Huiren Peng

Sky-blue nondoped OLEDs based on new AIEgens: ultrahigh brightness, remarkable efficiency and low efficiency roll-off

Two novel AIEgens decorated with fluorenyl and dimesitylboryl groups are prepared. They show high thermal stability and excellent solid-state photoluminescence efficiency. Sky-blue nondoped OLEDs are achieved based on them, affording remarkable electroluminescence efficiencies (12.2 cd A−1 and 5.3%), ultrahigh brightness (92810 cd m−2) and low efficiency roll-off (11.0 cd A−1 at 1000 cd m−2).

Improving Electron Mobility of Tetraphenylethene-Based AIEgens to Fabricate Nondoped Organic Light-Emitting Diodes with Remarkably High Luminance and Efficiency

Robust light-emitting materials with strong solid-state fluorescence as well as fast and balanced carrier transporting ability are crucial to achieve high-performance organic light-emitting diodes (OLEDs). In this contribution, two linear tetraphenylethene (TPE) derivatives (TPE-TPAPBI and TPE-DPBI) that are functionalized with hole-transporting triphenylamine and/or electron-transporting 1,2-diphenyl-1H-benzimidazole groups are synthesized and fully characterized. Both TPE-TPAPBI and TPE-DPBI have aggregation-induced emission attributes and excellent photoluminescence quantum yields approaching 100% in vacuum deposited films. They also possess good thermal property, giving high decomposition temperatures (480 and 483 °C) and glass-transition temperatures (141 and 157 °C). TPE-TPAPBI and TPE-DPBI present high electron mobilities of 1.80 × 10(-5) and 1.30 × 10(-4) cm(2) V (-1) s(-1), respectively, at an electric field of 3.6 × 10(5) V cm(-1), which are comparable or even superior to that of 1,3,5-tri(1-phenylbenzimidazol-2-yl)benzene. The nondoped OLED device employing TPE-TPAPBI as active layer performs outstandingly, affording ultrahigh luminance of 125 300 cd m(-2), and excellent maximum external quantum, power and current efficiencies of 5.8%, 14.6 lm W(-1), and 16.8 cd A(-1), respectively, with very small roll-offs, demonstrating that TPE-TPAPBI is a highly promising luminescent material for nondoped OLEDs.

Efficient vacuum-free-processed quantum dot light-emitting diodes with printable liquid metal cathodes

Colloidal quantum dot light-emitting diodes (QLEDs) are recognized as promising candidates for next generation displays. QLEDs can be fabricated by low-cost solution processing except for the metal electrodes, which, in general, are deposited by costly vacuum evaporation. To be fully compatible with the low-cost solution process, we herein demonstrate vacuum-free and solvent-free fabrication of electrodes using a printable liquid metal. With eutectic gallium-indium (EGaIn) based liquid metal cathodes, vacuum-free-processed QLEDs are demonstrated with superior external quantum efficiencies of 11.51%, 12.85% and 5.03% for red, green and blue devices, respectively, which are about 2-, 1.5- and 1.1-fold higher than those of the devices with thermally evaporated Al cathodes. The improved performance is attributable to the reduction of electron injection by the native oxide of EGaIn, which serves as an electron-blocking layer for the devices and thus improves the balance of carrier injection. Also, the T50 half-lifetime of the vacuum-free-processed QLEDs is about 2-fold longer than that of the devices with Al cathodes. Our results demonstrate that EGaIn-based solvent-free liquid metals are promising printable electrodes for realizing efficient, low-cost and vacuum-free-processed QLEDs. The elimination of vacuum and high-temperature processes significantly reduces the production cost and paves the way for industrial roll-to-roll manufacturing of large area displays.

The synthesis of novel AIE emitters with the triphenylethene-carbazole skeleton and para-/meta-substituted arylboron groups and their application in efficient non-doped OLEDs

Four novel aggregation-induced emission (AIE)-active luminogens (p-DPDECZ, p-DBPDECZ, m-DPDECZ and m-DBPDECZ) with triphenylethene-carbazole skeleton and para-/meta-substituted arylboron groups have been synthesized. Their structures are fully characterized using elemental analysis, mass spectrometry and proton nuclear magnetic resonance spectroscopy. The thermal stabilities, photophysical properties, electronic structures, and electrochemical properties of these molecules are investigated systematically using thermal analysis, UV-vis absorption spectroscopy, fluorescence spectroscopy, theoretical calculation and electrochemical methods. The effects of donor–acceptor interaction and conjugation degree on the photoluminescent and electroluminescent properties of these compounds are investigated. The results show that these donor–AIE–acceptor type compounds exhibit good thermal stability and electrochemical stability as well as AIE properties. Non-doped fluorescent OLEDs fabricated by using para-linked p-DPDECZ as an emitting layer emits a green light with a turn-on voltage of 4.8 V, a maximum brightness of 30 210 cd m−2 and a maximum current efficiency of 9.96 cd A−1. While the OLED prepared with meta-linked m-DBPDECZ exhibits efficient blue light emission with a maximum current efficiency of 4.49 cd A−1 and a maximum luminance of 16 410 cd m−2. The electroluminescence properties of these compounds demonstrate their potential application in OLEDs.

Highly transparent quantum-dot light-emitting diodes with sputtered indium-tin-oxide electrodes

Transparent, all-solution processed quantum-dot light-emitting diodes (QD-LEDs) are developed in this work. Indium-tin-oxide (ITO) fabricated by sputtering is adopted as transparent electrodes for the QD-LEDs. To reduce the plasma damage caused by sputtering, ZnO nanocrystals with a thickness of 82 nm are employed as the buffer layer and the electron transport layer. As a result, damage-free QD-LEDs are demonstrated with a high averaged transparency of 70%. The transparent QD-LEDs exhibit an external quantum efficiency of 5% (current efficiency of 7 cd A−1), which is comparable to that of the devices with conventional Al electrodes.

Dimesitylboryl-functionalized tetraphenylethene derivatives: efficient solid-state luminescent materials with enhanced electron-transporting ability for nondoped OLEDs

Organic electroluminescent materials that can simultaneously serve as light-emitting and electron-transporting layers in one organic light-emitting diode (OLED) are very useful for simplifying device configuration, but there are not many. In this work, three tailored luminescent materials (TPE-DB, TPE-BPDB and TPE-TPDB) adopting tetraphenylethene (TPE) and dimesitylboryl groups as the π-conjugated backbone and the electron-deficient functional group, respectively, are synthesized and fully characterized. Their thermal, photophysical, electronic, electrochemical, and electroluminescent properties are investigated systematically. The results reveal that these new dimesitylboryl-functionalized TPE derivatives feature aggregation-induced emission (AIE) characteristics with high fluorescence quantum yields of 81–86% in solid films. They possess high glass-transition temperatures of 134–168 °C and very low LUMO energy levels down to −2.9 eV. The OLED device [ITO/HATCN (20 nm)/NPB (40 nm)/TPE-DB (60 nm)/LiF (1 nm)/Al (100 nm)] that is fabricated by adopting TPE-DB as both the light emitter and electron transporter exhibits excellent electroluminescent performance, with high efficiencies of up to 13.5 cd A−1 and 4.6%, which are advanced noticeably relative to those attained from the device with an additional electron-transporting layer (TPBi). The results demonstrate that these new TPE derivatives are promising n-type solid-state luminescent materials with practical utility in nondoped OLEDs.

Efficient Quantum-Dot Light-Emitting Diodes With 4,4,4-Tris(N-Carbazolyl)-Triphenylamine (TcTa) Electron-Blocking Layer

4,4,4-tris(N-carbazolyl)-triphenylamine (TcTa) with low electron mobility are used as electron-blocking layer (EBL) for quantum-dot light-emitting diodes (QD-LEDs). With TcTa EBL, electrons are effectively blocked, while holes are efficiently injected; consequently, the developed QD-LEDs exhibit significantly improved performance. Maximum external quantum efficiency of 5% and maximum luminance of 16710 cd/m2 are achieved, which represent a 2.7-fold and a 2-fold improvement, respectively, compared with those of the devices without TcTa EBL.

Steric, conjugation and electronic impacts on the photoluminescence and electroluminescence properties of luminogens based on phosphindole oxide

Aggregation-induced emission (AIE) is currently receiving intense interest because of its important implications in photophysics. The structure-property relationship decipherment of AIE luminogens is of crucial importance for the fundamental understanding and application exploration. In this research, a series of novel luminogens based on phosphindole oxide (PIO), including a peculiar one with a folded conformation and apparent through-space conjugation, were synthesized and studied as models to elucidate the AIE mechanism. The significant impacts of steric, conjugation and electronic effects on the AIE property are presented based on the results of crystallography analysis, optical spectra measurements and theoretical computation. Non-doped yellow organic light-emitting diodes were fabricated with the new PIO-based luminogens, and they exhibited high brightness, good electroluminescence efficiencies and low efficiency roll-off.

Synthesis, aggregation-induced emission and electroluminescence properties of a novel compound containing tetraphenylethene, carbazole and dimesitylboron moieties

In this paper, a new aggregation-induced emission (AIE)-active compound, 1,2-bis(4-(3,6-bis(dimesitylboranyl)-9H-carbazol-9-yl)phenyl)-1,2-diphenylethene (BBDCZPD), has been successfully synthesized. The building block of BBDCZPD comprises tetraphenylethene as the skeleton, carbazole as the hole-transporting moiety and dimesitylboron as the electron-transporting moiety. Its structure is fully characterized using elemental analysis, mass spectrometry and proton nuclear magnetic resonance spectroscopy. The thermal, electrochemical and photophysical properties of BBDCZPD are studied using thermal analysis, electrochemical methods, UV-vis absorption spectroscopy and fluorescence spectroscopy, respectively. The results show that BBDCZPD exhibits excellent thermal stability and electrochemical stability as well as AIE properties. Moreover, a multilayer organic light-emitting diode (OLED) device is fabricated by using BBDCZPD as the non-doped emitter which displays good electroluminescence performances with a turn-on voltage of 5.2 V, a maximum luminance of 5406 cd m−2 and a maximum luminance efficiency of 5.34 cd A−1. The electroluminescence properties of BBDCZPD demonstrate its potential application in OLEDs.

Aggregation-enhanced emission and through-space conjugation of tetraarylethanes and folded tetraarylethenes

Aggregation-induced emission luminogens (AIEgens) are attracting rapidly increasing interest, due to their promising applications in various research frontiers. Tetraarylethenes are the most extensively studied AIEgens, which are usually prepared by McMurry couplings. In this study, we prepare not only new folded tetraarylethenes, but also tetraarylethanes by the McMurry coupling of different diarylmethanones. Moreover, the crystal structures, photophysical properties, orbital distributions, thermal stabilities and electrochemical behaviors of tetraarylethanes and folded tetraarylethenes are investigated. The new luminogens show through-space conjugation and aggregation-enhanced emission with high solid-state emission efficiencies approaching unity. Non-doped OLEDs based on the folded tetraarylethenes are fabricated, which perform well, affording high luminance up to 49 030 cd m−2 and good electroluminescence efficiencies of 6.6 cd A−1 and 2.5%.