Efficient and stable one-micrometre-thick organic light-emitting diodes

Organic light-emitting diodes (OLEDs) with thick carrier transport layers are desirable for high production yields of OLED-based displays and lighting; however, high operating voltages are inevitably introduced to thick OLEDs due to the low carrier mobilities of organics. The associated Joule heating will also induce structural defects and lower operational stabilities. Here we demonstrate highly efficient and stable OLEDs with thicknesses of over 1 μm and low operating voltages. The OLEDs use MoO₃/SimCP2 as a hole-injection layer and a thick layer of 4,4′-(cyclohexane-1,1-diyl)bis(N,N-di-p-tolylaniline) (TAPC) as a hole-transporting layer. We find that Ohmic hole injection can only be formed for TAPC layers with thicknesses of over 900 nm. In this configuration, we achieve external quantum efficiencies of 23.09%, 22.19% and 7.39%, and operating voltages of 5.11 V, 3.55 V and 6.88 V at 1,000 cd cm^–2 for red, green and blue OLEDs, respectively. We also incorporate a thin layer of HAT-CN between the TAPC and electron-blocking layers to suppress electron leakage. The red, green and blue OLEDs in this work maintained the above-mentioned performances while also featuring excellent extrapolated LT₉₅ operational lifetimes of around 55,000 h, 18,000 h and 1,600 h, respectively, at an initial luminance of 1,000 cd cm^–2. We believe that our work paves the way for large-area OLED-based displays and lighting with high production yields.