Peng Junbiao

Photovoltaic Cells with TiO2 Nanocrystals and Conjugated Polymer Composites

Various compositional photovoltaic cells based on the blend of poly(3-hexylthiophene) (P3HT) as donors and TiO2 nanocrystals as acceptors are fabricated and investigated. It is demonstrated that the blend ratio of P3HT and TiO2 nanocrystals could greatly influence the performance of the photovoltaic cells. The maximum of 0.411% in power conversion efficiency under AM 1.5, 100mW/cm2, and 44.4% of fill factor are obtained in the solar cell with the blend weight ratio 1:1 of P3HT and TiO2 nanocrystals. The function of nanocrystal composition is discussed in terms of the results of photoluminescence spectroscopy, atomic force microscopy, transmission electron microscopy, and charge transport I–V curve.

Annealed Treatment Effect in Poly(3-hexylthiophene):Methanofullerene Solar Cells

Polymer photovoltaic devices based on poly(3-hexylthiophene) (P3HT) : [6,6]-phenyl-C61-butyricacid methyl ester (PCBM) 1:1 weight-ratio blend are reported. The effects of various annealing treatments on the device performance are investigated. Thermal annealing shows significant improvement of the device performances. For devices at 130°C annealing, maximum power conversion efficiency (PCE) of 3.3% and fill factor up to 60.3% is achieved under air mass 1.5, 100 mW/cm2 illumination. We discuss the effect of thermal annealing by the results of ultraviolet-visible absorption spectroscopy (UV-vis), dark current-voltage curve, atomic force microscopy (AFM).

Self-organization effect in poly(3-hexylthiophene): methanofullerenes solar cells

This paper studies the self-organization of the polymer in solar cells based on poly(3-hexylthiophene): [6, 6]-phenyl C61-butyric acid methyl ester by controlling the growth rate of active layer. These blend films are characterized by UV-vis absorption spectroscopy, charge-transport dark J – V curve, x-ray diffraction pattern curve, and atomic force microscopy. The results indicate that slowing down the drying process of the wet films leads to an enhanced self-organization, which causes an increased hole transport. Increased incident light absorption, higher carrier mobility, and balanced carrier transport in the active layer explain the enhancement in the device performance, the power conversion efficiency of 3.43% and fill factor up to 64.6% are achieved under Air Mass 1.5, 100 mW/cm2.

Full-color quantum dots active matrix display fabricated by ink-jet printing

Making full-color active matrix display based on quantum dot light emitting diodes (AM-QLEDs) via ink-jet printing is attractive in display industry due to QLEDs’ wide color gamut and their potential manufacturing advantages of large screen size and low cost. The challenges for realizing AM-QLED display are how to achieve high quality films through ink-jet printing, multi-color patterning, electroluminescence (EL) color purity, and high efficiency. Herein, a 2-inch diagonal full-color AM-QLEDs display with pixel density of 120 pixels per inch (PPI) fabricated by ink-jet printing technique is presented. Driven by a metal oxide TFT (MOTFT) back-panel, the display exhibits a maximum brightness of 400 cd m−2, and a color gamut of 109% (NTSC 1931). The red, green, and blue (RGB) monochrome QLEDs passive matrix panels fabricated by ink-jet printing technique have a current efficiency (CE) of 2.5, 13.9, and 0.30 cd A−1, respectively. To the best of our knowledge, the efficiencies are the highest among passive matrix QLEDs panels made by ink-jet printing technique. The ink-jet printed QDs films show good thickness uniformity due to high viscosity and low volatility of the printable inks, and no cross-contamination between adjacent pixels resulting from the hydrophobic pixel defining layer.

Efficient Polymer White-Light-Emitting Devices Based on Two Complementary Phosphorescent Colors

White polymer light-emitting diodes(WPLEDs) were fabricated by spin coating method using two complementary colors.The device structure used here is ITO/PEDOT(40 nm)/emitting layer(80 nm)/Ba(4 nm)/Al(120 nm).When the mass ratio of PVK:OXD-7:iridium bis(2-(4,6-difluorophenyl)-pyridinato-N,C2)picolinate(Firpic):tris(3-(2,6-dimethylphenoxy)-6-(thiophen-2-yl)pyridazine)iridium(Fs-1) was 63:27:10:0.25,white light with Commission Internationale de L′Eclairage(CIE) coordinates of(0.30,0.39) was obtained.The maximum current efficiency was 10.8 cd.A-1 and the maximum brightness was 4200 cd.m-2.To improve the hole-electron injection balance and the device′s character,a thin layer of water-soluble electronic transporting material was used to modify the cathode.In this case,efficient white light emission with a maximum current efficiency of 13.1 cd.A-1 and a maximum brightness of 6069 cd.m-2 was obtained.Using poly[(9,9-bis(3′-(N,N-dimethylamino) propyl)-2,7-fuorene)-alt-2,7-(9,9-dioctylfuorene)](PFN)(20 nm)/Al(120 nm) as the cathode resulted in CIE coordinates of(0.33,0.39) and the EL spectrum was also found to be quite stable.The effects of charge trapping and energy transfer on device performance were discussed by considering the photoluminescence(PL) and electroluminescence(EL) spectra as well as the energyband diagram of the device.

Research progress of active matrix organic light emitting diode (AMOLED) displays driven by metal oxide thin film transistors (TFT)

Metal oxide thin film transistors (MOTFTs) have been attracting great attention, because TFT technology are suitable for the requirement of novel display technology such as high definition, large screen liquid crystal display (LCD) and active matrix organic light emitting diode (AMOLED) display, with their high mobility, good uniformity, simple process, low process temperature, and low cost. In this article, material, device structure, fabricating process and application of MOTFT are introduced, and factors that influence MOTFT performance have been discussed. We developed a new class of metal oxide materials, which has a highest mobility of 35 cm2/Vs, threshold voltage of 1.63 V, current on/off ratio of 109, and sub threshold swing of 0.21 V/decade. Based on our MOTFT panel, we have developed a first 3~5 inch color AMOLED screen, transparent AMOLED, and flexible AMOLED. This novel MOTFT panel has a booming future in novel display such as TFT-LCD and AMOLED.

A new poly-Si TFT compensation pixel circuit employing AC driving mode for AMOLED displays

This paper presents a new poly-Si pixel circuit employing AC driving mode for active matrix organic light-emitting diode (AMOLED) displays. The proposed pixel circuit, which consists of one driving thin-film transistor (TFT), three switching TFTs, and one storage capacitor, can effectively compensate for the threshold voltage variation in poly-Si and the OLED degradation. As there is no light emission, except for during the emitting period, and a small number of devices used in the proposed pixel circuit, a high contrast ratio and a high pixel aperture ratio can be easily achieved. Simulation results by SMART-SPICE software show that the non-uniformity of the OLED current for the proposed pixel circuit is significantly decreased (< 10%) with an average value of 2.63%, while that of the conventional 2T1C is 103%. Thus the brightness uniformity of AMOLED displays can be improved by using the proposed pixel circuit.

Synthesis and Electroluminescent Properties of Phenyl-Substituted Poly(phenylenevinylene)

Poly(phenylenevinylene) (PPV) is one of the most efficient electroluminescent conjugated polymers and has the potential to be commercialized as important components in full-color flat panel displays. Here, we report an alternative synthetic route to the commercially available PPV derivative Super Yellow PPV (SY PPV) using 2-bromo-1,4-xylylene diacetate as a novel starting material. The intermediates, monomers, and the polymer were fully characterized by nuclear magnetic resonance (NMR) and elemental analysis. The SY PPV film shows an absorption maximum at 434 nm and an absorption onset at 510 nm with an optical bandgap of ca 2.44 eV. The photoluminescent and electroluminescent maximum of SY PPV are around 516 and 552 nm, respectively. The SY PPV obtained via this new synthetic route exhibits improved electroluminescent properties, a turn on voltage of over 2.4 V, a luminance maximum exceeding 49000 cd·m-2, and a maximum luminous efficiency (LE) of 21 cd·A-1 compared with the SY PPV prepared by the traditional route (16-18 cd·A-1).

Improved Performance of Polymer Light-Emitting Diodes with an Electron Transport Emitter by Post-Annealing

The enhancement of electroluminescent (EL) performance of polymer light emitting diodes (PLEDs) with electron transport emitter poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT) through thermal annealing treatment is investigated. Post-annealing of the PLEDs at temperature 120°C over the glass transition temperature of F8BT (99°C) could bring about an improvement of EL efficiency to more than twice that of the untreated devices, up to 6.02 cd/A. The improvement of the EL efficiency is due to the balance of electron and hole carriers in the exciton recombination zone, because the dominative electron current in the PLEDs could be reduced by post-annealing in terms of both issues of electron transport limited in the F8BT film and electron injection decreased by the interface between F8BT/cathode.

Efficient polymer light-emitting diodes with violet blue emission based on blends of PSiF6-PPP and PSiFC6C6

Efficient polymer light-emitting diodes (PLEDs) with violet blue emission were fabricated using blends of copolymers of paraphenylene-cosilafluorene (PSiF6-PPP) and polymer of poly (9,9′-alkyl-3,6-silafluorene) (PSiFC6C6). The performances of the devices are sensitive to the blend ratio. When the mass ratio of PSiF6-PPP to PSiFC6C6 is 1: 3, the highest external quantum efficiency is 1.96% at luminance of 105 cd · m−2, its electroluminescent (EL) spectrum peaks at 398 nm and full width at half maximum is 67 nm. The improvements of the device performances were due to the energy transfer from PSiFC6C6 to PSiF6-PPP and the balanced injection of electrons and holes.