High power-efficiency solution-processed red phosphorescent organic light-emitting diodes (s-PhOLEDs) are urgently needed in OLED displays and lighting applications. Herein, we have synthesized a novel solution-processable red heteroleptic iridium complex bis[2-di(p-methoxyphenyl) amino (9,9-diethylfluoren-2-yl)-5-(trifluoromethyl) pyridine][acetylacetonate] iridium(III), i.e. Ir(DPA-Flpy-CF3)2acac, which shows efficient red photoluminescence with an emission peak located at 602 nm. This novel red phosphor possesses a high absorption coefficient in the long wavelength region, ensuring the efficient energy transfer from the interfacial exciplex host to the phosphor guest at low phosphor-doping concentration. The optimized red s-PhOLED based on the red Ir(DPA-Flpy-CF3)2acac shows a maximum external quantum efficiency of 19.3% and a power efficiency of 44.5 lm W−1 with Commission International de L'Eclairage (CIE) coordinates of (0.64, 0.36). It is so far the highest power efficiency ever reported for red s-PhOLEDs and is comparable to state-of-the-art red PhOLEDs prepared by thermal evaporation.

Organometal halide perovskites (OHPs) are becoming a hot topic in the field of display and lighting. Unlike the strategy used for solar cells, that is, using several hundred nanometers thick OHP film for fully absorbing solar light to convert electricity, thin-film OHPs (<50 nm) are advantageous to restrain its self-absorption drawback and thus beneficial for preparing efficient light-emitting diodes (LEDs). Here we manipulate the excess molar ratio of MABr/PbBr2 precursors and the post-annealing temperature to obtain uniform thin-film OHPs and suppress the nonradiative defects. Using this simple process, high efficient green perovskite light-emitting diode (PeLED) was obtained, with a maximum luminance of 6124 cd m–2, current efficiency of 15.26 cd A–1, and external quantum efficiency of 3.38%, which is nearly three-fold enhancement with respect to the previous reported best PeLED based on thin perovskite films (<50 nm)

The emissive layer morphology strongly correlates with the charge transport and light-emitting performance of solution-processed phosphor-doped organic light-emitting diodes (PhOLEDs). Herein, morphology manipulation of the solution-processed emissive layer comprising of carbazole dendrimer (H2) host:blue phosphor (FIrpic) guest is realized via processing of the solvent and its influence on charge transport and light-emitting properties is investigated. The formation of H2 aggregates within its amorphous matrix processed with the toluene:p-xylene solvent mixture distinctively improves the hole and electron transport within the emissive layer, helping to lower the driving voltages and improve the light-emitting efficiency. However, excess aggregation of H2 would result in non-uniform dispersion of the FIrpic guest within the H2 host, leading to non-complete host-to-guest energy transfer and decreased electroluminescence performance. Through manipulation of the aggregates within the H2 host by varying the solvent mixture ratio, the trade off between charge transport and energy transfer is realized. Finally, the solution-processed blue PhOLED with optimized emissive layer morphology processed with toluene:p-xylene (9:1) solvent mixture achieves a high light-emitting efficiency of 27.8 cd A−1, corresponding to 25% enhancement compared to 22.2 cd A−1 of the control device processed with commonly used toluene solvent.

•A new deep-red phosphor is designed and synthesized.•It presents high thermal stabilities, excellent solubility and good compatibility with common host materials.•The solution-processed deep-red device shows CIE of (0.68, 0.31) and EQE of 8.2%.•The solution-processed WOLED shows an excellent high CRI value of 89 as well as low CCT of 2331 K.The exploitation of soluble and efficient deep-red phosphorescent emitters is of paramount importance for solution-processed organic light-emitting diodes (OLEDs) applied in both high-quality RGB displays and high color-rendering-index (CRI) solid-state lighting source. In this work, a new deep-red heteroleptic iridium(III) complex, i.e. bis[2,5-di(4-hexylthiophen-2-yl)pyridine][acetylacetonate]iridium(III) [Ir(ht-5ht-py)2(acac)], has been synthesized and successfully used to fabricate solution-processed saturated red and white organic light-emitting diodes (WOLEDs). The long alkyl side-chains of Ir(ht-5ht-py)2(acac) render its excellent solubility in common organic solvents and good compatibility with common host materials. The solution-processed red OLED based on Ir(ht-5ht-py)2(acac) exhibited a decent external quantum efficiency of 8.2% and a power efficiency of 6.5 lm/W, with satisfactory Commission International de L’Eclairage (CIE) coordinates of (0.68, 0.31) for saturated red emission. Furthermore, the prepared multiple-phosphors-doped WOLED with Ir(ht-5ht-py)2(acac) as the red emitter showed an excellent high color rendering index (CRI) value of 89 as well as low color-correlated temperature (CCT) of 2331 K, which can meet the call for physiologically-friendly indoor illumination.

•Polymers with arylcarbazolyl chromophores have been synthesized.•Electro-active layers of the materials were tested in OLEDs.•An electroluminescent OLED with Alq3 emitter demonstrated efficiency of 3.3 cd/A.Monomers and their polymers containing 3-arylcarbazolyl electrophores have been synthesized by the multi-step synthetic route. The materials were characterized by thermo-gravimetric analysis, differential scanning calorimetry and electron photoemission technique. The polymers represent materials of high thermal stability having initial thermal degradation temperatures in the range of 331–411 °C. The glass transition temperatures of the amorphous polymeric materials were in the rage of 148–175 °C. The electron photoemission spectra of thin layers of monomers showed ionization potentials in the range of 5.6–5.65 eV. Hole-transporting properties of the polymers were tested in the structures of organic light emitting diodes with Alq3 as the green emitter. The device containing hole-transporting layers of polyether with 3-naphthylcarbazolyl groups exhibited the best overall performance with a maximum current efficiency of 3.3 cd/A and maximum brightness of about 1000 cd/m2.

•Polymers containing pendant chromophores have been synthesized and characterized.•The materials were tested as host materials of electro-phosphorescent OLEDs.•An efficient device with current efficiency of about 17 cd/A was demonstrated.Polystyrenes containing electronically isolated harmane, phenoxazine or carbazole rings were synthesized and characterized by NMR spectroscopy, elemental analysis and gel permeation chromatography. The new polymers represent amorphous materials of high thermal stability with glass-transition temperatures of 139–179 °C. The electron photoemission spectra of layers of the synthesized polymers showed ionization potentials of about 5.6–6.0 eV. The polymers were tested as host materials in phosphorescent green OLEDs with bis(2-phenylpyridine)(acetylacetonato)iridium(III) as the guest. The device based on polymer containing phenoxazine fragments exhibited the best overall performance with a turn-on voltage of 2.8 V, maximum photometric efficiency of about 17 cd/A and maximum brightness of 2920 cd/m2.

•Phase separation in solution-processed OLEDs is restrained by adjusting processing solvent.•The solution-processed emissive layer is denser than the vacuum-evaporated counterpart.•Efficient solution-processed blue OLEDs with halogen-free solvent are achieved with power efficiency of 15.6 lm/W.Efficient solution-processed blue phosphorescent organic light-emitting diodes (OLEDs) featuring with halogen-free solvent processing are fabricated in this study. The organic molecule 3,6-bis(diphenylphosphoryl)-9-(4′-(diphenylphosphoryl) phenyl)-carbazole (TPCz) that possesses good solubility in halogen-free polar solvents is selected to serve as the host of blue phosphorescent iridium(III) [bis(4,6-difluorophenyl)-pyridinato-N,C2]-picolinate (FIrpic) dopant. The morphology of the TPCz:FIrpic emissive layer prepared with different polar solvents including chlorobenzene (CB), n-butanol (ButA) and isopropanol (IPA) and the effect on their electroluminescent performance have been investigated in detail. It is found that the more polar halogen-free solvent IPA restrains the FIrpic aggregation and renders a more densely packed emissive layer as compared to the CB-processed counterpart, which results in the enhanced electroluminescent performance. The luminous efficiency and power efficiency of the blue phosphorescent OLEDs prepared with CB are merely 5.7 cd/A and 3.3 lm/W, respectively. When using more polar halogen-free solvent IPA, the efficiencies are enhanced to 22.3 cd/A and 15.6 lm/W, about 2.9 and 3.7-time increment, respectively. This work provides an approach to fabricate efficient solution-processed phosphorescent OLEDs with environmental-friendly solvents, which is highly required in large-scale solution-processed manufacturing.Graphical abstractEfficient solution-processed blue phosphorescent organic light-emitting diodes featuring with environmental-friendly solvent processing are fabricated in this study. The morphology of the TPCz:FIrpic emissive layers prepared with different polar solvents including chlorobenzene, n-butanol and isopropanol and the effect on its electroluminescent performance is investigated in detail. It is found that the phase separation morphology in the film spin-cast from chlorobenzene can be effectively restrained by using the more polar halogen-free solvents n-butanol and isopropanol, which results in the increased electroluminescent performance. When using isopropanol to replace chlorobenzene, the power efficiency is enhanced from 3.3 lm/W to 15.6 lm/W.

The morphology of fluorescent polyfluorene (PF) derivatives has strong effects on their electroluminescent (EL) performance. Herein, the influence of processing solvents on the morphology of PF-based white emissive polymer and its correlation to the EL behavior is studied. It is found that the PF copolymer films prepared from chlorobenzene:toluene (CB:TOL) solvent mixtures show stronger tendency to form crystalline α phase PF upon thermal annealing than those prepared from pure TOL or CB solvents. The evaporation rate difference in solvent mixtures can assist in the formation of crystal nucleus and enhance the crystallinity of PF backbone after thermal annealing. The results also reveal that the solvent mixture-processed fluorescent PF-based white emissive polymer not only shows more efficient blue emission, but also more balanced electron and hole transport. Accordingly, both the white emission purity and the light-emitting efficiency of the light-emitting diodes based on PF-based white emissive polymer are greatly enhanced.

The emissive layer morphology strongly correlates with the charge transport and light-emitting performance of solution-processed phosphor-doped organic light-emitting diodes (PhOLEDs). Herein, morphology manipulation of the solution-processed emissive layer comprising of carbazole dendrimer (H2) host:blue phosphor (FIrpic) guest is realized via processing of the solvent and its influence on charge transport and light-emitting properties is investigated. The formation of H2 aggregates within its amorphous matrix processed with the toluene:p-xylene solvent mixture distinctively improves the hole and electron transport within the emissive layer, helping to lower the driving voltages and improve the light-emitting efficiency. However, excess aggregation of H2 would result in non-uniform dispersion of the FIrpic guest within the H2 host, leading to non-complete host-to-guest energy transfer and decreased electroluminescence performance. Through manipulation of the aggregates within the H2 host by varying the solvent mixture ratio, the trade off between charge transport and energy transfer is realized. Finally, the solution-processed blue PhOLED with optimized emissive layer morphology processed with toluene:p-xylene (9:1) solvent mixture achieves a high light-emitting efficiency of 27.8 cd A−1, corresponding to 25% enhancement compared to 22.2 cd A−1 of the control device processed with commonly used toluene solvent.

High power-efficiency solution-processed red phosphorescent organic light-emitting diodes (s-PhOLEDs) are urgently needed in OLED displays and lighting applications. Herein, we have synthesized a novel solution-processable red heteroleptic iridium complex bis[2-di(p-methoxyphenyl) amino (9,9-diethylfluoren-2-yl)-5-(trifluoromethyl) pyridine][acetylacetonate] iridium(III), i.e. Ir(DPA-Flpy-CF3)2acac, which shows efficient red photoluminescence with an emission peak located at 602 nm. This novel red phosphor possesses a high absorption coefficient in the long wavelength region, ensuring the efficient energy transfer from the interfacial exciplex host to the phosphor guest at low phosphor-doping concentration. The optimized red s-PhOLED based on the red Ir(DPA-Flpy-CF3)2acac shows a maximum external quantum efficiency of 19.3% and a power efficiency of 44.5 lm W−1 with Commission International de L'Eclairage (CIE) coordinates of (0.64, 0.36). It is so far the highest power efficiency ever reported for red s-PhOLEDs and is comparable to state-of-the-art red PhOLEDs prepared by thermal evaporation.