High Efficiency Non‐Doped White Organic Light Emitting Diodes Based on a Bilayer Interface‐Exciplex Structure

Abstract

High efficiency non-doped blue and white organic light emitting diodes (OLEDs) are realized by using a bilayer interface-exciplex (i-Exc) structure. Since the neutral exciplex are formed at the interface, the interface charge accumulation is reduced, thereby suppressing exciton quenching in the device. With the i-Exc structure, a maximum external quantum efficiency (EQE) of 23.1% is achieved in the non-doped blue phosphorescent OLED. Moreover, the white emission can be obtained by inserting an ultrathin orange-red phosphorescent emitter into the blue devices. The charge trapping in the orange-red emitter can be suppressed by adjusting the position of the ultrathin orange-red emitting layer in the device, contributing to superior spectral stability. The WOLED achieves an EQE of 20.0% and exhibits a stable warm white emission. The Commission Internationale de l'Eclairage (CIE) coordinates of WOLED are (0.41, 0.40) at 5 V and slightly change to (0.40, 0.41) at 9 V.

Recent progress on organic light-emitting diodes with phosphorescent ultrathin (<1nm) light-emitting layers

“…When a phosphorescent UEML was inserted in heterojunction interface, a more efficient energy transfer occurs from interfacial exciplex to UEML dyes than the counterpart in non-exciplex-based devices ( Wu et al., 2019 ; Wang et al., 2019d ; Sheng et al., 2020 ). After understanding the luminescence mechanism of monochromatic OLEDs based on Donor/UEML/Acceptor structure, in 2020, Ma et al.…”

Recent advances in thermally activated delayed fluorescence for white OLEDs applications

“…The RISC process can accomplish efficiently through smaller ΔE ST . Owing to the preponderances of low turnon voltage and higher power efficiency, there are more and more reports on TADF exciplex-based WOLEDs recently [125][126][127][128][129][130][131][132].…”

High‐Efficiency Nondoped White Organic Light‐Emitting Diodes Based on All‐Exciplex Emission

“…In response to these challenges, Tong et al inserted an ultrathin layer of complementary emitters into blue exciplex to simplify the fabrication process. [ 17–20 ] Ying et al realized a WOLED with a maximum EQE of 21.3% by integrating an interfacial exciplex with multiple ultrathin phosphorescent emissive layers. [ 17 ] Feng et al incorporated an ultrathin yellow fluorescent emissive layer (0.3 nm) into a bilayer blue exciplex system to obtain a WOLED with a maximum current efficiency of 27.2 cd A −1 .…”

“…[ 19 ] Wang et al introduced an ultrathin orange–red phosphorescent emitting layer (0.1 nm) to a blue device with a bilayer interface exciplex structure to obtain a WOLED with a maximum EQE of 20.0%. [ 20 ] All the devices mentioned were structured by combining the emissions of exciplexes and traditional fluorescent or phosphorescent emitters. However, the adoption of all‐exciplex instead of fluorescence–phosphorescence hybrid emitters is more beneficial for obtaining high‐efficiency devices without heavy metal atoms by harvesting both triplets and singlets via RISC and improving the color rendering index (CRI) of devices due to their broader emission spectra.…”