Fluorescent White Organic Light-emitting Diodes Research Articles

Highly efficient fluorescent and hybrid white organic light-emitting diodes based on a bimolecular excited system: publisher's note.

This publisher's note contains a correction to Opt. Lett.48, 5771 (2023)10.1364/OL.506371.

Highly efficient fluorescent and hybrid white organic light-emitting diodes based on a bimolecular excited system.

A bimolecular excited system is considered as a promising candidate for developing white organic light-emitting diodes (WOLEDs) with reduced phosphorescent components. However, for actualizing high-performance WOLED, little attention has been paid to electromers compared to exciplexes. Herein, we construct the bimolecular excited system to prepare fluorescent WOLEDs by combining the electromer emission with the exciplex emission, achieving a maximum power efficiency of 11.8 lm/W with a color rendering index (CRI) of over 80. Furthermore, phosphorescent dopants are doped into an exciplex host to construct hybrid WOLEDs. The fabricated complementary-color and three-color devices achieve maximum efficiencies of 55.3 cd/A (46.8 lm/W) and 34.1 cd/A (26.8 lm/W), respectively. The spectral coverages of WOLEDs are broadened by the bimolecular excited system, and CRIs are further improved at high luminance. Our strategy may bring light to the future development of highly efficient WOLEDs with economy and sustainability.

High-efficiency all fluorescence white OLEDs with high color rendering index by manipulating excitons in co-host recombination layers.

All fluorescence white organic light-emitting diodes (WOLEDs) based on thermally activated delayed fluorescence (TADF) emitters are an attractive route to realize highly efficient and high color quality white light sources. However, harvesting triplet excitons in these devices remains a formidable challenge, particularly for WOLEDs involving conventional fluorescent emitters. Herein, we report a universal design strategy based on a co-host system and a cascaded exciton transfer configuration. The co-host system furnishes a broad and charge-balanced exciton generation zone, which simultaneously endows the devices with low efficiency roll-off and good color stability. A yellow TADF layer is put forward as an intermediate sensitizer layer between the blue TADF light-emitting layer (EML) and the red fluorescence EML, which not only constructs an efficient cascaded Förster energy transfer route but also blocks the triplet exciton loss channel through Dexter energy transfer. With the proposed design strategy, three-color all fluorescence WOLEDs reach a maximum external quantum efficiency (EQE) of 22.4% with a remarkable color rendering index (CRI) of 92 and CIE coordinates of (0.37, 0.40). Detailed optical simulation confirms the high exciton utilization efficiency. Finally, by introducing an efficient blue emitter 5Cz-TRZ, a maximum EQE of 30.1% is achieved with CIE coordinates of (0.42, 0.42) and a CRI of 84 at 1000 cd m-2. These outstanding results demonstrate the great potential of all fluorescence WOLEDs in solid-state lighting and display panels.

High-efficiency hyperfluorescent white light-emitting diodes based on high-concentration-doped TADF sensitizer matrices via spatial and energy gap effects.

Despite the success of monochromatic hyperfluorescent (HF) organic light-emitting diodes (OLEDs), high-efficiency HF white OLEDs (WOLEDs) are still a big challenge. Herein, we demonstrate HF WOLEDs with state-of-the-art efficiencies, featuring a quasi-bilayer emissive layer (EML) composed of an ultrathin (0.1 nm) blue fluorescence (FL) emitter (TBPe) layer and a layer of thermally activated delayed fluorescence (TADF) sensitizer matrix heavily doped with a yellow FL emitter (TBRb, 3%). Based on an asymmetric high-energy-gap TADF sensitizer host (PhCzSPOTz), such an “ultrathin blue emitting layer (UTBL)” strategy endowed the HF WOLEDs with a record power efficiency of ∼80 lm W−1, approaching the level of fluorescent tubes. Transient photoluminescence (PL) and electroluminescence (EL) kinetics demonstrate that the spatial separation of TBPe from the TADF sensitizer and TBRb, and the large energy gap between the latter two effectively suppress triplet leakage, in addition to suppressing triplet diffusion in the PhCzSPOTz matrix with anisotropic intermolecular interactions. These results provide a new insight into the exciton allocation process in HF white light-emitting systems.

Direct evidence of dopant-dopant synergism in efficient single-emissive-layer white thermally activated delayed fluorescence

Major efforts were previously devoted to incorporate high-efficiency blue dopants into thermally activated delayed fluorescence (TADF) white organic light-emitting diodes (WOLED). Herein, we demonstrate that the synergism of blue and yellow TADF dopants in terms of efficient exciton allocation and quenching suppression are more crucial for achieving high-performance single-emissive-layer TADF WOLEDs. Based on three blue TADF emitters xDMACPO with markedly stronger host characteristics but relatively lower photoluminescence (PL) quantum yields than a conventional blue TADF emitter DMAC-DPS, transient PL and electroluminescence (EL) analyses give the direct evidences that in contrast to serious emission quenching of DMAC-DPS by co-doping a yellow emitter 4CzTPNBu, 4CzTPNBu hardly reduces TADF performance of xDMACPO, but even improved EL efficiencies of xDMACPO through complementing with each other in exciton harvesting. xDMACPO in turn mitigate emission quenching of 4CzTPNBu, among which TDMACPO most compatible with 4CzTPNBu dramatically elevates the efficiencies of the TADF WOLED by one third.

A phosphorated spirobi[thioxanthene] host matrix enables high-efficiency simple white thermally activated delayed fluorescence diodes

Host matrix is crucial for optimizing exciton allocation in all Thermally activated delayed fluorescence (TADF) white Organic light-emitting diodes (OLED). However, only few spiro hosts are competent since unbalanced steric and electronic effects. Herein, a new spiro core 9,9′-spirobi[thioxanthene] (ST) based host STDPO is reported, whose two peripheral diphenylphosphine oxide (DPPO) groups are incorporated to construct tridimensional steric hindrance and Intermolecular hydrogen bond (IHB) network. As consequence, STDPO achieves the high enough first triplet (T1) energy level of 2.93 eV and favorable electron mobility (µe) by the level of 10−5 cm2 V−1 s−1. Simultaneously, the well-modulated intermolecular interactions in STDPO matrix give rise to the synergistic effect of blue and yellow TADF dopants in exciton utilization. The increased rate constants and efficiencies of radiative transitions and reduced nonradiative rate constants render a photoluminescence quantum yield as high as 90% and 100% exciton utilization efficiency of dually doped white TADF film. STDPO further endowed its single-emissive-layer TADF WOLEDs with the record ηPE of 71.8 lm W−1 achieved by spiro hosts.

Vibratile Dihydrophenazines with Controllable Luminescence Enabled by Precise Regulation of π-Conjugated Wings

Vibratile Dihydrophenazines with Controllable Luminescence Enabled by Precise Regulation of π-Conjugated Wings

Combining complementary emissions of hole- and electron-transport layers for ultra-simple white organic light-emitting diodes achieving high device performance

In this work, we proposed a novel and ultra-simple all fluorescent di-chromatic white organic light-emitting diodes (WOLEDs) containing only three non-doped organic layers, which are yellow emitting hole-transport layer, blue emitting electron-transport layer, and charge adjusting layer inserted between hole- and electron-transport layers. White light emission can be realized by simultaneously combining complementary emissions of hole- and electron-transport layers. Based on this structure, a series of all fluorescent di-chromatic WOLEDs were developed, and it was demonstrated the emission spectra could be easily improved by simply changing the thickness of charge adjusting layer. As a consequence, the optimized di-chromatic WOLED achieves a high color rendering index (CRI) of 86, to the best of our knowledge, which is among the highest CRI for such simple structures reported in the literatures. And the resulting device also exhibits high color stability with a slight change of (0.00, −0.01) for CIE coordinates at a wide luminance range from 1011 cd/m2 to 9310 cd/m2. Moreover, efficiency roll-off is rarely observed for target device before luminance reaching 10,000 cd/m2. Such high device performance can be attributed to i) absolutely complementary emissions for hole- and electron-transport layers; ii) a balanced excitons distribution on two transport layers; and iii) a wide carriers recombination zone extending throughout both transport layers. We believe this work will provide a guide to develop simplified but high performance WOLEDs.

Ladder-like energy-relaying exciplex enables 100% internal quantum efficiency of white TADF-based diodes in a single emissive layer

Development of white organic light-emitting diodes based on purely thermally activated delayed fluorescence with a single-emissive-layer configuration has been a formidable challenge. Here, we report the rational design of a donor-acceptor energy-relaying exciplex and its utility in fabricating single-emissive-layer, thermally activated delayed fluorescence-based white organic light-emitting diodes that exhibit 100% internal quantum efficiency, 108.2 lm W−1 power efficiency, and 32.7% external quantum efficiency. This strategy enables thin-film fabrication of an 8 cm × 8 cm thermally activated delayed fluorescence white organic light-emitting diodes (10 inch2) prototype with 82.7 lm W−1 power efficiency and 25.0% external quantum efficiency. Introduction of a phosphine oxide-based acceptor with a steric group to the exciplex limits donor-acceptor triplet coupling, providing dual levels of high-lying and low-lying triplet energy. Transient spectroscopic characterizations confirm that a ladder-like energy relaying occurs from the high-lying triplet level of the exciplex to a blue emitter, then to the low-lying triplet level of the phosphine oxide acceptor, and ultimately to the yellow emitter. Our results demonstrate the broad applicability of energy relaying in multicomponent systems for exciton harvesting, providing opportunities for the development of third-generation white organic light-emitting diode light sources.

High-power-efficiency thermally activated delayed fluorescence white organic light-emitting diodes based on asymmetrical host engineering

Developing thermally activated delayed fluorescence (TADF) white organic light emitting diodes (WOLED) featuring high power efficiencies faces a challenge in balancing carrier transport, energy transfer and quenching suppression. Here, we demonstrate that host matrix is crucial for the modification of optoelectronic process in emissive layers (EML) and the achievement of high power efficiency. Through asymmetrically introducing two or three diphenylphosphine oxide (DPPO) groups, three phosphine oxide (PO) hosts 24DBFDPO , 26DBFDPO and 248DBFTPO were constructed, in which dibenzofuran (DBF) chromophore is embedded by rationally spatial distribution of DPPO groups in 26DBFDPO and 248DBFTPO . Direct steric effect of DPPOs suppresses the host-dopant and dopant-dopant interaction induced quenching and mitigates excessive dopant-dopant energy transfer. Dually-doped white TADF films of 248DBFTPO reveal the improved white color purity with a high quantum yield of ~ 90%. Simultaneously, remote steric and electron-withdrawing effects of DPPOs remedy carrier transport in 248DBFTPO films. Based on a simple trilayer single-EML device structure, 248DBFTPO endowed its full-TADF WOLEDs with the state-of-the-art performance, especially the top-rank power efficiency beyond 70 lm W −1 . This work indicates host engineering can provide a feasible approach to realize the practical application of TADF daily lighting. • Host engineering based Asymmetric phosphine oxide hosts were implemented for white TADF diodes. • Intermolecular interactions in host matrixes are accurately adjusted with spatial asymmetry of phosphine oxide groups. • Carrier mobility of 10 −6 cm 2 V −1 s −1 for neat films and ~ 90% PLQYs of blue and white TADF doped films are achieved. • High power efficiency beyond 70 lm W −1 was realized by a simple trilayer single-emissive-layer TADF WOLED.

High efficiency and long lifetime fluorescent white organic light-emitting diodes by phosphor sensitization to strategically manage singlet and triplet excitons

The positions of the phosphor-sensitized yellow EML from the exciton recombination zone were controlled to strategically utilize singlet and triplet excitons for blue and yellow emissions to realize high-performance fluorescent WOLEDs.

Exciton engineering based on star-shaped blue thermally activated delayed fluorescence emitters for efficient white organic light-emitting diodes

Accurate exciton allocation in thermally activated delayed fluorescence (TADF) white organic light-emitting diodes (OLEDs) was realized to achieve the efficient efficient white emission.

High fluorescence efficiency of dual-wavelength white OLED with NPB emission and triplet annihilation

A high-efficiency fluorescent dual-wavelength white organic light-emitting diode (WOLED) was fabricated with a single emission layer (EML) comprising ITO/MoO3/NPB/Spiro-Pye:DCJTB/Bphen/LiF/Al. OLEDs with a 2 nm-thick MoO3 showed a 6% decrease in the operating voltage and a 14% increase in the external quantum efficiency (EQE). The NPB emission that occurred near the NPB/EML interface was investigated with a carrier blocking layer containing Ir(ppy)3 and Ir(piq)3. Excess electrons in the EML affected the emission of NPB, even at a low voltage of 4 V. The maximum luminescence, current efficiency, and power efficiency of the WOLED were 21,070 cd/m2, 18.09 cd/A, and 8.77 lm/W, respectively. A high EQE of 8.16% was achieved, which exceeded the theoretical limit of 5% for all-fluorescent OLEDs.

Triplet collection for highly efficient single-emitting-layer pure fluorescent WOLED based thermally activated delayed fluorescent host of acridine/sulfone derivative

Abstract Herein, highly efficient single-emitting-layer structure pure fluorescent white organic light-emitting diodes (WOLED) were designed by employing thermally activated delayed fluorescence emitter of mSOAD as host material to sensitize traditional fluorescent dopant of Rubrene and DCJTB, respectively. The WOLED based Rubrene dopant achieve a cool white emission with maximum current efficiency, power efficiency and external quantum efficiency of 33.0 cd/A, 34.5 l m/W and 12.2%, respectively. While a warm white emission with the efficiency of 20.9 cd/A, 20.1 lm/W and 9.0%, respectively, were realized in WOLED based DCJTB dopant. The study to energy level and photoluminescence transient decay lifetime demonstrate the sufficient confinement to charges and excitons, and efficient triplet collection by host triplet exciton reverse intersystem crossing and energy transfer to dopant are the reasons of high device efficiency and stable spectra.

A π-D and π-A Exciplex-Forming Host for High-Efficiency and Long-Lifetime Single-Emissive-Layer Fluorescent White Organic Light-Emitting Diodes.

Exciplex-forming hosts with thermally activated delayed fluorescence (TADF) provide a viable opportunity to unlock the full potential of the yet-to-be improved power efficiencies (PEs) and stabilities of all-fluorescent white organic light-emitting diodes (WOLEDs), but this, however, is hindered by the lack of stable blue exciplexes. Here, an advanced exciplex system is proposed by incorporating bipolar charge-transport π-spacers into both the electron-donor (D) and the electron-accepter (A) to increase their distance for hypsochromic-shifted emission while maintaining the superior transporting ability. By using spirofluorene as the π-spacer, 3,3'-bicarbazole as the D-unit, and 2,4,6-triphenyl-1,3,5-triazine as the A-unit, a π-D and π-A exciplex with sky-blue emission and fast reverse intersystem crossing process is thereof constructed. Combining this exciplex-forming host, a blue TADF-sensitizer, and a yellow conventional fluorescent dopant in a single-emissive-layer, the fabricated warm-white-emissive device simultaneously exhibits a low driving voltage of 3.08 V, an external quantum efficiency of 21.4%, and a remarkable T80 (time to 80% of the initial luminance) of >8200 h at 1000 cd m-2 , accompanied by a new benchmark PE of 69.6 lm W-1 among all-fluorescent WOLEDs.

Symmetrical spirobi[xanthene] based locally asymmetrical phosphine oxide host for low-voltage-driven highly efficient white thermally activated delayed fluorescence diodes

• A spiro host with local asymmetry for blue and white TADF OLED. • Intermolecular interactions are optimized for optoelectronic improvement. • The full-TADF white OLED achieved the state-of-the-art performance. The balance between the electrical performance and quenching suppression is crucial to develop the efficient host materials for full-thermally activated delayed fluorescence (TADF) white organic light-emitting diodes (WOLEDs). In this work, through introducing one bulky diphenylphosphine oxide (DPPO) group at 4 position of each xanthene ring in a symmetrical and orthogonal spirobi[xanthene] (SX) skeleton, 9,9′-spirobi[xanthene]-4,4′-diylbis(diphenylphosphine oxide) ( SXDPO ) was constructed, giving rise to the optimized intermolecular interactions. Besides the high triplet (T 1 ) energy level of 2.94 eV, the highly rigid configuration of SXDPO simultaneously rendered the dramatically suppressed excited-state relaxation and the stable and uniform amorphous phase of its films before and after doping TADF dyes. It was interesting that SXDPO showed the complementary electrical properties to enhance the carrier transportation in the films. Therefore, SXDPO successfully achieved the balance between the electrical performance improvement and the collisional quenching suppression. As the result, SXDPO endowed its complementary TADF WOLEDs with the state-of-the-art performance, e.g. the turn-on voltage as low as 2.8 V and power efficiency beyond 60 lm W −1 , which was one of the best comprehensive results reported so far for full-TADF WOLEDs.

High efficiency and low efficiency roll-off all fluorescent white organic light-emitting diodes based on phosphor sensitization

All fluorescent white organic light-emitting diodes (WOLEDs) have aroused significant interest owing to the advantages of excellent operational stability, low efficiency roll-off and low cost.

High efficiency, low efficiency roll-off and long lifetime fluorescent white organic light-emitting diodes based on strategic management of triplet excitons via triplet–triplet annihilation up-conversion and phosphor sensitization

High performance fluorescent WOLEDs based on strategic management of triplet excitons.

Optimizing energy transfer for highly efficient single-emissive-layer white thermally activated delayed fluorescence organic light-emitting diodes.

Thermally activated delayed fluorescence (TADF) white organic light-emitting diodes (WOLEDs) with simplified structures have great potential for daily lighting applications. However, the complicated energy and charge transfer processes between TADF emitters impede the development of single-layer white TADF systems. Here we demonstrate high-efficiency WOLEDs with single-emissive layers composed of blue and yellow TADF emitters with appropriate steric hindrances and energy gaps, which optimize the energy transfer from blue to yellow dopants for rational exciton allocation. As a consequence, the single-emissive-layer WOLEDs achieve the maximum external quantum efficiency beyond 20% and small roll-offs, which are among the best results of full-TADF WOLEDs.

Nondoped Red Fluorophores with Hybridized Local and Charge-Transfer State for High-Performance Fluorescent White Organic Light-Emitting Diodes.

Two red fluorophores (TPABTPA and TPABCHO) with hybridized local and charge-transfer properties were systematically studied. TPABTPA and TPABCHO enabled nondoped organic light-emitting diodes (OLEDs) with excellent external quantum efficiency (EQE) of 11.1% and 5.0%, respectively, attributed to high exciton utilization efficiency of 82% and 46%, respectively. Furthermore, TPABTPA and TPABCHO were utilized as complementary emitters for a sky-blue thermally activated delayed fluorescence material to fabricate two-color fluorescent white OLEDs (WOLEDs) in a fully nondoped emissive-layer configuration. Furthermore, device performance was optimized through a simple device engineering strategy by sandwiching a suitable interlayer between the emitting layers. As a result, the optimized TPABTPA- and TPABCHO-based WOLEDs successfully achieved high EQEs of 23.0% and 8.6%, respectively, along with a low efficiency roll-off and good spectral stability, due to high exciton utilization efficiency of the emitters and importantly efficient suppression of a nonradiative energy-transfer process.