Liang Chun-Jun

Surface oxidation of vanadium dioxide films prepared by radio frequency magnetron sputtering

This paper reports that the thermochromic vanadium dioxide films were deposited on various transparent substrates by radio frequency magnetron sputtering, and then aged under circumstance for years. Samples were characterized with several different techniques such as x-ray diffraction, x-ray photoelectron spectroscopy, and Raman, when they were fresh from sputter chamber and aged after years, respectively, in order to determine their structure and composition. It finds that a small amount of sodium occurred on the surface of vanadium dioxide films, which was probably due to sodium ion diffusion from soda-lime glass when sputtering was performed at high substrate temperature. It also finds that aging for years significantly affected the nonstoichiometry of vanadium dioxide films, thus inducing much change in Raman modes.

Organic Light Emitting Diodes Using Doped Alq3 as the Hole-transport Layer

Effects of 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) doping on the hole conductivity of Alq3layer are measured. In the hole-only device of Alq3, the current densities increase in 1–3 orders of magnitude upon doping with F4TCNQ, suggesting that the doping can effectively enhance the hole-injection and hole-transport ability of Alq3. An organic light-emitting device using an F4TCNQ doped Alq3 layer as the hole-injection and hole-transport layer, and pristine Alq3 as the electron-transport and emitting layer is fabricated and characterized. Bright emission is achieved in the simple OLED with p-doped Alq3 as the hole-transport layer and the intrinsic Alq3 as the electron-transport and emitting layer. The emitting efficiency and brightness of the device are further improved by inserting a thin electron block layer to confine the carrier recombination zone in the middle of the organic layers.

Improved performance of organic light-emitting devices with 2-(4-biphenyl)-5-(4-butylphenyl)-1,3,4-oxadiazole

Abstract The use of 2-(4-biphenyl)-5-(4-butylphenyl)-1,3,4-oxadiazole (PBD) as an anode buffer layer in organic light-emitting devices (OLEDs) with a configuration of indum tin oxide/α-naphtylphenyliphenyl diamine/8-hydroxyquinoline aluminum/LiF/Al has been studied. With PBD buffer layer several angstroms thickness, the current efficiency increased and the stability of the device was improved. The results suggested that PBD is a promising anode buffer layer for OLEDs. After Compared it with the TiO 2 buffer layer, TiO 2 and PBD are good candidates for hole-injecting buffer layer. And PBD buffer layer shows better operational durability and life.

A Novel Buffer Layer of Alq3 in Organic Electroluminescent Devices

Inserting the Alq3 layer in the ITO/NPB interface as the buffer layer can improve the organic electroluminescent devices. The current density efficiency and power efficiency of the device with the Alq3 buffer layer rises to 6.5 cd/A and 1.21 m/W at the current density of 120 mA/cm2, respectively. The improvement is mostly attributed to the balance of the hole and the electron injections.

Polymer Light-Emitting Diode Using Conductive Polymer as the Anode Layer

The analysis based on series equivalent circuit indicates that the resistance of electrode layers is the major factor limiting the current density of polymer light-emitting diodes (PLEDs) at higher voltages. The conductivity of 790 S/cm for the PEDOT:PSS film is achieved by secondary doping. At a thickness of 240 nm, the sheet resistance of the polymer layer is 51 Ω/sq, which is comparable to that of ITO films. The current density and luminance of the PLEDs with the polymer anode layer is higher than the ITO anode device, suggesting that it is feasible to replace ITO anode with a highly conductive polymer in PLEDs.

Effect of Crystallinity of Fullerene Derivatives on Doping Density in the Organic Bulk Heterojunction Layer in Polymer Solar Cells

Polymer solar cells (PSCs) based on poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) are fabricated by using 1,8-diiodooctane (DIO) as a solvent additive to control the doping density of the PSCs. It is shown that the processing of DIO does not change the doping density of the P3HT phase, while it causes a dramatic reduction of the doping density of the PCBM phase, which decreases the doping density of the whole blend layer from 3.7 × 1016 cm−3 to 1.2 × 1016 cm−3. The reduction of the doping density in the PCBM phase originates from the increasing crystallinity of PCBM with DIO addition, and it leads to a decreasing doping density in the blend film and improves the short circuit current of the PSCs.

Exploring photocurrent output from donor/acceptor bulk-heterojunctions by monitoring exciton quenching

In this work, a series of polymer bulk-heterojunctions is fabricated based on the combinations of different donors (Ds) (P3HT and PCPDTBT) and acceptors (As) (PCBM, ICBA, and F8BT). Exciton quenching efficiencies of the D–A pairs are obtained in order to quantify charge-transfer between the donor and the acceptor via a modified approach developed in conjunction with experimental results of optical absorption and photoluminescence spectra. It is discovered that the exciton quenching efficiency in the combination of PCPDTBT:PCBM and P3HT:PCBM reaches 70% and over, but in PCPDTBT:ICBA it is about 12%. A relatively high ΔLUMOdonor−acceptor results in a relatively high exciton quenching efficiency, which is responsible for better charge separation. The results agreed well with the photocurrent effect of the heterojunction layers. The work offers a convenient way to predict a potentially promising photovoltaic material with a selected D–A pair.

Laminated Polymer Solar Cells with PEDOT:PSS Film as Anode

A prefabricated conductive polymer film of polymer poly(3,4-ethylenedioxy-thiophene):poly (styrene-sulfonate) (PEDOT:PSS) is developed and is used as the anode in an inverted polymer solar cell (PSC) through a lamination process. The geometry structure of the PSC is indium tin oxide/interface layer/P3HT:PCBM/PEDOT:PSS. The PEDOT:PSS electrode is 5 μm and the sheet resistance is 10Ω/sq. The device fabrication process is vacuum-free and extremely simple. Lithium carbonate (Li2CO3) and cesium carbonate (Cs2CO3) are used as the cathode interface layers, respectively, and the result shows that Li2CO3 can enhance the open-circuit voltage (Voc) and fill factor distinctly, and the power conversion efficiency (PCE) can reach 2.1%.

Optimization of a poly(p-phenylene benzobisoxazole)-based light-emitting device with a complex cathode structure

In this work, we report the preparation of a series of electroluminescent (EL) devices based on a high-performance polymer, poly(p-phenylene benzobisoxazole) (PBO), and their optoelectronic properties, which have been rarely explored. The device structure is optimised using a complex cathode structure of tris-(8-hydoxyquinoline) aluminium (Alq3)/LiF/Al. By tuning the thickness of the Alq3 layer, we improve the device efficiency dramatically in an optimized condition. Further analysis reveals that the Alq3 layer in the complex cathode structure acts as a hole blocker in addition to its electron-injection role. A green light emission with a maximum brightness of 8.7 ? 103 cd/m2 and a moderate current efficiency of 4.8 cd/A is obtained. These values are the highest ever reported for PBO devices. The high operational stability demonstrated by the present device makes it a promising tool for display and lighting applications. A new material is added to the selection of polymers used in this field up to now.

Towards Color Stable Three-band White Organic Light-emitting Diodes

White organic light-emitting diodes based on three small molecular fluorescence materials were designed and prepared.The emitting layers consisted of a red dye,4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetra-methyljulolidin-4-yl-vinyl)-4H-pyran(DCJTB),doped in a green layer of 8-hydroxyquinoline aluminum salt(Alq3),which further formed a heterojunction with a blue layer of 2,2′-(1,3-phenylene)-bis[5-(4-tert-butylphenyl)-1,3,4-oxadiazole](OXD-7).N,N′-bis-(naphthalene-1-yl)-N,N′-bis(phenyl)-benzidine(NPB) was used as a hole transport layer.Voltage dependent emission spectra and their colorimetric characteristics were manipulated using different device structures.After adjusting the carrier injection/transporting properties,the exciton recombination region was confined and the color stability was improved against the driving voltages.An improved white light-emitting device has a wide spectrum in visible range and a good color stability,its color coordinates change slightly from CIE(x,y)=(0.364,0.314) to CIE(x,y)=(0.332,0.291) when the driven voltage changes from 9.1 V to 12.9 V.