A charge carrier mobility of polymer films with the time-of-flight(TOF) technique using a fullerene layer was measured and the TOF photocurrent waveform can be remarkably improved.The 80-nm-thick fullerene layer is functioned as a charge-separation layer(CSL) which was placed between ITO electrode and the polymer layer of MEH-PPV(poly[2-methoxy-5-(2'-ethylhexyloxy) 1,4-phenylenevinylene]).In the CSL,the photo-generated holes and electrons can be efficiently separated,resulting in an enhanced current signal and great improvement of TOF waveform.The sample structure with fullerene layer exhibits a great advantage to measure the hole mobilities of polymers with low energy band gap.
A solution-processed zinc oxide (ZnO) thin film as an electron collection layer for polymer solar cells (PSCs) with an inverted device structure was investigated. Power conversion efficiencies (PCEs) of PSCs made with a blend of poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) are 3.50% and 1.21% for PSCs with and without the ZnO thin film, respectively. Light intensity dependence of the photocurrent and the capacitance-voltage measurement demonstrate that the increased PCEs are due to the restriction of the strong bimolecular recombination in the interface when a thin ZnO layer is inserted between the polymer active layer and the ITO electrode. These results demonstrate that the ZnO thin film plays an important role in the performance of PSCs with an inverted device structure.
YANG TingBinQIN DongHuanLAN LinFengHUANG WenBoGONG XiongPENG JunBiaoCAO Yong
High-brightness and color-stable two-wavelength hybrid white organic light emitting diodes （HWOLEDs） with the configuration of indium tin oxide （ITO）/ N, N, N, N-tetrakis（4-methoxyphenyl）-benzidine （MeO-TPD）： tetrafluoro-tetracyanoqino dimethane （F4-TCNQ）/N,N-di（naphthalene-1-yl）-N,N-diphenyl-benzidine （NPB）/ 4,4-N,N-dicarbazolebiphenyl （CBP）： iridium （III） diazine complexes （MPPZ） 2 Ir（acac）/NPB/2-methyl-9,10-di（2-naphthyl）anthracene （MADN）： p-bis（p-N,N-di-phenyl-aminostyryl）benzene （DSA-ph）/bis（10-hydroxybenzo[h] quino-linato）beryllium complex （Bebq2）/LiF/Al have been fabricated and characterized. The optimal brightness of the device is 69932 cd/m2 at a voltage of 13 V, and the Commission Internationale de l’Eclairage （CIE） chromaticity coordinates are almost constant during a large voltage change of 6–12 V. Furthermore, a current efficiency of 15.3 cd/A at an illumination-relevant brightness of 1000 cd/m2 is obtained, which rolls off slightly to 13.0 cd/A at an ultra high brightness of 50000 cd/m2. We attribute this great performance to wisely selecting an appropriate spacer together with effectively utilizing the combinations of exciton-harvested orange-phosphorescence/blue-fluorescence in the device. Undoubtedly, this is one of the most exciting results in two-wavelength HWOLEDs up to now.
Several highly efficient iridium-complex polymer light-emitting devices （PLEDs） are fabricated, with a newly synthesized blue conjugated polymer, poly[（9,9-bis（4-（2-ethylhexyloxy）phenyl）-fluorene）-co-（3,7-dibenziothiene-S,S- dioxide15）] （PPF-3,TSO15）, chosen as host. High luminous efficiencies of 7.4 cd.A-1 and 27.4 cd.A-1 are achieved in red and green PLEDs, respectively, by optimizing the doping concentrations of red phosphorescent dye iridium bis（1- phenylisoquinoline） （acetylacetonate） （Ir（piq）） and green phosphorescent dye iridium tris（2-（4-tolyl）pyridinato-N, C2＇） （Ir（mppy）3）.Furthermore, highly efficient white PLEDs （WPLEDs） with the Commission Internationale de l＇Eclairage （CIE） coordinates of （0.35, 0.38） are successfully produced by carefully controlling the doping concentration of the irid- ium complex. The obtained WPLEDs show maximal efficiencies of 14.4 cd.A-1 and 10.1 lm.W-1, which are comparable to those of incandescent bulbs. Moreover, the electroluminescent spectrum of the white device with an initial luminance of about 1000 cd.m-2 is stable, subject to constant applied current stress, indicating that good device stability can be obtained in this system.
Efficient white light emitting polymers were synthesized based on poly（9,9-dioctylfluorene-co-dibenzothiophene- S,S-dioxide） as blue emitter and a bisphenylamine functionalized 2,1,3-benzothiadiazole （DPABT） as red emitter. It was found that the incorporation of hole-transporting carbazole moiety into polymer main chain could effectively reduce the hole injection barriers, which can lead to distinctly improved charge balance in the emissive layer. Additionally, the hole- transporting carbazole units may form efficient bipolar host with electron-transporting dibenzothiophene-S,S-dioxide units. The white light emitting diodes based on single polymer PFSOCzDPABT showed the maximum luminous efficiency of 3.3 cd/A with the maximum luminance of 10282 cd/m2, and the luminous efficiency showed only 24% roll off at current density of 400 mA/cm2. These Commission Internationale d＇Enclairage （CIE） coordinates of the devices changed slightly with the driving voltages increasing from 8 V to 12 V, and were very close to National Television System Committee （NTSC） standard white light emission of （0.33, 0.33）. The results indicated that the incorporating bipolar host and low band gap DPABT unit was a promising way to achieve efficient single white light emitting copolymers.
Lei YingYan-hu LiCai-hong WeiMin-quan Wang杨伟Hong-bin WuYong Cao
