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"Hot exciton" molecules that allow the transition of excitons from a high‐lying triplet state (Tn, n≥ 2) to singlet states (Sm, m≥1) by a reverse intersystem crossing (hRISC) process have become an effective strategy to achieve high efficiency fluorescence organic light emitting diodes (OLEDs). However, the understanding of the dynamic behavior of the "hot exciton" process is still very lacking. Herein, the exciton dynamics of an aggregation‐induced emission (AIE) molecule TPA‐An‐mPhCz with the "hot exciton" property are deeply investigated, and the proportion between hRISC and internal inversion (IC) of excitons on Tn is successfully quantified by in situ transient electroluminescent measurements and theoretical calculation. It is found that the IC process increases severe energy loss of Tn excitons. By introducing a triplet–triplet annihilation up‐conversion layer in the emissive layer to efficiently recapture the IC excitons and further doping a blue fluorescent emitter in the TPA‐An‐mPhCz layer to achieve high photoluminescence quantum yield (PLQY), the resulting OLED achieves a maximum external quantum efficiency of 12.5% with negligible efficiency roll‐off. More impressively, the operational lifetime LT75 (lifetime to 75% of the initial luminance) of the device with efficient triplets utilization performs a remarkable 116 h under 1000 cd m−2. This work provides the fundamentals for the design of hot exciton materials with efficient exciton utilization to develop efficient blue fluorescence OLEDs. [ABSTRACT FROM AUTHOR]

Aggregation‐induced emission (AIE) materials are attractive for the fabrication of high‐efficiency organic light‐emitting diodes (OLEDs) owing to the "hot exciton" process by reverse intersystem crossing (hRISC) and high photoluminescence quantum yields (PLQY). However, the internal conversion (IC) from the high‐lying triplet excitation states (Tn, n≥2) to the lower excited triplet state (Tn‐1) is inevitable, resulting in severe exciton losses. Herein, an effective device structure is designed that reuses the lost triplet excitons caused by IC and realizes the breakthrough in the efficiency of blue fluorescence OLEDs based on AIE molecule as an emitter. The maximum external quantum efficiency reached as high as 14.8% and is kept at 14.4% at the luminance of 1000 cd m−2. In the designed device, a triplet–triplet annihilation (TTA) up‐conversion material 1‐[2,5‐dimethyl‐4‐(1‐pyrenyl)phenyl]pyrene (DMPPP) is introduced into the AIE emitter as a triplet sensitizer to receive the lost triplet excitons, and a thin TTA up‐conversion layer 9‐[4‐(10‐phenyl‐9‐anthryl)phenyl]‐9H‐carbazole (CzPA) is introduced in the middle of the doped layer to form the emissive layer (EML). It is found that the hRISC process of iTPB‐2AC greatly enhances the utilization efficiency of TTA intermediate state ([TT]*) excitons on CzPA to iTPB‐2AC so that the utilization of the lost excitons is maximized. This work establishes physical insights into the AIE emission materials and device fabrication of high‐efficiency blue fluorescence OLEDs. [ABSTRACT FROM AUTHOR]

The operational lifetime of blue organic light‐emitting diodes (OLEDs) is still insufficient for practical applications in lighting and display. One type of blue organic emitting materials with hybridized local and charge‐transfer (HLCT) process are beneficial in achieving high‐efficiency OLEDs through "hot exciton" channel by harnessing high‐lying triplet (Tn) excitons. However, the operational lifetime of the resulting blue OLEDs is rarely studied and understood. In this article, the aging properties of blue fluorescent OLEDs based on an HLCT material (2‐(4‐(10‐(3‐(9H‐carbazol‐9‐yl)phenyl)anthracen‐9‐yl)phenyl)‐1‐phenyl‐1H‐phenanthro[9,10‐d]imidazole) (PAC) are systematically investigated by exciton dynamics calculation and transient EL experiments. It is experimentally and theoretically revealed that whether the reverse intersystem crossing (hRISC) process from high‐lying excited triplet to singlet in HLCT materials is completely effective determines the device degradation. A fluorescent emitter is doped into PAC host to accelerate the hRISC process, thus enhancing device operational lifetime to reach T75 = 110 ± 2 h (time to 75% of initial luminance) under 1000 cd m−2. This work provides inspirations to investigate the stability of blue fluorescent OLEDs based on HCLT materials and further enhance the operational lifetime. [ABSTRACT FROM AUTHOR]

Aggregation‐induced emission (AIE) and hybridized local and charge‐transfer (HLCT) materials are two kinds of promising electroluminescence systems for the fabrication of high‐efficiency organic light‐emitting diodes (OLEDs) by harnessing "hot excitons" at the high‐lying triplet exciton states (Tn, n ≥ 2). Nonetheless, the efficiency of the resulting OLEDs did not meet expectations due to the possible loss of Tn→Tn−1. Herein, experimental results and theoretical calculations demonstrate the "hot exciton" process between the high‐lying triplet state T3 and the lowest excited singlet state S1 in an AIE material 4⁗‐(diphenylamino)‐2″,5″‐diphenyl‐[1,1″:4′,1″:4″,1′″:4′″,1⁗‐quinquephenyl]‐4‐carbonitrile (TPB‐PAPC) and it is found that the Förster resonance energy transfer (FRET) between two molecules can facilitate the "hot exciton" process and inhibit the T3→T2 loss by doping a blue fluorescent emitter in TPB‐PAPC. Finally, the doped TPB‐PAPC blue OLEDs achieve a maximum external quantum efficiency (EQEmax) of 9.0% with a small efficiency roll‐off. Furthermore, doping the blue fluorescent emitter in a HLCT material 2‐(4‐(10‐(3‐(9H‐carbazol‐9‐yl)phenyl)anthracen‐9‐yl)phenyl)‐1‐phenyl‐1H‐phenanthro[9,10‐d] imidazole (PAC) is used as the emission layer, and the resulting blue OLEDs exhibit an EQEmax of 17.4%, realizing the efficiency breakthrough of blue fluorescence OLEDs. This work establishes a physical insight in the design of high‐performance "hot exciton" molecules and the fabrication of high‐performance blue fluorescence OLEDs. [ABSTRACT FROM AUTHOR]

A novel approach was used in this paper to achieving high resolution of organic light emitting diode (OLED) display by ink‐jet printing (IJP) method. In our work, a structure of line bank with two layers was utilized, in which the bottom and top layers were designed for pixel definition and ink restriction, respectively. As a result, the resolution of our OLED display reached 537 pixels per inch (PPI). Besides the structure, the interface factors of bank materials choice which affect the improvement of resolution was discussed. [ABSTRACT FROM AUTHOR]

Quantum dot display with blue light excitation has attracted a lot of attention recently. In this work, rigid 13.6 inch 1920×1080 FHD full color active matrix quantum dot OLED display (QDOLED) on glass substrate and another evolutional flexible Quantum dot Filter On Electroluminescence display (QFOE) on polyimide (PI) substrate were fabricated with different device configuration. Cd‐free InP QD was introduced into photo‐curable resin and patterned by inkjet‐printing or photolithography process as the color conversion material (CCM). The 2‐stack blue OLED (B‐OLED) device designed under the balance of efficiency and uniformity was employed to excite QD pixel patterns by active matrix driving of coplanar oxide thin‐film transistor (TFT) backplane. The display performances of wide viewing angle, high color purity and excellent contrast ratio are preserved after the flexible process integration into QFOE to show more application potentials in near future. [ABSTRACT FROM AUTHOR]

Phosphorescent organic light‐emitting diodes (PhOLEDs) using exciplexes as host have achieved unprecedented breakthrough. The energy transfer process between host and guest is the popular way to effectively utilize excitons in this kind of devices. Actually, the intermolecular spin–orbital coupling (ISOC) interaction between the heavy‐atom phosphorescent molecule and exciplex also plays an important role in exciton utilization, thus device performance, but this role is always ignored. Here, the synergistic effects of energy transfer and ISOC interaction on device efficiency are clearly demonstrated in exciplex‐based PhOLEDs by magneto‐electroluminescence (MEL) measurements. It can be seen that the MEL line shape at high field component is significantly wider due to the ISOC effect inducing the accelerated transition process between singlet and triplet states of exciplex host. In this case, the energy transfer process from exciplex host to phosphorescent molecule is more efficient, which is confirmed by the different line widths of MELs. Ultimately, a high‐efficiency exciplex‐based green PhOLED with the maximum external quantum efficiency of 23% is obtained at a low phosphorescent doping concentration of 2 wt%. [ABSTRACT FROM AUTHOR]

Aggregation‐induced emission (AIE) materials are highly attractive because of their excellent properties of high efficiency emission in nondoped organic light‐emitting diodes (OLEDs). Therefore, a deep understanding of the working mechanisms, further improving the electroluminescence (EL) efficiency of the resulting AIE‐based OLEDs, is necessary. Herein, the conversion process from higher energy triplet state (T2) to the lowest singlet state (SS1) is found in OLEDs based on a blue AIE material, 4′‐(4‐(diphenylamino)phenyl)‐5′‐phenyl‐[1,1′:2′,1′′‐terphenyl]‐4‐carbonitrile (TPB‐AC), obviously relating to the device efficiency, by magneto‐EL (MEL) measurements. A special line shape with rise at low field and reduction at high field is observed. The phenomenon is further clarified by theoretical calculations, temperature‐dependent MELs, and transient photoluminescence emission properties. On the basis of the T2‐S1 conversion process, the EL performances of the blue OLEDs based on TPB‐AC are further enhanced by introducing a phosphorescence doping emitter in the emitting layer, which effectively regulates the excitons on TPB‐AC molecules. The maximum external quantum efficiency (EQE) reaches 7.93% and the EQE keeps 7.57% at the luminance of 1000 cd m−2. This work establishes a physical insight for designing high‐performance AIE materials and devices in the future. [ABSTRACT FROM AUTHOR]

High efficiency color-tunable organic light-emitting diodes (CT-OLEDs) have been demonstrated by combining non-doped ultra-thin red and green phosphorescent emitters with a blue phosphorescence-doped exciplex system. The resultant devices deliver a sunlight-style emission with a wide correlated color-temperature span from 2143 to 7563 K and achieve the maximum current efficiency, the power efficiency, and the external quantum efficiency of 34.4 cd A−1, 39.5 lm W−1, and 18.6%, respectively, without any out-coupling enhancements. Furthermore, the CT-OLEDs exhibit low efficiency roll-off that the external quantum efficiencies still remain 18.5% and 17.1% even at 1000 and 5000 cd m−2, respectively, which are more efficient than those of state-of-the-art CT-OLEDs. [ABSTRACT FROM AUTHOR]

Abstract: The highly efficient charge generation and transport is realized by simply stacking several 1,4,5,8,9,11‐hexa‐azatriphenylene hexacarbonitrile (HAT‐CN)/4,4′,4″‐tris(N‐3‐methylphenyl‐N‐phenylamino) triph‐enylamine (m‐MTDATA) organic heterojunctions in series. Mechanism analysis confirms that the highly effective charge transport property benefits from the efficient charge generation and recombination processes at the HAT‐CN/m‐MTDATA interfaces. It is found that the efficient multialternating organic heterojunctions can be used not only as hole and electron transporters to supply large charge injection, but also as excellent charge generation layer (CGL) to fabricate high‐performance tandem organic light‐emitting diodes (OLEDs). The resulting red phosphorescent OLEDs by simultaneously using the multialternating organic heterojunctions as hole and electron transporters realize the power efficiency (PE) of 36.7 lm W−1, current efficiency (CE) of 28.0 cd A−1, and external quantum efficiency (EQE) of 15.4%, whereas the PE, CE, and EQE, respectively, reach 37.1 lm W−1, 56.0 cd A−1, and 31.8% when simultaneously using the multialternating organic heterojunctions as hole and electron transporters and CGL to fabricate tandem red phosphorescent OLEDs, indicating the validity of the multialternating organic heterojunctions as the charge generator and transporters. The results provide us a totally new way of fabricating high‐performance OLEDs. [ABSTRACT FROM AUTHOR]

White organic light‐emitting diodes (WOLEDs) are one of the most cogent candidates for environment friendly and healthy solid‐state lighting due to many unique merits. Here, a strategic design of exciplex hosts is applied to simultaneously realize the superior color stability, high color rendering index (CRI), high efficiency, and low efficiency roll‐off properties of WOLEDs. The resulting WOLEDs emit the forward‐viewing maximum power efficiency (PE) of 59.9 lm W−1, and the PE still remains 45.3 and 31.9 lm W−1 at 1000 and 5000 cd m−2, respectively, exhibiting extremely low efficiency roll‐off. More remarkably, the devices also show high CRI over 80 and extremely stable spectral emission in the luminance ranges from 1000 to 15 000 cd m−2. The excellent performances indicate the validity of the structure design and provide a new route for the development of high‐performance WOLEDs. [ABSTRACT FROM AUTHOR]

OLEDs with high efficiency and low roll‐off are urgently needed to meet the constantly increasing commercial demands for white organic light‐emitting diodes (WOLEDs) in lighting industry applications. To enhance efficiency and decrease WOLED roll‐off, complicated doping technologies are employed, which result in an additional increase in costs. Herein, a deep‐blue‐light molecule (3TPA‐CN) with aggregation‐induced emission (AIE) is introduced as blue emitter and phosphor host to fabricate WOLEDs. By optimizing the emission zones, high efficiency and low roll‐off hybrid WOLEDs are achieved. The maximum forward‐viewing power and external quantum efficiencies reach 86.7 lm W−1 and 22.3%, and remain 59.2 lm W−1 and 19.6% at a luminance of 1000 cd m−2, fully exhibiting the prospect of AIE molecules as a promising electroluminescence material for the fabrication of high‐performance WOLEDs. [ABSTRACT FROM AUTHOR]

It is still challenging to achieve blue OLEDs with sufficient color purity, lifetime and efficiency for applications. Thermally activated delayed fluorescence (TADF) materials become the most promising. However, the internal mechanism of the efficiency roll-off and long-term stability degradation still needs deep research. In this work, the energy transfer and exciton quenching processes in TADF-based blue OLEDs were analyzed under steady-state conditions and their relative contributions to efficiency roll-off were quantified. Furthermore, the degradation mechanism in the TADF-based blue OLEDs was investigated both theoretically and experimentally by a comprehensive exciton quenching model. It was demonstrated that suppressing the triplet–polaron annihilation processes and reducing the accumulation of triplet excitons through reasonable energy transfer can decrease the effect of exciton quenching, thereby significantly reduce the efficiency roll-off and improve device lifetime. It can be seen that the external quantum efficiency (EQE) of the resulting blue OLEDs was enhanced to 30.3 % with CIE coordinates of (0.16, 0.25) and kept 20.9 % at the luminance of 1000 cd/m2. More importantly, the device lifetime was also significantly enhanced, which is over three times longer than that of the unoptimized devices due to the suppress of triplet-polaron annihilation and triplet accumulation. Reducing the accumulation of triplet excitons through reasonable energy transfer can suppress the triplet–polaron annihilation processes, and significantly reduce the efficiency roll-off and improve device lifetime. [Display omitted] • The energy transfer, exciton quenching processes and degradation mechanism in TADF-based blue OLEDs were analyzed. • The degradation mechanism in the TADF-based blue OLEDs was investigated both theoretically and experimentally by a comprehensive exciton quenching model. • The EQE of the OLEDs was enhanced to 30.3 %. • The lifetime of the OLEDs was enhanced due to the suppress of triplet-polaron annihilation. [ABSTRACT FROM AUTHOR]

The charge generation mechanism of organic heterojunction (OHJ) consisted of 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile (HAT-CN) and different hole transporting materials (HTMs) are studied systematically by current-voltage (I–V) and capacitance-voltage measurements. The analysis of I–V characteristics of the devices based on OHJs at forward and reverse voltages by comparing the thickness of HTM layers finds that a forward and reverse symmetrical I–V curve is observed at thin HTM layers and the forward current becomes larger than the reverse current with the increase of HTM thickness, fully illustrating the effectiveness of OHJ charge generation. Moreover, the I–V characteristics at different temperatures indicate that the efficient charge generation is originated from electron tunneling rather than diffusion. And the C–V and capacitance-frequency (C–F)characteristics further illustrate the highly efficient charge generation ability of OHJs so that the charge density is as high as 4.5 × 1017 cm−3, guaranteeing the high conductivity of OHJs, which is very beneficial to developing highly efficient OLEDs using OHJs as charge injector and generator. The mechanism of charge generation in orgainc heterojunctions have been systematically studied via the analysis of I–V and C–V characteristics, which not only reveals that the highly efficient charge generation process is originated from the electron tunneling rather than the diffusion, but also exhibited the high charge density (4.5 × 1017 cm−3), ensure the high conductivity of OHJs. Image 1 • The charge generation process of OHJ is studied via the analysis of I–V and C–V characteristics. • The electron tunneling model of charge generation process is revealed. • The free charge density of OHJ is calculated as high as 4.5 × 1017 cm−3. [ABSTRACT FROM AUTHOR]

White organic light-emitting diodes (WOLEDs) with ultra-thin emitting layers have shown considerable potential in solid-state lighting fields due to the simplified structures. However, such WOLEDs with high efficiency, high color rendering index (CRI) and stable spectral emission are still facing challenges. In this paper, we demonstrated a high efficiency and high CRI phosphorescent WOLED by strategically adjusting the positions of red, green and blue phosphorescent ultra-thin layers in exciplex emitter. By investigating the processes of energy transfer and utilization of triplet excitons, a high efficiency, high CRI and stable spectrum emission warm WOLED was successfully fabricated. The maximum external quantum efficiency (EQE), power efficiency (PE) and current efficiency (CE) reached 26.1%, 50 lm W−1,and 40 cd A−1, respectively, and the CRI was as high as 80 in the luminance range from 1000 cd m−2 to 30000 cd m−2 with stable emission spectra, exhibiting superior comprehensive EL performances. This work also indicates the potential of undoped ultra-thin layer structures to fabricate high performance WOLEDs for lighting applications. High efficiency and color quality White Organic Light-emitting Diodes have been demonstrated by strategically adjusting the positions of red, green and blue phosphorescent ultrathin layers in exciplex emitter and adding another channel to fully utilized CT state excitons. Image 1 • A doping-free white organic light-emitting diode can sufficiently simplify the device's structure and lower the cost. • The efficiency has been improved by strategically establishing another channel for blue emission to fully use excitons. • A full-phosphorescent WOLED with high efficiency, high color quality has been achieved based on exciplex. [ABSTRACT FROM AUTHOR]

Fluorescent organic light-emitting diodes (OLEDs) have aroused a lot of attention due to the advantages of lost cost, good operational stability and low efficiency roll-off. However, how to realize high efficiency and long lifetime fluorescent OLEDs simultaneously is still a huge challenge. The use of exciplex and thermally activated delayed fluorescence (TADF) materials as sensitizers for conventional fluorescent emitters is a promising route to improve the efficiency and operational stability of fluorescent OLEDs. Herein, we demonstrate a novel strategy by using a TADF material as sensitizer in exciplex host to realize high efficiency and long lifetime fluorescent OLEDs. The key in our design is the further formation of additional exciplex between TADF sensitizer and electron-acceptor, thus three RISC processes to efficiently convert triplet excitons into singlet excitons by cascaded energy transfer processes. Based on this design strategy, the resulting fluorescent OLEDs achieve the maximum current efficiency (CE), power efficiency (PE) and external quantum efficiency (EQE) of 22.6 cd A−1, 29.5 lm W−1 and 13.0%, and the operational lifetime LT 50 (decay to 50% of the initial luminance of 1000 cd m−2) reaches 415 h, which are significantly higher than those based on the conventional sensitized methods, fully demonstrating the effectiveness of our design concept to realize higher efficiency and longer lifetime fluorescent OLEDs. The novel strategy of utilizing triplet excitons efficiently based on cascaded energy transfer processes to realize high efficiency and long lifetime OLEDs. Image 1 • An additional exciplex is formed between TADF sensitizer and electron-acceptor of exciplex host. • Three RISC processes in EML utilize triplet excitons efficiently by cascaded energy transfer processes. • The resulting fluorescent OLEDs show the higher efficiencies and longer operational lifetime. [ABSTRACT FROM AUTHOR]

An efficient planar organic heterojunction (OHJ) consisted of 1,4,5,8,9,11-hexaazatriphenylene- hexacarbonitrile (HAT-CN)/1,1-bis [(di-4-tolyamino)phenyl)]cyclohexane (TAPC) is employed simultaneously as both charge generation layer (CGL) and charge injectors to fabricate high efficiency and long lifetime tandem organic light-emitting diodes (OLEDs). It can be seen that compared with conventional tandem OLEDs, the tandem OLEDs utilizing OHJ as both CGL and charge injectors significantly improved not only the current and quantum efficiencies, more importantly, but also the power efficiency and stability. The maximum efficiencies were as high as 42.0%, 159.5 cd A-1 and 92.7 lm W-1, and the lifetime reached 1350 h, which are more higher than the efficiencies of 34.3% 130.2 cd A-1 and 75.0 lm W-1 and the lifetime of 859 h of conventional tandem OLEDs. The more balanced charge generation and injection due to the simultaneous utilization of OHJ as CGL and charge injectors contributed to the significant improvement in the performance of resulting tandem OLEDs. These results fully indicate the validity of OHJ as CGL and charge injectors, and also provide a new route for the development of high performance OLEDs. High efficiency and long lifetime tandem OLEDs that utilize HAT-CN/TAPC (OHJs) as both charge generation layer (CGL) and charge injectors are fabricated, achieving a novel charge injection way, which is not only different from the injection via electrodes in traditional OLEDs, but also is benefical to realize the more balanced charge injection. Image 1 • Organic heterojunction HAT-CN/TAPC simultaneously as both charge generation layer and charge injectors is proposed. • High efficiency and long lifetime tandem OLEDs based HAT-CN/TAPC are successfully fabricated. • The more balanced charge generation and injection are realized in studied OLEDs. [ABSTRACT FROM AUTHOR]