Bright electroluminescence from a conjugated dendrimer

Photoluminescence and electroluminescence (EL) from a conjugated dendrimer consisting of three distyrylbenzene units linked by a central nitrogen atom as core and meta-linked biphenyl units as dendrons were investigated. The conjugated dendrimer emits green light and shows photoluminescence quantum efficiency of 9%. Bright electroluminescence was realized by using bilayer devices with blurred interface, which were fabricated by sequentially spin coating a neat dendrimer and a dendrimer doped with 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD). The devices have the following structure: indium tin oxide/3,4-polyethylenedioxythiothene-polystyrenesulfonate/dendrimer/ dendrimer:PBD/Al. By optimizing the concentration of PBD, the maximum brightness and EL quantum efficiency reach 4100 cd/m(2) and 0.17%, respectively. This is the best result reported so far on organic light-emitting diodes using dendrimer as an active material with an Al cathode. (C) 2002 American Institute of Physics

Solution-processed blue/deep blue and white phosphorescent organic light emitting diodes (PhOLEDs) hosted by a polysiloxane derivative with pendant mCP (1, 3-bis(9-carbazolyl)benzene)

The synthesis and characterization is reported of an efficient polysiloxane derivative containing the 1,3-bis(9-carbazolyl)benzene (mCP) moiety as a pendant unit on the polysiloxane backbone. In comparison with mCP, the mCP-polysiloxane hybrid (PmCPSi) has significantly improved thermal and morphological stabilities with a high decomposition temperature (Td = 523 °C) and glass transition temperature (Tg = 194 °C). The silicon–oxygen linkage of PmCPSi prevents intermolecular π-stacking and ensures a high triplet energy level (ET = 3.0 eV). Using PmCPSi as a host, blue phosphorescent organic light emitting devices (PhOLEDs) effectively confine triplet excitons, with efficient energy transfer to the guest emitter and a relatively low turn-on voltage of 5.8 V. A maximum external quantum efficiency of 9.24% and maximum current efficiency of 18.93 cd/A are obtained. These values are higher than for directly analogous poly(vinylcarbazole) (PVK) based devices (6.76%, 12.29 cd/A). Good color stability over a range of operating voltages is observed. A two-component “warm-white” device with a maximum current efficiency of 10.4 cd/A is obtained using a blend of blue and orange phosphorescent emitters as dopants in PmCPSi host. These results demonstrate that well-designed polysiloxane derivatives are highly efficient hosts suitable for low-cost solution-processed PhOLEDs

Low-Bandgap Polymers for High-Performance Photodiodes with Maximal EQE near 1200 nm and Broad Spectral Response from 300 to 1700 nm

Polymer photodiodes with broad spectral response above 1500 nm can be used for imaging in the near-infrared window of the atmosphere. Three low-bandgap polymers based on 3,6-dithiophen-2-yl-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione (DPP), [1,2,5]thiadiazolo[3,4-g]quinoxaline (TQ), benzobisthiadiazole (BBT), and dithienopyrrole (DTP) are designed and synthesized. No-gain and gain polymer photodiodes with polymers:PC71BM as active layer materials and with aluminum doped ZnO nanoparticles:2,9-bis(3-(dimethylamino)propyl)anthra[2,1,9-def:6,5,10-d'e'f']diisoquinoline-1,3,8,10(2H,9H)-tetraone (AZO:PDIN), MoO3, and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) as interlayer materials are prepared. No-gain photodiodes based on polymer P1 exhibit the external quantum efficiency (EQE) of 7.8% at 1200 nm, which is among the best values of polymer photodiodes known to date. Gain photodiodes based on P1 and P3 also exhibit a maximal EQE near 1200 nm. In addition, gain photodiodes based on P1 have a specific detectivity over 1013 Jones in 300-1360 nm and spectral response in the region of 300-1700 nm

Low-LUMO acceptor polymers for high-gain all-polymer photodiodes

In this work, we report three acceptor polymers with low levels of lowest unoccupied molecular orbital (LUMO) energies and studies on all-polymer photodiodes. By employing these polymers as electron acceptors and PTB7-Th as electron donors, we prepared all-polymer photodiodes that exhibited a high gain in external quantum efficiency (EQE) and high detectivity. In particular, P3-based devices showed EQE over 40 000%, responsivity over 110 A W−1 and a specific detectivity of 3.5 × 1014 Jones, representing the best result of all-polymer photodiodes reported to date. Our work has demonstrated that high gain all-polymer photodiodes could be readily achieved by using appropriate interlayers and low-LUMO acceptor polymers

Low-Bandgap Terpolymers for High-Gain Photodiodes with High Detectivity and Responsivity from 300 nm to 1600 nm

Three strong electron-withdrawing monomers and one electron-donating monomer were chosen by design to impart some desirable properties to the target terpolymers (P1-P3) for use in the photodiodes, such as strong donor-acceptor charge transfer, low bandgap, high mobility and good film morphology. Photodiodes with a device structure of ITO/ZnO/active layer/BCP/Al exhibited a significant increase of EQE only under forward bias. In particular, the P2-based device had the specific detectivity greater than 1013 Jones from 330 nm to 1060 nm and 1011 Jones from 300 nm to 1600 nm under 0.5 V and linear dynamic range over 100 dB under 2.0 V. In comparison, after the UV light treatment to the ZnO layer, the P2-based photodiodes exhibited a high gain in photocurrent under both forward and reverse bias and had specific detectivity above 1013 Jones at 320–1140 nm, 1012 Jones at 300–1460 nm and 1011 Jones at 300–1600 nm under 0.5 V. Our wor

Effect of compositions of acceptor polymers on dark current and photocurrent of all-polymer bulk-heterojunction photodetectors

A series of electron-acceptor polymers, copolymers and blends were used in all-polymer BHJ photodetectors and the effect of acceptor compositions on the key device parameters of dark current density and photocurrent was investigated. Compared with acceptor polymers and polymer blends, the devices based on acceptor copolymer showed lowered dark current and higher photocurrent, due to optimal molecular stacking and morphology of the BHJ active layer. The acceptor blends tend to cause a large phase separation and rough surface of the active layer, thus leading to a low detectivity of the device. Among all the acceptor compositions studied in this work, the all-polymer BHJ photodetector based on a donor polymer (PolyD) and an acceptor copolymer (PolyAA′50) exhibited the highest specific detectivity of over 1012 Jones in the spectral region of 320–980 nm under −0.1 V bias

Fluorescence quenching and enhancement of vitrifiable oligofluorenes end-capped with tetraphenylethene

We report the synthesis of novel amorphous fluorene-based fluorophores that have been end-capped with tetraphenylethene (TPE). Although in the solid state the fluorophores show bright cyan fluorescence with high (68%) photoluminescence quantum efficiency (PLQE), strong fluorescence quenching is observed in solution with low PLQE values ranging from 0.3% to 2.1%. When the fluorophores were added to a 90% water-THF solvent mixture nanoparticles were formed, which was confirmed by Dynamic Light Scattering (DLS) and Atomic Force Microscopy (AFM). Subsequent fluorescence measurements reveal that all the fluorophores exhibit aggregation induced emission (AIE) with high PLQE (41%). We have carried out a comparative study of 5 fluorene-based TPE materials (F(1-5)TPE), in which the fluorene core is extended, and investigated their thermal, optical, electrochemical and electroluminescence properties. From fluorescence quantum yield data we have discovered that the AIE effect decreases as the fluorene core increases both in the nanoparticle and in the solid state. Thermal analysis reveals that all fluorophores are amorphous with high thermal stabilities. Potential application in solid state vapour sensing has been demonstrated using dichloromethane that shows "on" and "off" fluorescence behaviour. Finally, Organic Light Emitting Diodes (OLEDs) have been fabricated with device configuration ITO/PEDOT/F(1-5)TPE/TPBi/LiF/Al. The best OLED device that incorporates F1-TPE as the emitter exhibits a turn-on voltage of 5.8 V, L max = 1300 cd m -2, η P,max = 1 lm W -1 and η C,max = 2.6 cd A -1. © 2012 The Royal Society of Chemistry.Link_to_subscribed_fulltex

Side-chain engineering for fine-tuning of molecular packing and nanoscale blend morphology in polymer photodetectors

A series of four low-bandgap polymers containing diketopyrrolopyrrole (DPP) and dithienopyrrole (DTP) functionalized with four different side chains of 4-phenyl, 4-octylphenyl, 4-(octyloxy)phenyl and 4-(octylthio)phenyl were synthesized. Subtle changes in the side chains of polymers are found to effectively affect the molecular stacking and crystallinity, film morphology, and photodetector performance. The best polymer photodetector displays an average external quantum efficiency (EQE) of 40% and a specific detectivity (D∗) of over 1013 Jones in th