An organic optocoupler(OOC)is fabricated with a tandem organic light-emitting diode(OLED)as the light source(input unit)and an organic photodiode(OPD)as the detector(output unit).It is found that using the tandem OLED as the input unit can significantly increase the current transfer ratio of the organic optocoupler.When the tandem OLED operates under 8 V and the OPD operates under-4 V,the current transfer ratio of the optocoupler reaches 5.4%.Simultaneously,the I_(ON)/I_(OFF) ratio of the optocoupler reaches 10^(5),which can be attributed to the small leakage current of the OPD,and the high efficiency of the OPD and the tandem OLED.
The origin of magneto-conductance(MC)in tri-(8-hydroxyquinoline)-aluminum(Alq3)-based organic light emitting diodes is investigated.Our results clearly show that the generated MC is related to the singlet polaron pair dissociation.Further studies on the MC in an electron blocking layer N,N'-bis(lnaphthyl)-N,N'-diphenyl-l,l'-biphentl-4,4'-diamine(NPB)and a hole blocking layer 2,2',2"-(1,3,5-Benzinetriyl)-tris(1-phenyl-1-H-benzimidazole(TPBi)-based devices indicate that the holes reaching the cathode from the dissociation of singlet polaron pairs on Alq3 are the main cause of the MC generation.It is found that the MC can be significantly reduced by doping a red fluorescence dye DCJTB as a hole trapper in Alq3.
Frequency-dependent electrical transport properties of 4,4′,4″-tri(N-carbazolyl)-triphenylamine(TCTA)are analyzed by impedance spectroscopy(IS)as functions of bias and temperature.The Cole-Cole plot shows a single semicircle which indicates that the equivalent circuit can be designed as a single parallel resistor R_(p)and capacitor C_(p)network with a series resistance R_(s).The bulk capacitance C_(p)remains unchanged while the resistance R_(p)decreases along with bias voltage.Conduction mechanism matches well with the space-charge-limited current(SCLC)model with exponential trap charge distributions.The temperature-dependent impedance studies reveal the activation energy of 0.246eV with no phase change in the temperature range 220-320K.These results indicate that the IS method is applicable for organic semiconductors having a wide band gap.
Kumada chain-growth polycondensation (KCGP) is a novel method for the synthesis of well-defined conjugated polymers.Because the Ni-catalyst can transfer in an intramolecular process to the propagating chain end,the polymerization follows chain-growth mechanism.With this newly developed method,various conjugated polymers,such as polythiophenes,poly(p-phenylene) (PPP),polypyrrole (PPy),and polyfluorene with controlled molecular weights and relatively narrow polydispersities (PDIs),have been prepared.Especially,the polymerizations for poly(3-alkylthiophene)s (P3ATs),PPP,and PPy exhibited quasi-living characteristics,which allows preparing polymer brushes,fully-conjugated block copolymers,and macroinitiators and macro-reactants for the synthesis of rod-coil block copolymers.In the current review,the progress in this new area is summarized.
GENG YanHou1,HUANG Li1,2,WU ShuPeng1,2 & WANG FoSong1 1State Key Laboratory of Polymer Physics and Chemistry
