Simple-Structured OLEDs Incorporating Undoped Phosphorescent Emitters Within Non-Exciplex Forming Interfaces: Towards Ultraslow Efficiency Roll-Off and Low Driving Voltage for Indoor R/G/B Illumination

Abstract

To meet the requirement of indoor R/G/B monochrome illumination a simplified OLEDs structure and fabrication process must occur. Herein, a design philosophy of low efficiency roll-off and simple-structure OLEDs incorporating R/G/B phosphorescent ultrathin non-doped emissive layers (EMLs) within non-exciplex forming interfaces a luminescent system by a direct charge trapping mechanism has been reported, which uses bis(2-methyldibenzo[f,h]-quinoxaline)(acetylacetonate)iridium(III) (MDQ)2Ir(acac), bis(3-phenylpyridin-e)iridium(III) (Ir(ppy)3), and bis(3,5-difluoro-2 -(2-pyridyl)phenyl-(2-carboxypyridyl) iridiumII) (Firpic) as R/G/B luminescent dyes, respectively. Although the recombination zone is narrow in the designed OLEDs, the efficiency roll-off of the designed OLEDs are unexpectedly slow, due to stable charge trapping of the emitters and are refrained from concentration quenching in relatively low current density, but the luminance meets the requirement of indoor lighting. With a low threshold voltage of 2.9/2.9/3.5 V, the designed R/G/B phosphorescent OLEDs show an efficiency roll-off as low as 7.6/3.2/4.3% for indoor luminance from 10 cd/m2 to 1,000 cd/m2, respectively. The perspective of R/G/B luminescent dyes on luminous efficiency, chromaticity coordinate drifts, efficiency roll-off, and direct charge trapping has been thoroughly studied. Therefore, our research may help to further develop ideal indoor lighting using a simplified undoped R/G/B OLEDs structure with simultaneous ultraslow efficiency roll-off, low threshold voltage, simplified fabrication process, low reagent consumption, and cost.

Brominated B1-Polycyclic Aromatic Hydrocarbons for the Synthesis of Deep-Red to Near-Infrared Delayed Fluorescence Emitters

“…This is tentatively assigned to PXZ adopting a different conformation in PMMA, which has been previously observed . We then investigated the photophysical behavior of the emitters in 4,4′-bis­( N -carbazolyl)-1,1′-biphenyl (CBP) that has a high triplet energy (2.55 eV) . Compounds 4–6 emit at 623, 682, and 738 nm (Figure b), respectively, with Φ PL values of 39.0%, 6.2%, and 2.8%, respectively (Table ).…”

“…15 We then investigated the photophysical behavior of the emitters in 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP) that has a high triplet energy (2.55 eV). 16 Compounds 4−6 emit at 623, 682, and 738 nm (Figure 4b), respectively, with Φ PL values of 39.0%, 6.2%, and 2.8%, respectively (Table 4c) biexponential decay kinetics consisting of a nanosecond prompt component and a microsecond delayed component (Table 1). The delayed emission tended to increase with temperature, which is consistent with TADF for these three compounds.…”

Recent Progress in Flexible and Wearable All Organic Photoplethysmography Sensors for SpO2 Monitoring

“…Furthermore, the low turn‐on voltage of OLEDs is affected by several factors including the choice of organic materials, energy level alignment, doping, carrier mobility, contact resistances, injection/ blocking interlayers, electrode materials, structure and configuration of the OLED layers stacking and device engineering. [ 132 , 133 , 134 , 135 , 136 , 137 ] Further, active and inter‐layer materials for OLEDs and OPD consist of either solution‐processed polymers or vacuum‐evaporated small molecules. These materials when solution‐coated or vacuum coated under inert conditions will exhibit high charge carrier mobility due to minimum defect states and traps and improves efficiency.…”

Understanding the Structure and Energy Transfer Process of Undoped Ultrathin Emitting Nanolayers Within Interface Exciplexes

“…( Tan et al, 2021 ). Sandwiching the UEML between the exciplex interface of the hole transporting layer (HTL) and electron transport layer (ETL) not only realizes high luminous efficiency due to improved carrier injection and promoted exciton harvesting, ( Xu et al, 2017b ) but also restrains efficiency roll-off, ( Yao et al, 2019 ; Zhang et al, 2021a ; Xu et al, 2021c ) and even extends the working lifetime, owing to good exciton management. ( Li and Liao, 2019 ; Wei et al, 2020 ; Zhang et al, 2020 ; Zhang et al, 2021b ).…”