous contact angle, ellipsometer, atomic force microscopy, X-ray photoelectron spectroscopy, and ultraviolet photoelectron spectrometer to substantiate the formation of compact and pinhole-free monolayers. The modified organic light emitting diode device [indium-tin oxide/Au (5 nm)/self-assembled monolayers (SAM)/TPD (50 nm)/Alq₃ (40 nm)/TPBI (15 nm)/LiF (1 nm)/Al (100 nm)] showed a luminance of 7303.90 cd/m² and a current efficiency of 8.49 cd/A with 1.78 and 2.29-fold increase, respectively, compared to the control device without SAM. The improvements were attributed to the enhanced compatibility of the organic–inorganic interface, matched energy level by introduction of an energy mediating step and superior hole-injection property of SAM molecules.

Keywords

TPD-SAc / Au / Self-assembled monolayer / Organic light emitting diode / Hole injection

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