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The two blue MR-TADF emitters Me-PABO and Me-PABS were designed and synthesized. The devices employing Me-PABO and Me-PABS as emitters exhibited EQEmax of 20.4% and 23.0%, and CIE of (0.13, 0.09) and (0.12, 0.14), respectively.

Blue emitting CsPb(Br–Cl)3 perovskite nanoparticles (NPs) play an important role in optoelectronic applications.

A high maximum external quantum efficiency of an all-solution-processed quantum dot light-emitting diode is demonstrated to be 28.6% by tailoring the electron injection for balancing the charge injection in a QLED.

Achieving high-efficiency deep blue emitter with CIEy 10% has been a long-standing challenge for traditional fluorescent materials in organic light-emitting diodes (OLEDs). Here, we report the rational design and synthesis of two new deep blue luminogens: 4-(10-(4′-(9H-carbazol-9-yl)-2,5-dimethyl-[1,1′-biphenyl]-4-yl)anthracen-9-yl)benzonitrile (2M-ph-pCzAnBzt) and 4-(10-(4-(9H-carbazol-9-yl)-2,5-dimethylphenyl)anthracen-9-yl)benzonitrile (2M-pCzAnBzt). In particular, 2M-ph-pCzAnBzt produces saturated deep blue emissions in a non-doped electroluminescent device with an exceptionally high EQE of 10.44% and CIEx,y (0.151, 0.057). The unprecedented electroluminescent efficiency is attributed to the combined effects of higher-order reversed intersystem crossing and triplet-triplet up-conversion, which are supported by analysis of theoretical calculation, triplet sensitization experiments, as well as nanosecond transient absorption spectroscopy. This research offers a new approach to resolve the shortage of high efficiency deep blue fluorescent emitters.

A room-temperature technique with all-nonpolar-solvent, which circumvents the sensitivity of ionic perovskite to polar solvent, has become attractive for the synthesis of metal halide perovskite nanocrystals (PNCs). However, the lack of understanding of the inner mechanism, especially for the state of the precursor and the crystallization process of the PNCs, hinders further development of this technique. Here, through systematic study of the Pb precursor and in situ characterization of the PNCs, it is revealed that the reverse micelle nature of the Pb precursor exactly creates a novel demulsification-crystallization (D-C) model, namely, a two-stage nucleation is divided by a demulsification process for the PNCs. On this basis, a top efficiency for green light-emitting diodes based on PNCs is obtained with a maximum external quantum efficiency of 22.5% through tailoring the D-C model using a multiple-acid-anion synergistic assisted strategy to obtain high-quality PNCs. Beyond the high efficiency, the work paves the way for diverse ideas in PNC synthesis.

Colloidal cesium lead halide (CsPbX

An asymmetric bulky periphery enveloping strategy is proposed to delicately manipulate molecules for the construction of novel multifunctional organic electronic materials. Here, 9,10-diphenylanthracene (DPA) was selected as the framework with both carrier-transporting channel and blue emission, with bulky 1,5-diazarcarbazole (15NCz) and terphenyl/terpyridine grafted on it. Two asymmetric anthracene-containing derivatives, namely 5-(4-(10-(5′-phenyl-[1,1′:3′,1′′-terphenyl]-4-yl)anthracen-9-yl)phenyl)-9H-1,5-diazarcarbazole (p-15NCz3PhDPA) and 9-(4-(10-(4-([3,2′:6′,3′′-terpyridin]-4′-yl)phenyl)anthracen-9-yl)phenyl)-9H-1,5-diazarcarbazole (p-15NCz3PyDPA), were first designed and synthesized. The bulky periphery groups 15NCz and terphenyl/terpyridine with large steric hindrance could efficiently increase the molecular space volume and diminish the intermolecular π–π stacking, which helped to promote the photoluminescence quantum yield (PLQY). Meanwhile, the introduced terphenyl/terpyridine manipulated the charge-carrier-injecting and bipolar-transporting characteristics. A detailed device engineering study was carried out, where it was found that p-15NCz3PhDPA- and p-15NCz3PyDPA-based unilateral homogenous devices could achieve deep-blue emissions with Commission Internationale de L’Eclairage (CIE) coordinates of (0.149, 0.081) and (0.151, 0.106) at a voltage of 6 V, and a narrow full width at half maximum (FWHM) of ∼52 nm and an impressive maximum external quantum efficiency (EQEmax) of 5.87% and 5.80%, respectively. These new multifunctional materials performed better than the commonly used electron-transporting material TPBi. Accordingly, this work sheds light on designing multifunctional organic electronic materials, particularly offering a sensible way to construct efficient low-power-consumption simplified deep-blue fluorescent OLEDs.

Two novel acridine-benzofuran/benzothiophene hybrid donors of 34BxAc (x = F, 34BFAc: 13,13-dimethyl-8,13-dihydrobenzofuro[3,2-a]acridine; x = T, 34BTAc: 13,13-dimethyl-8,13-dihydrobenzo[4,5]thieno[3,2-a]acridine) were developed as aromatic fused donors by combining dimethyl acridine (Ac) with benzofuran and benzothiophene, respectively. As a comparison, the hybrid donors of 12BxAc (x = F, 12BFAc: 5,5-dimethyl-5,13-dihydrobenzofuro[3,2-c]acridine; x = T, 12BTAc: 5,5-dimethyl-5,13-dihydrobenzofuro[3,2-c]acridine) were also prepared. By attaching the TPPM (2,4,6-triphenylpyrimidine) acceptor to these fused hybrid donors (12BFAc, 12BTAc, 34BFAc and 34BTAc), 12BxAc-PM (12FAc-PM and 12BTAc-PM) and 34BxAc-PM (34BFAc-PM and 34BTAc-PM) were further designed and synthesized. It was revealed that 34BxAc-PM was better than 12BxAc-PM at shrinking the singlet–triplet energy gap and decay lifetime, and increasing the photoluminescence quantum yield. The sky-blue thermally activated delayed fluorescent organic light-emitting diodes (OLEDs) with 12BFAc-PM as a dopant just showed a maximum external quantum efficiency (EQE) of 12.9% and a CIEx,y of (0.16, 0.29). The 12BTAc-PM-based device achieved a maximum EQE of 25.6%, however, the efficiency roll-off was relatively serious. In contrast, high-performance and low efficiency roll-off OLEDs can be developed using 34BxAc-PM. For instance, the 34BFAc-PM-based device realized a maximum EQE of 27.7%, and still a high EQE of 24.6% at 1000 cd m−2 and 19.6 cd m−2 at 5000 cd m−2, respectively, indicative of the superiorities of the novel donors (34BFAc and 34BTAc).

By conjugating 10-phenyl-10H-phenothiazine-5,5-dioxide (2PTO) with aromatic amine substituents (PhCz and DMACMN), three novel host materials namely 10-(9-phenyl-9H-carbazol-3-yl)-10H-phenothiazine 5,5-dioxide (3CzNPTO), (10-(4-(9H-carbazol-9-yl)phenyl)-10H-phenothiazine 5,5-dioxide (9CzNPTO) and 10-(4-(9,9-dimethylacridin-10(9H)-yl)-2,5-dimethylphenyl)-10H-phenothiazine 5,5-dioxide (DMACMNPTO) were designed and synthesized. DMACMNPTO with thermally activated delayed fluorescence (TADF) properties exhibited bipolar characteristics resulting from the completely separated HOMO/LUMO distribution. Using DMACMNPTO as a host for TADF emitters, devices showed a maximum external quantum efficiency (EQEmax), current efficiency (CEmax) and power efficiency (PEmax) of 18.3%, 33.3 cd A−1 and 37.4 lm W−1 in blue-emitting diodes, 18.6%, 49.1 cd A−1 and 47.2 lm W−1 in green-emitting diodes, and 19.1%, 59.2 cd A−1 and 66.0 lm W−1 in yellow-emitting diodes, respectively. These results corroborated the potential of phenothiazine dioxide-containing derivatives as host materials in a sequence of color TADF-OLEDs.

Anthracene moieties are suitable for constructing efficient blue-emitting materials. In this study, three novel bipolar anthracene-based compounds 4-(10-(4′-(9H-carbazol-9-yl)-[1,1′-biphenyl]-4-yl)anthracen-9-yl)benzonitrile (pCzphAnBzt), 4-(10-(3-(9H-carbazol-9-yl)phenyl)anthracen-9-yl)benzonitrile (mCzAnBzt) and 4-(10-(3,5-di(9H-carbazol-9-yl)phenyl)anthracen-9-yl)benzonitrile (m2CzAnBzt) were designed and synthesized using Suzuki coupling reactions. We have demonstrated clearly that the chemical structures of the side groups have significant influence on the thermal, photophysical, and electroluminescence properties. The deep-blue emission of the emitter can be realized by restricting the intramolecular π-conjugation, twisting the molecule conformation and introducing a large substituent causing steric hindrance to suppress the π–π stacking interactions. Besides, all three compounds showed excellent performances in nondoped electroluminescent devices, especially mCzAnBzt, which presented deep-blue emission with CIE coordinates of (0.15, 0.07) and a maximum external quantum efficiency of 7.95%. The performance matched NTSC color purity and was one of the best in nondoped deep-blue devices.

Three deep blue thermally activated delayed fluorescence (TADF) molecules are designed by connecting three different sterically hindered electron-donating groups with 2,6-diphenylpyrimidine acceptors. The rigid structures based on carbazole derivatives endow them with excellent thermal stability and high photoluminescence quantum yields (PLQYs) of about 0.72–0.74. A deep blue doped device based on SFI34pPM with a CIEy of 0.09 and a high external quantum efficiency (EQE) of 8.2% is achieved. Also, 3CzPhpPM realizes a maximum EQE of 4.9% with a CIEx,y of (0.15, 0.06). The high PLQY and triplet energy (∼2.84 eV) allow the three deep blue compounds to be used as hosts for yellow TADF emitters, which realized high-performance yellow devices (EQEmax = 18.6%) with alleviated efficiency roll-off. What's more, 3CzPhpPM combined with the TADF sensitizer and the fluorescent material TBRb achieves a high EQE of 19.1%, which is among the best for yellow fluorescent devices. The bipolar transporting ability and the harvesting of triplet excitons together ensure highly efficient yellow devices. Accordingly, these results shed light on the development of designing multifunctional deep blue TADF materials, particularly offering a smart way to construct high efficiency yellow fluorescent devices.

Here, using a strategy called “V-shaped layout of triplet energy levels (ETs)”, a high-T1, electron-deficient and bulky 1,5-diazarcarbazole (15NCz) was first introduced for the construction of new electron-transporting materials (ETMs). When 9,10-diphenylanthracene (DPA) was encapsulated by 15NCz at different positions, a series of ETMs with high electron mobility and good thermal stability were designed and synthesized: 9-(4-(9-([1,1′-biphenyl]-4-yl)anthracen-10-yl)phenyl)-9H-1,5-diazarcarbazole (p-S15NCzDPA), 9-(3-(9-([1,1′-biphenyl]-3-yl)anthracen-10-yl)phenyl)-9H-1,5-diazarcarbazole (m-S15NCzDPA), 9,10-bis(4-(9H-1,5-diazarcarbazole-9-yl)phenyl)anthracene (p-D15NCzDPA) and 9,10-bis(3-(9H-1,5-diazarcarbazole-9-yl)phenyl)anthracene (m-D15NCzDPA). When these novel ETMs were used in triplet–triplet fusion (TTF) fluorescent OLEDs, they exhibited superior performance compared to devices using the common ETMs TPBi and TmPyPB. In particular, devices based on m-S15NCzDPA and m-D15NCzDPA offered a maximum luminance (Lmax) of 66 100 and 66 950 cd m−2, maximum current efficiency (CEmax) of 17.40 and 17.20 cd A−1, and maximum power efficiency (PEmax) of 12.20 and 11.70 lm W−1 with a maximum external quantum efficiency (EQEmax) of 9.00% and 8.66%, respectively. More importantly, the device based on m-D15NCzDPA also achieved lower efficiency roll-offs at high luminance (roll-offs of 2.3% and 13.9% at 10 000 and 50 000 cd m−2, respectively). This work demonstrated that a V-shaped layout of ETs strategy was beneficial for the construction of a series of high-performance ETMs.

In this manuscript, by utilizing limited conjugation of carbazole and easily realizing triplet–triplet annihilation properties of 4-(anthracen-9-yl)benzonitrile, two new blue materials 4-(10-(9-phenyl-9H-carbazol-3-yl)anthracen-9-yl)benzonitrile (3CzAnBzt) and 4-(10-(4-(9H-carbazol-9-yl)phenyl)anthracen-9-yl)benzonitrile (pCzAnBzt) were designed and synthesized. In both cases, these compounds exhibited small energy gap and orbit overlapped between excited state of Tm and Sn, which would accelerate the triplet–triplet annihilation process. Additionally, when these two compounds were used as emitters in nondoped devices, the triplet energy was utilized efficiently through triplet–triplet annihilation, excellent blue electroluminescence performances were achieved. The maximum external quantum efficiency values were 10.06% and 9.23% for 3CzAnBzt and pCzAnBzt, respectively. The efficiency roll-off for 3CzAnBzt and pCzAnBzt were very low, the EQEs still remained 8.97% and 7.10% at the luminescence of 1000 cd m−2. (0.14, 0.14) and (0.14, 0.10) are the Commission International de L’Eclairage coordinates for 3CzAnBzt and pCzAnBzt, respectively, at the voltage of 6 V. Up to now, the outstanding EL performances were the state-of-the-art compared to previously reported nondoped blue EL devices.

Dimethyl acridine (Ac) and carbazole (Cz) donors are fused to produce acridine–carbazole hybrid donors 12AcCz (8,8-dimethyl-5-phenyl-8,13-dihydro-5H-indolo[2,3-c]acridine) and 23AcCz (13,13-dimethyl-7-phenyl-7,13-dihydro-5H-indolo[3,2-b]acridine). By combining the TPPM (2,4,6-triphenylpyrimidine) acceptor with the Ac–Cz-fused donors of 12AcCz and 23AcCz, two emitters, 12AcCz-PM (13-(4-(2,6-diphenylpyrimidin-4-yl)phenyl)-8,8-dimethyl-5-phenyl-8,13-dihydro-5H-indolo[2,3-c]acridine) and 23AcCz-PM (5-(4-(2,6-diphenylpyrimidin-4-yl)phenyl)-13,13-dimethyl-7-phenyl-7,13-dihydro-5H-indolo[3,2-b]acridine), are designed and synthesized. The impact of the different fused topologies of the hybrid donors on the molecular configuration and photophysical and optoelectrical properties is systematically investigated. For 12AcCz-PM, the large steric hindrance between the donor and acceptor compels Ac of 12AcCz to be crooked, which endows it with a relatively planar quasi-axial conformation. No blatant TADF character is observed, but the 12AcCz-PM doped device still presents ultradeep blue emission with CIEx,y of (0.15, 0.05) and a maximum external quantum efficiency (EQEmax) of 6.4%. Whereas, 23AcCz-PM shows a quasi-equatorial conformation and possesses notable TADF behavior. The 23AcCz-PM doped device reachs an EQEmax of 28.4% at low dopant concentration and 26.1% at high dopant concentration. Additionally, low efficiency roll-off (EQEs of 24.8% at 1000 cd m−2 and 20.7% at 5000 cd m−2) further confirms its superiority as a TADF emitter.

A series of 1,2,4-thiadiazole core-based bipolar materials, 2,2′-(1,2,4-thiadiazole-3,5-diyl)bis(N,N-diphenylaniline) (o-TPATHZ), 3,3′-(1,2,4-thiadiazole-3,5-diyl)bis(N,N-diphenylaniline) (m-TPATHZ) and 4,4′-(1,2,4-thiadiazole-3,5-diyl)bis(N,N-diphenylaniline) (p-TPATHZ) were developed as the host matrixes for the deep red phosphorescent emitters tris(1-phenylisoqiunoline) iridium (Ir(piq)3) and [bis(2-methyldibenzo-[f,h]-quinoxaline) Ir(III)(acetylacetonate)] (Ir(MDQ)2(acac)). By systematic studying, we demonstrated that there are two types of charge-trapping effect within the emissive layers through adjusting the host-guest compatibility. And, it is revealed that a symmetric charge-trapping effect can contribute to realizing a stable charge-balance, which led to a mitigating efficiency roll-off at high current density. Consequently, a maximum external quantum efficiency (EQE) of 16.2% was achieved by an optimized device with p-TPATHZ-Ir(piq)3 emissive layer. Remarkably, the EQE still remained as high as 15.7% at the high luminance of 1000 cd/m2.

In this study, 4,6-diphenyl-1,3,5-triazine as the rotor, was firstly introduced to the construction of AIEgens. By conjugating phenyl-9H-carbazole and 4,6-diphenyl-1,3,5-triazine to the 9 or 10 position of anthracene, three new multifunctional aggregation-induced emission (AIE) fluorophores, 3-(10-(4,6-diphenyl-1,3,5-triazin-2-yl)anthracen-9-yl)-9-phenyl-9H-carbazole (3CzAnTrz) 9-(4-(10-(4,6-diphenyl-1,3,5-triazin-2-yl)anthracen-9-yl)phenyl)-9H-carbazole (pCzAnTrz) and 9-(3-(10-(4,6-diphenyl-1,3,5-triazin-2-yl)anthracen-9-yl)phenyl)-9H-carbazole (mCzAnTrz) were designed and synthesized. The photophysical properties indicated that all three compounds not only exhibited an AIE effect but also showed a reversible piezofluorochromic (PFC) behaviour. The experimental results revealed that the spectral shifts ΔλPFC (ΔλPFC = λrepressed – λannealed) were obviously influenced by the linking position of 9-phenyl-9H-carbazole, and 3CzAnTrz showed largest spectral shifts (ΔλPFC = 66 nm), because of the relatively loose molecular packing, weak intermolecular CH-π interactions and more twisted conformation. When three fluorophores were used as emitter in the nondoped sky-blue devices, these devices showed excellent electroluminescence (EL) performances, realizing the maximum current efficiency (CE), power efficiency (PE) and external quantum efficiency (EQE) values of 13.34 cd A−1, 11.59 lm W−1, 5.44%; 11.19 cd A−1, 9.25 lm W−1, 5.54% and 8.74 cd A−1, 6.44 lm W−1, 4.71% for 3CzAnTrz, pCzAnTrz, and mCzAnTrz, respectively. And these devices exhibit negligible efficiency roll-off even at 10000 cd m−2. These results manifest that the potential advantage of multifunctional AIEgens applicable for piezofluorochromism and nondoped high-performance EL devices.

Developing novel thermally activated delayed fluorescence (TADF) materials with a small full-width at half-maximum (FWHM) is very important for the fabrication of wide gamut and high-resolution displays of organic light-emitting diodes (OLEDs). In this work, we report two blue TADF emitters (tDPAC-BN and tDMAC-BN) with narrow FWHM based on a one-shot electrophilic C-H borylation reaction by selecting acridan-containing arylamine derivatives as the starting materials of borylation. The rigid skeleton structure significantly reduces vibrational motion, endowing tDPAC-BN and tDMAC-BN with high PLQYs (94.4% and 89.7%) and narrow FWHMs (19 nm and 26 nm in toluene). The electroluminescent devices employing tDPAC-BN and tDMAC-BN as emitters exhibit external quantum efficiency (EQE) of 21.6% and 22.3%, and CIE coordinates of (0.135, 0.094) and (0.116, 0.186), respectively. More importantly, we found the electrophilic borylation site of borylation reaction can be controlled by varying the steric hindrance effect and electron-donating ability of the substrate substituent. The different HOMO distribution originated from the differences in the substrate substituent accounts for different cyclization mode for tDPAC-BN and tDMAC-BN. Therefore, the work provides a useful strategy for broadening the range of high-performance TADF materials with narrow FWHM.

Formamidinium (FA) lead bromide (FAPbBr3) perovskite nanocrystals (P-NCs) have ultrapure green emission and high stability, while FAPbBr3 NCs based light-emitting diodes (FA-NLEDs) still have little report. Here, FAPbBr3 NCs with a high photoluminescence quantum yield of 85.8% were synthesized. By controlling the concentration of FAPbBr3 NCs in toluene solution, the exciton recombination region was precisely confined to the emitting layer and the parasitic emission coming from electron transport layer disappeared, resulting in the pure green emissions. The optimized FA-NLED presents a maximum external quantum efficiency (EQE), current efficiency (CE) of 3.84% and 16.08 cd/A respectively, with the EL emission peak of 528 nm, CIE of (0.183, 0.763) and a full width of half-maximum (FWHM) of 24 nm, which is among the best performance of FA-NLEDs.

The development of efficient and robust, deep-blue, thermally activated delayed fluorescence (TADF) emitters, especially those matching the European Broadcasting Union (EBU) standard with Commission International de L'Eclairage (CIE) coordinates of (0.15, 0.06), is one of the challenging issues in organic light-emitting devices (OLEDs). Through sophisticated molecular engineering, two novel pyrimidine derivatives with D-π-A configuration, 5-(4-(2,6-diphenylpyrimidin-4-yl)phenyl)-5H-benzofuro[3,2-c]carbazole (pBFCz-26DPPM) and 5-(4-(2,6-diphenylpyrimidin-4-yl)phenyl)-5H-benzo [4,5]thieno[3,2-c]carbazole (pBTCz-26DPPM) have been designed and synthesized. There are only negligible differences in the molecular configuration and thermal, electrochemical and photophysical properties for the two compounds. However, TADF properties can be tuned by changing the heteroatom in the donor moiety. Compound pBFCz-26DPPM offers a shorter delayed fluorescence lifetime (τd) than that of pBTCz-26DPPM. The optimized device serving pBFCz-26DPPM as dopant presents deep-blue Commission Internationale de l’Eclairage (CIE) coordinates of (0.154, 0.054) and maximum external quantum efficiencies (EQEmax) of 6.20%. Remarkably, no-doped device based on pBFCz--26DPPM delivers CIE coordinates of (0.153, 0.067) and EQEs as high as 5.80%. These device performances are amongst some of those of the best performing deep blue TADF OLEDs with similar color gamut.

Here, a phenanthroimidazole moiety was firstly introduced into the construction of thermally activated delayed fluorescence (TADF) emitters, and two novel TADF emitters consisting of phenanthroimidazole as the acceptor group and phenazine as the donor group, 1-(4-(tert-butyl)phenyl)-2-(4-(10-phenylphenazin-5(10H)-yl)phenyl)-1H-phenanthro[9,10-d]imidazole (PPZTPI) and 1-phenyl-2-(4-(10-phenylphenazin-5(10H)-yl)phenyl)-1H-phenanthro[9,10-d]imidazole (PPZPPI) were designed and synthesized. The highly twisted conformation between phenazine and phenanthroimidazole in the molecules results in effective spatial separation of the HOMO and LUMO and small singlet–triplet splittings. Both compounds possess obvious TADF features. Their crystallographic properties, electronic structures, thermal stabilities, photophysical properties, and energy levels are studied systematically. Organic light-emitting diodes (OLEDs) using these two green TADF emitters demonstrate high external quantum efficiencies of 21.06% for PPZPPI and 20.52% for PPZTPI, respectively, which is comparable to most of the previously reported TADF OLEDs.

Molecular structures play a critical role in forming the horizontal orientation of the emission transition dipole of light-emitting TADF materials which can improve the light outcoupling efficiency of OLEDs. Here, two TADF emitters of IndCzpTr-1 and IndCzpTr-2 based indolocarbazole derivatives with stereoscopic and linear structures were designed and synthesized. With a smaller ΔEST, better thermal stability and preferential horizontal orientation with an orientation order parameter S of −0.264, a green TADF OLED device based on IndCzpTr-2 realized a maximum EQE of 30.0% and maximum current efficiency (CE) of 82.6 cd A−1 without using any optical outcoupling technology; meanwhile, a sky-blue TADF OLED with a maximum EQE of 14.5% and a maximum CE of 28.1 cd A−1 was obtained for IndCzpTr-1 with a homologous device structure.

Three novel TADF materials, 10-(6-(2,6-diphenylpyrimidin-4-yl)pyridin-3-yl)-9,9-diphenyl-9,10-dihydroacridine (DPAc-4PyPM), 9,9-diphenyl-10-(4-(2-phenyl-6-(pyridin-2-yl)pyrimidin-4-yl)phenyl)-9,10-dihydroacridine (DPAc-6PyPM) and 10-(4-(2,6-diphenylpyrimidin-4-yl)phenyl)-9,9-diphenyl-9,10-dihydroacridine (DPAc-TPPM) have been designed and synthesized. CH⋯N intramolecular hydrogen-bonding interactions were introduced into pyrimidine–pyridine hybrid acceptors, then the TADF properties can be tuned by skillful manipulation of the positions of CH⋯N in the acceptor moiety. Both DPAc-4PyPM and DPAc-6PyPM exhibit a higher PLQY than DPAc-TPPM. Simultaneously, the kRISC realized for DPAc-4PyPM is nearly 5 or 10 fold higher than that of its analogues. The optimized sky-blue device using DPAc-4PyPM as a dopant demonstrated the maximum external quantum efficiency, current efficiency and power efficiency of 24.34%, 53.89 cd A−1 and 36.79 lm W−1, respectively, which is comparable to most of the previously reported pyrimidine-based TADF OLEDs.

A novel electron acceptor based on 10-phenyl-10H-phenothiazine 5,5-dioxide (2PTO) was introduced for the first time to construct aggregation-induced delayed fluorescence materials. The emitter PXZ2PTO contains phenoxazine as the electron donor, exhibiting both AIE characteristics and TADF properties. Due to the highly stereoscopic structure and small ΔEST of PXZ2PTO, a green non-doped TADF OLED realized a high maximum EQE, CE and PE of 16.4%, 44.9 cd A−1 and 32.0 lm W−1, respectively, without using any optical outcoupling technology, which is comparable with the best reported non-doped TADF OLEDs. In addition, the efficiency of the non-doped devices are comparable with that of doped PXZ2PTO devices, with the maximum EQE, CE and PE of 16.3%, 43.8 cd A−1 and 35.2 lm W−1, respectively.

Deep-blue thermally activated delayed fluorescence (TADF) emitters with National Television System Committee (NTSC) standard (0.14, 0.08) and narrowband emission have been one of the challenging issues for organic light-emitting diodes (OLEDs). In this work, a novel molecular design strategy, periphery cladding, was used to design and synthesize three deep-blue multi-resonance TADF emitters, N,N, 5,9-tetraphenyl-5,9-dihydro-5,9-diaza-13b-boranaphtho[3,2,1-de]anthracen-7-amine (PAB), 2,12-di-tert-butyl-5,9-bis(4-(tert-butyl)phenyl)-N,N-diphenyl-5,9-dihydro-5,9-diaza-13b-boranaphtho[3,2,1-de]anthracen-7-amine (2tPAB) and 2,12-di-tert-butyl-N,N,5,9-tetrakis(4-(tert-butyl)phenyl)-5,9-dihydro-5,9-diaza-13b-boranaphtho[3,2,1-de]anthracen-7-amine (3tPAB). By cladding large steric hindrance tert-butyl unit at periphery of multi-resonance emitter, the intermolecular interactions were suppressed, thus reducing aggregation-induced emission quenching and improving the PLQY of emitter. 3tPAB with full periphery cladding exhibited higher PLQY (74.7%). As a result, the device based on 3tPAB acquired the best performance by using 1,3-di(9H-carbazol-9-yl)benzene (mCP) with low polarity as host. The maximum external quantum efficiency (EQEmax), CIE coordinates, and full-width at half-maximum (FWHM) of 3tPAB-based device were 19.3%, (0.141, 0.076), and 26 nm, respectively. To our knowledge, this is the first report about narrowband TADF OLEDs with single host that EQEmax approaches 20% while CIE coordinates meet the NTSC blue-light standard.

Efficient white organic light-emitting diodes (WOLEDs) with high stability are highly desired nowadays to produce devices that meet the commercial illumination requirement. WOLEDs based on single-host emission layer, is a preferred route to simplify device structures and thus lower the production cost. In this work, we report on single-host WOLEDs based on bipolar material, 2,6-bis[(3-carbazol-9-yl)phenyl)]pyridine (26DCzPPy), as the host, and Iridium (III)bis[(4,6-difluorophenyl)-pyridinato-N,C 2′ ] (FIrpic), [3,2-c]pyridinato-N,C 2′ ) acetylacetonate (PO-01), as blue and yellow dopants, respectively. The devices exhibit not only higher efficiency, but also superior stability compared to the conventional devices and doping-free devices. Detailed analysis is conducted to clarify the underlying reasons. This work enriches the mechanism understanding of single-host devices and paves the way for development of high performance WOLEDs.

A span-new electron-deficient moiety 2,5-diazarcarbazole (25NCz) with high T1 = 2.77 eV was firstly designed and synthesized, which had enormous potential to construct organic electronic materials in photoelectric field. Herein, 25NCz as large rigid-type periphery functionalized group, was introduced to develop novel electron transporting materials (ETMs) by grafting large rigid-type π-conjugated core anthracene. Two novel ETMs p-S25NCzDPA and p-D25NCzDPA were designed and developed. Due to the dual characteristics of rigidity and electron-accepting of the 25NCz, as expected, these two ETMs possessed good thermal stability and high electron mobility. When triplet-triplet fusion (TTF) sky-blue fluorescent OLEDs based on these two novel ETMs were manufactured, they exhibited superior performances. In particular, the maximum external quantum efficiency (EQE) reached 7.45% and the EQE kept 7.45% at the luminance of 50,000 cd m−2 for p-S25NCzDPA based device. This work rationally demonstrated that the significance of newly developed electron-deficient moiety 25NCz in designing ETMs for high-performance OLEDs.

Efficient phosphorescent white organic light-emitting devices (WOLEDs) based on a novel phosphine oxide host, 4,6-bis(diphenylphosphoryl)dibenzofuran (DBFDPO), with particularly low turn-on voltage and high color stability are reported. Without any electrical doping (p-doing or n-doping) strategies, the simplified optimal WOLEDs utilizing DBFDPO as the same host for blue/yellow emitters show low operating voltages, 1 cd/m 2 at 2.5 V (turn-on voltage), 46 cd/m 2 at 3 V and 2787 cd/m 2 at 5 V, and 12840 cd/m 2 at 7 V, respectively. A forward-viewing current efficiency (CE) of 41.3 cd/A (power efficiency (PE) of 34.0 lm/W) is achieved at the luminance of 673.4 cd/m 2 without any out-coupling enhancement structures. Furthermore, improved color stability is achieved through adjusting the yellow emitting layer. The Commission Internationale de I’Eclairage coordinates (CIE) of the optimal WOLED merely shift from (0.330, 0.405) to (0.327, 0.400) over a wide range of luminance (10–10,000 cd/m 2 ). We have revealed that the competition of the two mechanisms of energy transfer and carrier-trapping/-assist transport severely impact on the spectra stability.

CsPbBr3 nanocrystals (NCs) with enhanced photoluminescence quantum yield (PLQY) and stability have been regarded as promising emissive materials in flexible, low-cost, and high-definition display applications. The long-chain organic ligands, i.e. oleylamine and oleic acid, are essential to stabilize the NCs and increase their PLQY, but the long-chain ligands show detrimental effects on the charge transport ability of the resultant NCs, which deteriorate the performance of light emitting diodes (LEDs). Here, we introduced Na+ ions during the synthesis of perovskite NCs. Because of strong ionic bonding between Na+ and Br− ions, the introduced Na+ ions could stabilize the Br− ions hanged on the surface, which is beneficial to suppressing the generation of Br− vacancies. In addition, when the Na+ ions were capped on perovskite surface, the amount of long-chain organic ligands on the surface of perovskite NCs were reduced. As a result, high-quality perovskite NCs with uniform microstructure, high PLQY of 84.6%, and improved charge transport ability are achieved with appropriate addition of Na+ ions, which enables us increase the EQE of a LED device from 5.59% to 7.33%.

Herein, large π-conjugated core anthracene with an innate bipolar property was employed to construct multifunctional organic electronic materials. Delicate manipulating molecules via combining anthracene core and large periphery groups, two asymmetric anthracene derivatives namely (4-(10-(4-(9H-1,5-diazacarbazole-9-yl)phenyl)anthracen-9-yl)phenyl)diphenylphosphine oxide (p-PO15NCzDPA) and (3-(10-(3-(9H-1,5-diazarcarbazole-9-yl)phenyl)anthracen-9-yl)phenyl)diphenylphosphine oxide (m-PO15NCzDPA) were firstly designed and developed. The large periphery groups 1,5-diazarcarbazole (15NCz) and diphenylphosphine oxide (PO) efficiently interrupt the intramolecular π-conjugation, presenting an asymmetric bulky periphery enveloping strategy achieving highly twisted structures, which help to realize deep-blue emission. Meanwhile, due to the high PLQY and well-balanced bipolar transport characteristics, desired device addressing the contradiction of efficiency, color gamut and structure complexity is within reach. Detailed device engineering study was carried out, in which p-PO15NCzDPA and m-PO15NCzDPA were functioned as multifunction layers. As expected, p-PO15NCzDPA-based homogenous and unilateral homogenous OLEDs exhibited outstanding performance with impressive EQEmax of 4.55% and 6.40%, deep blue CIE coordinates of (0.152, 0.075) and (0.151, 0.066) at the voltage of 6 V, narrow FWHM of 46 nm and 50 nm, respectively. More importantly, the simplified homogenous device achieved extremely low efficiency roll-offs of 1.3% and 4.8% at 1000 and 5000 cd m−2, respectively. These results are among the most outstanding performance, which provided a guide for further improving the performance of deep blue fluorescent OLEDs and simplifying the structure of OLEDs.

Efficient deep-blue thermally activated delayed fluorescence (TADF) emitters are still very scarce. It is available to render the color bluer by reducing the intensity of intramolecular charge transfer (ICT) between acceptor and donor. Here, attaching the acceptor of six-membered heterocyclic diphenylsulfone-derivative (2PTO) with donors (DMAc and DPAc), two compounds, 2-(9,9-dimethyl-acridin-10(9H)-yl)-10-phenyl-10H-phenothiazine 5,5-dioxide (DMAC2PTO) and 2-(9,9-diphenylacridin-10(9H)-yl)-10-phenyl-10H-phenothiazine 5,5-dioxide (DPAC2PTO) were designed and synthesized. Due to the largely twisted configuration and weak ICT, DMAC2PTO with small singlet-triplet energy gap (ΔEST) displayed TADF feature and deep-blue emission. Moreover, DPAC2PTO exhibited much lower photoluminescence quantum yield (PLQY) than DMAC2PTO. The doped device of DMAC2PTO achieved a maximum external quantum efficiency (EQEmax) of 15.2% with a deep-blue color coordinate (CIEx,y) of (0.154, 0.108), and showed a narrow emission spectra with a 52 nm full width at half maximum (FWHM). In addition, the non-doped device of DMAC2PTO reached the EQEmax of 8.36% with CIEx,y of (0.158, 0.157).

Formamidinium lead bromide (FAPbBr(3)) nanocrystals (NCs) demonstrate great potential in light-emitting diode (LED) applications due to their pure green emission and excellent stability. However, t ...

In this paper, the periphery of aggregation-induced emission-thermally activated delayed fluorescence (AIE-TADF) chromophore (DPS-PXZ) was modified with host-substituents (DCB, mCP, pPhDCz and mPhDCz). Four self-host TADF emitters, namely DCB-DPS-PXZ, mCP-DPS-PXZ, pPhDCzDPSPXZ and mPhDCzDPSPXZ, were designed and synthesized. Here, the effect of host-substituents with different linking topologies on TADF has been investigated. Among them, the pPhDCz and mPhDCz substituted AIE-TADF emitters have stronger AIE effect than that of DCB and mCP based ones, which due to the larger twist angle between host substituents and DPS-PXZ. And then, mPhDCzDPSPXZ and pPhDCzDPSPXZ could obtain the PLQYs of 56% and 55% in the neat film, respectively. The PLQY values were higher than that of DCB-DPS-PXZ (40%) and mCP-DPS-PXZ (47%). Based on these advantages, the maximum EQE and the efficiency roll-off at 1000 cd/m2 of the non-doped OLEDs were 18.1% and 7.7% for mPhDCzDPSPXZ, 17.1% and 9.9% for pPhDCzDPSPXZ, respectively. However, the maximum EQEs of DCB-DPS-PXZ and mCP-DPS-PXZ based non-doped devices were only 13.9% and 14.7%, respectively. Therefore, the careful modification of the AIE-TADF chromophore by changing host-substituent types and linking positions appropriately was beneficial for the realization of efficient and low efficiency roll-off non-doped OLEDs.

The nondoped thermally activated delayed fluorescence (TADF) devices are increasingly attracting attention due to the superior performances and simple fabrication process. By incorporating two acceptors with phenothiazine, two materials 2-(10H-phenothiazine-10-yl)-10-phenyl-10H-phenothiazine-5,5-dioxide (PTZ-2PTO) and 3-(10H-phenothiazin-10-yl)-10-phenylacridin-9(10H)-one (PTZ-AD) are designed and investigated. Both the two materials possess dual conformations, whereas the quasi-axial conformer is the main configuration of PTZ-2PTO and quasi-equatorial conformer of PTZ-AD is more stable. The quasi-axial conformers show classical fluorescence emission, and the quasi-equatorial conformers exhibit TADF characteristic. Fascinatingly more, efficient energy transfer can be achieved between quasi-axial conformers and quasi-equatorial conformers, exhibiting similar mechanism to the traditional host-guest system. Based on this characteristic, yellow nondoped TADF-OLED device of PTZ-AD has realized the efficiency of up to 17.08%, 50.48 cd A−1 and 60.04 lm W−1. Meanwhile, the PTZ-AD based nondoped device exhibits low turn-on voltage and low efficiency roll-off, which is among the best performance for yellow nondoped TADF devices. In addition, PTZ-AD based doped device realizes high efficiency of 20.23%, 61.04 cd A−1 and 68.45 lm W−1. This dual conformations forming host-guest system provides a new strategy for obtaining highly efficient nondoped OLEDs devices.

High power efficiency (PE) p-bis(p-N,N-diphenyl-aminostyryl)benzene (DSA-ph) based fluorescent blue organic light-emitting diode (OLED) is demonstrated by utilizing intermixed host (IH) structure. The PE outperforms those devices based on single host (SH), mixed host (MH), and double emitting layers (DELs). By further optimizing the intermixed layer, peak PE of the IH device is increased up to 8.7 lm/W (1.7 times higher than conventional SH device), which is the highest value among the DSA-ph based blue device reported so far.

We have demonstrated color-stable and efficient tandem organic light-emitting devices (OLEDs) using 4,7-diphenyl-1,10-phenanthroline (Bphen):LiF/4,4′,4″-tris(N-3-methylphenyl-N-phenyl-amino)triphenylamine (m-MTDATA):molybdenum oxide (MoO x ) as charge generating unit (CGU), which has the advantages of air stability and ease of fabrication; the working mechanism of Bphen:LiF/m-MTDATA:MoO x is also discussed through analysis of the electrical and spectral emission properties of tandem devices with different CGUs. The performance of tandem white OLED, comprising blue and yellow phosphorescent EL units, can be improved by optimizing the thickness of Bphen:LiF layer. The device comprised of 30 nm Bphen:LiF layer has a maximum current efficiency of 38.7 cd/A and it can still maintain 24.6 cd/A at the luminance of 10,370 cd/m 2 . Moreover, the Commission Internationale de L'Eclairage (CIE) coordinates of the device are rather stable and the variation is only (± 0.003, ± 0.007) over a wide range of luminance (100–13,000 cd/m 2 ).

Single emission layer white organic light-emitting diodes (WOLEDs) showing high color stability, low turn-on voltage, high efficiency and low efficiency roll-off by incorporating iridium(III) bis[(4,6-difluo-rophenyl)-pyridinato-N,C2] (FIrpic) and bis(2-phenylbenzothiazolato) (acetylacetonate)iridium(III) (Ir(BT)2(acac)) phosphors dyes have been demonstrated. Our WOLEDs without any out-coupling schemes as well as n-doping strategies show low operating voltages, low turn-on voltage (defined for voltage to obtain a luminance of 1 cd/m2) of 2.35 V, 79.2 cd/m2 at 2.6 V, 940.5 cd/m2 at 3.0 V and 10 300 cd/m2 at 4.0 V, respectively, and achieve a current efficiency of 40.5 cd/A, a power efficiency of 42.6 lm/W at a practical brightness of 1000 cd/m2, and a low efficiency roll-off 14.7% calculated from the maximum efficiency value to that of 5000 cd/m2. Such improved properties are attributed to phosphors assisted carriers transport for achieving charge carrier balance in the single light-emitting layer (EML). Meanwhile the host–guest energy transfer and direct exciton formation process are two parallel pathways serve to channel the overall excitons to dopants, greatly reduced the unfavorable energy losses.

We have demonstrated white organic light-emitting diodes (WOLEDs) based on a yellow phosphorescence iridium complex and an efficient blue fluorescence. The property of the blue fluorescence is studied and the pure blue device can obtain a peak current efficiency (CE) of 8.5 cd/A. The best obtained WOLED shows a peak CE of 24.7 cd/A at 1000 cd/m2 with Commission Internationale De L'Eclairage coordinate of (0.44, 0.48), while WOLEDs based on different architectures exhibit good color stability.

Inverted top-emitting organic light-emitting diodes (ITOLEDs) with aluminum as cathode and semitransparent silver as anode are investigated. Comparing the blue, green and red ITOLEDs with conventional BEOLEDs based on iridium complex, it is surprising that the red ITOLED exhibits a higher efficiency nearly twice as that of the bottom-emitting counterpart, while blue and green ITOLEDs are comparable to BEOLEDs. We explain that the role of the strong microcavity effect improved the spontaneous emission of emitters in all ITOLEDs, however, only the intrinsic quantum yield of the red emitters is improved due to its comparable radiative and nonradiative decay rates.

We systematically studied the influence of weak microcavity effects on the optical properties of tandem white organic light-emitting diodes (WOLEDs) using optical simulation. Based on the simulation results, an image processing method is developed and verified for rational design of high-performance tandem WOLEDs. The results indicate that low operating voltage, good color rendering index, and angular emission properties can be simultaneously obtained in tandem WOLEDs by engineering the device structure. This study provides promising direction for the development of high-performance tandem WOLEDs.

The fabrication of planar heterojunction (PHJ) organic photovoltaic (OPV) cells using tetramethyl substituted copper(II) phthalocyanine (CuMePc) as an electron donor and C60 as an acceptor is described. The impact of post-fabrication thermal annealing upon the performance of these cells has been examined. Atomic force microscopy (AFM) images and UV–visible absorption spectra of CuMePc thin films revealed crystallization of CuMePc induced by thermal annealing at 190 °C. The crystallized CuMePc films accounted for improved hole mobility, broadened absorption spectrum, and increased donor/acceptor interface in the as-fabricated cells after thermal annealing. AFM images also revealed that the surface of MoO3 film was smooth and close-packed after thermal annealing, which efficiently blocked the leakage current in the annealed cells, leading to dramatic improvement of performance for the PHJ cells using CuMePc as the electron donor and MoO3 or V2O5 as the anode buffer layer. The power conversion efficiency of the thermal-annealed PHJ cell with a configuration of ITO/MoO3/CuMePc/C60/Bathocuproine/Al was higher than that of the bulk heterojunction (BHJ) cell fabricated by co-depositing CuMePc and C60. It was mainly because the isolated clusters of CuMePc and/or C60 molecules formed during the fabrication of the BHJ cell was avoided in the PHJ cell.