Low Threshold Voltage and Carrier Injection Properties of Inverted Organic Light-Emitting Diodes with [Ca₂₄Al₂₈O₆₄]⁴⁺(4e⁻) Cathode and Cu_2−<i>x</i>Se Anode

Abstract

Carrier injection properties including threshold voltages of inverted top-emission organic light-emitting diodes (ITOLED) were improved by applying room temperature stable electride [Ca24Al28O64]4+(4e−) (C12A7:e−), which has a low work function of ∼2.4 eV, and a p-type degenerated semiconductor Cu2−xSe to bottom cathode and top anode buffer layers, respectively. The formation of a low-barrier electron injection contact between C12A7:e− and tris(8-hydroxyqunoline)aluminum (Alq3) is demonstrated by the current−voltage characteristics of electron-only devices, as well as by photoelectron spectroscopy. The threshold voltage of the ITOLED is reduced by changing the bottom cathode from Al to C12A7:e− from 9 to 7.6 V at 10 mA cm−2. A 5 nm thick Cu2−xSe top anode buffer layer, deposited at room temperature, reduced the threshold voltage further to ∼2 V. The luminance efficiency of ITOLED with a Cu2−xSe buffer layer is nearly twice as large as that without the buffer layer. We emphasize that developing new electrode materials is an effective means to improve the performance of not only OLED but also other new optoelectronic devices.