Shanghui Ye

Solution-processed efficient deep-blue fluorescent organic light-emitting diodes based on novel 9,10-diphenyl-anthracene derivatives

A series of 9,10-diphenyl-anthracene derivatives bearing either benzimidazole or carbazole moieties as substituents were synthesized and characterized as blue emitters for organic light-emitting diodes (OLEDs). Their optical, electrochemical and thermal properties have been investigated, and their molecular structure–property relationships were evaluated. These compounds both exhibited a high glass-transition temperature (Tg ≥ 195 °C) and a high decomposition temperature (Td ≥ 494 °C). The solution processed non-doped device using CAC as a fluorescence emitter showed a maximum luminance efficiency of 1.63 cd A−1, a maximum power efficiency of 0.77 lm W−1 and a maximum external quantum efficiency of 1.53%. By introducing 1,3-bis[4-tert-butylphenyl-1,3,4-oxadiazolyl] phenylene (OXD-7):polyvinylcarbazole (PVK) as host in the emitting layer, the doped deep-blue emitting device of CAC exhibited a turn-on voltage of 4.75 V, a maximum luminance efficiency of 3.03 cd A−1, a maximum power efficiency of 1.64 lm W−1 and a maximum external quantum efficiency of 2.81%. Our results demonstrate a promising approach to well-designed materials for use in deep-blue fluorescence OLED applications.

High Power Efficiency Solution-Processed Blue Phosphorescent Organic Light-Emitting Diodes Using Exciplex-Type Host with a Turn-on Voltage Approaching the Theoretical Limit.

Three solution-processable exciplex-type host materials were successfully designed and characterized by equal molar blending hole transporting molecules with a newly synthesized electron transporting material, which possesses high thermal stability and good film-forming ability through a spin-coating technique. The excited-state dynamics and the structure-property relationships were systematically investigated. By gradually deepening the highest occupied molecular orbital (HOMO) level of electron-donating components, the triplet energy of exciplex hosts were increased from 2.64 to 3.10 eV. Low temperature phosphorescence spectra demonstrated that the excessively high triplet energy of exciplex would induce a serious energy leakage from the complex state to the constituting molecule. Furthermore, the low energy electromer state, which only exists under the electroexcitation, was found as another possible channel for energy loss in exciplex-based phosphorescent organic light-emitting diodes (OLEDs). In particular, as quenching of the exciplex-state and the triplet exciton were largely eliminated, solution-processed blue phosphorescence OLEDs using the exciplex-type host achieved an extremely low turn-on voltage of 2.7 eV and record-high power efficiency of 22.5 lm W(-1), which were among the highest values in the devices with identical structure.

Solution processable low bandgap thienoisoindigo-based small molecules for organic electronic devices

Two donor–acceptor conjugated small molecules that consist of thienoisoindigo as an acceptor unit and benzofuran or naphthalene as a donor building block have been synthesized via a Suzuki coupling reaction. The small molecules, TII(BFu)2 and TII(Na)2, exhibit broad and near-infrared absorption in the range of 500–900 nm while their absorption maxima locate at around 620 nm in films. Optical band gaps calculated from the solid state absorption cutoff value are 1.49 eV for TII(BFu)2 and 1.53 eV for TII(Na)2, respectively. These small molecules possess p-channel charge transport characteristics when used as the active semiconductor in organic thin-film transistors (OFETs). The highest hole mobilities of 1.28 × 10−3 cm2 V−1 s−1 for TII(BFu)2 and 1.29 × 10−3 cm2 V−1 s−1 for TII(Na)2 have been achieved in top-contact-bottom-gate OFET devices. The preliminary characterization of bulk heterojunction photovoltaic devices consisting of small molecules and PC71BM yield power conversion efficiencies (PCE) of 1.24% for TII(BFu)2 and 1.04% for TII(Na)2. Moreover, the relationships between the semiconductor devices performance and film morphology, and energy levels are discussed.

A dithienyl benzotriazole-based poly(2,7-carbazole) for field-effect transistors and efficient light-emitting diodes

In this work, a donor–acceptor type copolymer, poly[(N-9′-heptadecanyl-2,7-carbazole)-alt-(4,7-bis(2′-thienyl)-2-dodecyl-2,1,3-benzotriazole)] (PCDTBTz) is introduced for versatile applications in organic electronics. PCDTBTz exhibits excellent solubility, film-forming ability and morphological stability, along with charming optoelectronic properties. The solution processable OFET device displays typical p-type transporting characteristics with a moderate mobility up to 4.3 × 10−4 cm2/V·s upon thermal annealing at 80 °C, and PLEDs in the device structure of ITO/PEDOT:PSS (10 nm)/Poly-TPD (30 nm)/PCDTBTz (32 nm)/Alq3 (40 nm)/Ca:Ag show a bright orange red emission with a maximum brightness of 13 655 cd/m2 at 1607.9 mA/cm2 and 12.6 V, and a maximum EL efficiency of 0.85 cd/A. All the results indicate that PCDTBTz is a promising candidate for optoelectronic materials used in both for polymer FETs and LEDs.

High-brightness solution-processed phosphorescent OLEDs with pyrimidine-based iridium(III) complexes

Two heteroleptic cyclometalated iridium(III) complexes, Ir(ppm)2(pic) and Ir(ppm)2(taz), using 4,6-diphenyl pyrimidine (Hppm) as a cyclometalating ligand, were successfully synthesized and characterized. Strong emission at 555 and 532 nm with high photoluminescence quantum yields of 83% and 86% in PMMA at 298 k were obtained for Ir(ppm)2(pic) and Ir(ppm)2(taz), respectively. Solution-processed organic light-emitting diodes (OLEDs) based on Ir(ppm)2(pic) and Ir(ppm)2(taz) showed high-brightness of 112 233 and 125 072 cd m−2, peak current efficiencies of 30.6 and 40.4 cd A−1 and maximum external quantum efficiencies of 10.4 and 17.3%, respectively, accompanied by very low efficiency roll-off values. The ancillary ligand taz tuned the emission to saturated green, and more importantly, it can significantly increase the spectral stability and device efficiency.

Solution-processable small molecule semiconductors based on pyrene-fused bisimidazole and influence of alkyl side-chain on the charge transport

To explore the potential of pyrene-fused biimidazole as a building block for soluble small molecule semiconductors, we designed and synthesized PBI-L-Na and PBI-B-Na. Imidazole rings provided substitution positions for the solubilising groups at the K-region, however, DFT calculations revealed that the repulsive steric hindrance from the neighboring hydrogen atoms on pyrene forced alkyl side chains into a twisted conformation. Thus, side chains on this type of molecule exerted a prominent influence on the molecular packing and affected their optoelectronic properties intensively in the solid state. PBI-L-Na exhibited a more ordered packing of the large conjugated plane with a π–π stacking distance of 0.36 nm and showed a hole mobility up to 0.12 cm2 V−1 s−1. Bulkier branched chains provided better solubility but impeded molecular packing of PBI-B-Na, thus giving a hole mobility of 4.6 × 10−3 cm2 V−1 s−1.

Highly efficient orange phosphorescent organic light-emitting diodes based on an iridium(III) complex with diethyldithiocarbamate (S^S) as the ancillary ligand

A novel iridium(III) complex Ir(dpp)2(dta) (dppH = 4,6-diphenyl pyrimidine; dta = diethyldithiocarbamate) was synthesized and characterized. The complex displayed strong emissions at 575 nm with high photoluminescence quantum yields of 86% in the doped poly(methyl methacrylate) (PMMA) film at 1% doping concentration. The orange-yellow polymer light-emitting devices (PLEDs) based on Ir(dpp)2(dta) as a triplet emitter with different concentrations (x = 1%, 3%, 5%, 7% and 10%) doped in a polymeric host 70% poly(N-vinylcarbazole) (PVK) + 30% 2,2′-(1,3-phenylene)bis[5-(4-tert-butylphenyl)-1,3,4-oxadiazole] (OXD-7) were fabricated with high luminance and efficiency. The device achieved an ideal turn-on voltage (<4 V) and superior luminance (81 918 cd m−2) as well as electroluminescence efficiency (30.12 cd A−1) at 3% doping concentration.

Thienoisoindigo-Based Polymers Bearing Diethynylbenzene and Diethynylanthracene Units for Thin Film Transistors and Solar Cells

Two thienoisoindigo-based donor-acceptor conjugated polymers were synthesized via Sonogashira coupling reaction with 1,4-diethynylbenzene (P(TII-BEN)) and 9,10-diethynylanthracene (P(TII-ANT)) as donor units, respectively. The optical and electrochemical properties of the polymers were also investigated. The highest hole mobility were 4.38 × 10-3 cm2 V-1 s-1 for P(TII-BEN) and 9.40 × 10-3 cm2 V-1 s-1 for P(TII-ANT) in bottom-gated/top-contact field-effect transistors. The bulk heterojunction organic solar cells consisting of the polymers and PC71BM yielded power conversion efficiencies of 1.59% for P(TII-BEN) and 1.90% for P(TII-ANT). Moreover, the microstructures were investigated by X-ray diffraction and atomic force microscopy.