Zhang Zhi-lin

The effect of rubrene as a dopant on the efficiency and stability of organic thin film electroluminescent devices

Rubrene was doped into the hole transport layer of an organic thin film electroluminescent (OTFEL) device with a double-layered structure. It was found that the dopant has a profound influence on the EL characteristics - it changed the region of light emission, increased the luminescence efficiency by more than 50% and improved the device stability tenfold. The reasons for these effects are discussed based on injection theory and the energy level diagram of the device.

Energy transfer and white emitting organic thin film electroluminescence

Abstract Energy transfer between in N , N ′-bis-(1-naphthyl)- N , N ′-diphenyl-1,1′-biphenyl-4-4′-diamine (NPB) and rubrene was investigated. The device ITO/CuPc/NPB:rubrene/blocking layer /Alq/MgAg, in which copper phthalocyanine (CuPc) is used as buffer layer, NPB as the hole transporting layer (HTL), trimer of N -arylbenzimidazoles (TPBi) [or 2–(4–biphenylyl)–5–(4–tertbutylphenyl)–1,2,3–oxadiazole(PBD) or 1,2,4–triazolederivative(TAZ)] as the blocking layer, Tris(8-quinolinolato)aluminum complex (Alq) as electron transporting layers (ETL), can not give white emitting light. White emitting light can be realized in a new device with the structure ITO/CuPc/NPB/blocking layer:rubrene/Alq/MgAg, in which rubrene is doped in blocking layer instead of in NPB. The emission spectrum of this device covers a wide range of visible region and can be adjusted by the concentration of rubrene. The white emitting devices with CIE coordinates x =0.31, y =0.32, maximum luminance 8635 cd/m 2 and luminous efficiency 1.39 Lm/w, were obtained with the blocking layer TPBi doped with 1.5% rubrene.

Organic thin film electroluminescent devices with ZnO:Al as the anode

Some organic thin film electroluminescent (EL) devices with aluminium-doped zinc oxide as the hole-injecting electrode have now been manufactured. Their EL spectra and J - V and B - V characteristics have been studied in detail. The work function and ionization potential of the materials composing the devices have been measured and their energy models given. The EL performance properties have been explained well.

Investigation on SnS film by RF sputtering for photovoltaic application

Tin sulfide (SnS) solar cell semiconductor thin films were prepared by an RF sputtering method. The component, crystal structure, optical properties and electrical properties of SnS films were measured. The relationship between the SnS films properties and the sputtering condition was discussed. Using Sb as a dopant and combining thermal annealing at elevated temperatures (about 400/spl deg/C), n-type SnS homojunction solar cell thin films were obtained.

Estimation of electron mobility of n-doped 4, 7-diphenyl-1, 10-phenanthroline using space-charge-limited currents

The electron mobilities of 4, 7-diphenyl-1, 10-phenanthroline (BPhen) doped 8-hydroxyquinolinatolithium (Liq) at various thicknesses (50–300 nm) have been estimated by using space-charge-limited current measurements. It is observed that the electron mobility of 33 wt% Liq doped BPhen approaches its true value when the thickness is more than 200 nm. The electron mobility of 33 wt% Liq doped BPhen at 300 nm is found to be ~5.2 × 10−3 cm2/(V·s) (at 0.3 MV/cm) with weak dependence on electric field, which is about one order of magnitude higher than that of pristine BPhen (3.4 × 10−4 cm2/(V·s)) measured by SCLC. For the typical thickness of organic light-emitting devices, the electron mobility of doped BPhen is also investigated.

Improving Stability of Organic Electroluminescent Diode by Inserting Copper Phthalocyanine Between the Anode and Hole Transport Layer

Copper phthalocyanine(CuPc) thin film layer was inserted between the anode indium tin oxide and the hole transport layer TPD of an organic thin film electroluminescent device with a double-layered structure. It is found that the CuPc layer greatly improves the device stability. The durability of the device with CuPc layer increases about 8 times. The fact that at a constant current density the driving voltage remains unchanged with operation time for the device with CuPc layer means that the barriers of the carriers injection are stable due to the inserted CuPc layer.

Organic thin film transistors with PMMA modified insulator

A double insulation layer structure organic thin films transistor (OTFT) was investigated for improving the performance of the SiO2 gate insulator. A 50 nm PMMA layer was coated on top of the SiO2 gate insulator as the organic insulator layer. The results demonstrated that using inorganic/organic compound insulator as the gate dielectric layer is an effective method to fabricate OTFTs with improved electric characteristics and decreased leakage current. Electrical parameters of carrier mobility and on/off ratio were calculated. OTFT based on Si substrate with a field-effect mobility of 4.0 × 10−3 cm2/Vs and on/off ratio of 104 was obtained.

Effects of microcavities on the spontaneous emission of organic light-emitting diodes with ZnO:Al as the anode

Organic light-emitting diodes (LED) with a microcavity structure and an aluminium-doped zinc oxide ZnO:Al (AZO) anode have been fabricated. Effects of microcavities on the spontaneous emission of the organic LED, such as spectral narrowing, intensity enhancement and angle dependence of the emission, have been observed. Different emission colours have been obtained by changing the thickness of the AZO layer and that of a filler layer. The wavelengths of the cavity modes can be explained on the basis of the calculated total optical thickness of the individual cavities.

Optimizing structure for constructing a highly efficient inverted top-emitting organic light-emitting diode with stable electroluminescent spectra

We demonstrate a highly efficient inverted top-emitting organic light-emitting diode (TOLED) having stable electroluminescent spectra and color coordination with variation of viewing angles by simply tuning the resonance wavelength corresponding to the free emission of the emitter. Using a doped fluorescent emitting system, the inverted TOLED exhibits an enhanced maximum current efficiency of 19 cd/A and a power efficiency of 17 lm/W, which are much higher than those (11 cd/A and 5 lm/W) of the counterpart with normal structure, although both TOLEDs behave with similar stable electroluminescent spectra characteristics. The results indicate that we provide a simple and effective method of constructing an excellent inverted TOLED for potentially practical applications.

Bit-panel to realize gray-scale control of synchronous VGA display by passive OLED matrix

A bit-panel-plus-weight method has been proposed to realize gray-scale control of synchronous VGA display by passive matrix OLED. The presented VGA controller has been fabricated by FPGAs and can achieve a better result of gray-scale control by a 96*64 PMOLED panel.