Highly Efficient, Simplified Monochrome and White Organic Light‐Emitting Devices based on Novel Exciplex Host

Abstract

along with a wide T 1 level, especially for blue phosphorescent OLEDs. [7,8] Recently, exciplex formed by an acceptor and a donor is seen as a promi sing candidate for using as a host in OLEDs because of its plastic transport capability and energy band gap. [9][10][11][12][13][14][15] Moreover, most exciplex systems exhibit thermally activated delayed fluorescence (TADF) process via reverse intersystem crossing (RISC), in which triplet excitons can be upconverted into singlet excitons arisen from their minor singlettriplet energy differences (ΔE ST ). [16][17][18][19] It is found that an efficient TADF host could facili tate the energy transfer mechanism vari ation from the Dexter energy transfer to the Förster energy transfer, giving rise to further enhanced device efficiency. [20][21][22] These advantages encourage the devel opment of the exciplex cohost so that many exciplex cohost systems have been reported to demonstrate highly efficient monochrome and white phosphorescent OLEDs. Chang et al. adopted exciplex cohost to realize red, green, blue phosphores cent OLED provided maximum external quantum efficiencies (EQEs) of 8.8%, 14.1%, and 15.8%. [23] Ma et al. demonstrated blue phosphorescent with efficiency of 47.1 lm W −1 as well as white OLED (WOLED) with high efficiency of 75.3 lm W −1 . [24] However, inferior color qualities and instability of spectra are frequently accompanied in these devices. Highly effective exci plex cohost system that is able to realize good colorpure OLED and superior colorstable WOLED has not been reported yet.In this work, a novel exciplex cohost system constructed by the donor of (N,N′dicarbazolyl3,5benzene) (MCP) and the acceptor of 4,6bis[3,5(dipyrid3yl)phenyl]2phenylpyrimi dine (B4PyPPM) was proposed to fabricate phosphorescent OLEDs with simplified structure. Compared with traditional hostsbased devices, the blue/green/orange/red phosphores cent OLEDs based on the exciplex cohost exhibited stable color purity and higher EQEs of 20.1%, 26.3%, 24.6%, 19.8%, respec tively. By combining with blue and orange phosphor, double emission layer WOLED was realized with maximum efficiency of 73.6 lm W −1 and suppressed efficiency rolloff. Furthermore, extremely minor Commission Internationale de L, Eclairage (CIE) coordinates variation was only (0.008, 0.002) over a large luminance range, which was among the best in exciplex co host WOLEDs. Detail investigation demonstrated the balanced charge transport property of exciplex cohost and multipleThe exciplex co-host system is one of the most promising candidates for developing phosphorescent organic light-emitting diodes (OLEDs) with high performance. However, highly effective exciplex co-host system that is able to realize color-pure monochrome OLED and superior color-stable white OLED simultaneously is rarely reported so far. Herein, a novel exciplex cohost system formed by the donor of (N,N′-dicarbazolyl-3,5-benzene) (MCP) and the acceptor of 4,6-bis[3,5-(dipyrid-3-yl)-phenyl]-2-phenylpyrimidine (B4PyPPM) is constructed successfully to ...

Highly efficient, ultralow turn-on voltage red and white organic light-emitting devices based on a novel exciplex host

“…(3) The exciplex need to have a higher T1 level than phosphorescent dopants to restrain energy transfer from the phosphors to the exciplex. 28,29 According to the PL spectrum (S1=2.258 eV) and ΔE ST (0.022 eV) of the exciplex, T1 can be estimated to be about 2.236 eV, which is obviously lower than FSF4A (2.6 eV) and PO-T2T (3.0 eV). 40 Therefore, the red dye Ir(MDQ) 2 acac (2.0 eV) is used as a dopant to design red PhOLEDs based on the characteristics of a novel exciplex co-host.…”

“…Sheng et al adopted exciplex cohost to achieve red phosphorescent OLEDs with maximum power efficiency of 35.3 lm W -1 and external quantum efficiency of 19.8%. 28 Xu et al reported a red phosphorescent OLED through exciplex cohost system with maximum power efficiency of 31.8 lm W -1 and turnon voltage of 2.24 V. 29 Yao et al realized a red phosphorescent device with a maximum power efficiency of 36.9 lm W -1 and external quantum efficiency of 15.5%. 30 However, despite the remarkable progress in the use exciplex co-hosts in OLEDs, it is still a great challenge to precisely predict the likelihood of electron hole pairs induce exciplex emission and achieve ultra-low turn-on voltage PhOLEDs.…”

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.…”

High efficiency and low operating voltage yellow phosphorescent organic light-emitting diodes with a simple doping-free structure

“…Moreover, owing to small orbital overlap between the excited state and the ground state, most exciplex possess a small DEst (S 1 -T 1 energy splitting), which promotes the energy transfer process changing from Dexter energy transfer to Förster energy transfer in host-guest doping system. 8,[11][12][13][14][15][16][17] For example, Park et al 16 doped bis(2phenylpyridine)(acetylacetonato) iridium(III) (Ir(ppy) 2 acac) into the exciplex co-host formed by 4,4 0 ,4 00 -tri(N-carbazolyl) triphenylamine(TCTA) and bis-4,6-(3,5-di-3-pyridylphenyl)-2methylpyrimidine (B3PYMPM) to achieve green PhOLED with low turn-on voltage of 2.4 V and high external quantum efficiency (EQE) of 29.1% as well as low roll-off. Wang et al 17 employed interfacial exciplex of (N,N 0 -di(naphth-1-yl)-N,N 0diphenyl-benzidine (NPB)/1,3,5 tris[N-(phenyl) benzimidazole]-benzene (TPBi) as co-host to fabricate a red PhOLED showing a high EQE of 17.2% and a low turn-on voltage of 2.6 V simultaneously.…”