ABSTRACT
This paper introduces the methods improving the performance and stability of copper-phthalocyanine(CuPc) / fullerene (C60) small molecule solar cells by using tris-(8-hydroxyquinoline) aluminum(Alq3): cesium fluoride(CsF) composite cathode buffer layer. The device with Alq3:CsF composite cathode buffer layer with a 4 wt. % CsF at a thickness of 5 nm exhibits a power conversion efficiency (PCE) of up to 0.76%, which is an improvement of 49%, compared to a device with single Alq3 cathode buffer layer and half-lifetime of the cell in air at ambient circumstance without any encapsulation is almost 9.8 hours, 6 times higher than that of without buffer layer, so the stability is maintained. The main reason of the device performance improvement is that doping of CsF can adjust the interface energy alignment, optimize the electronic transmission characteristics of Alq3 and improve the short circuit current and the fill factor of the device using ultraviolet-visible absorption, external quantum efficiency and single-electron devices. Placed composite cathode buffer layer devices with different time in the air, by comparing and analyzing current voltage curve, Alq3:CsF can maintain a good stability as Alq3. Alq3:CsF layer can block the diffusion of oxygen and moisture so completely as to improve the lifetime of the device.
ABSTRACT
In the present work, the photoluminescence (PL) and electroluminescence (EL) characteristics of Tris[2-(2,4-difluorophenyl)pyridine]iridium(III) (Ir(Fppy)3) doped poly(n-vinylcarbazole) (PVK) with different doping concentrations were investigated. And a blue phosphorescent organic light-emitting diode (OLED) with the structures of ITO/PEDOT : PSS/PVK : Ir(Fppy)3/BCP/Alq3/LiF/Al was fabricated. The experimental results show that the luminescence performances of devices are different as the doping concentration of Ir(Fppy)3 is different. When the doping concentration of Ir(Fppy)3 is lower, the luminescence of PVK can be found in EL spectra. When the doping concentration is too high, concentration quenching may occur. As the doping concentration is suitable, the luminescence of PVK can not be found, only the luminescence of Ir(Fppy)3 can be found in EL spectra. It is concluded that the device with doping concentration of 4% has the best photoelectric performance according to its current density-voltage-luminance curve.
ABSTRACT
The present work investigates the effects of different buffer layers on the performance of blue organic light-emitting diodes (OLEDs), and compares them with the device with no buffer layer. Two kinds of blue OLEDs with 4,4'-bis(2,2'-diphenyl vinyl)-1,1'-biphenyl (DPVBi) as the emitting layer, N, N'-bis-(1-naphthyl)-N, N'-1-diphenyl-1,1 '-biphenyl-4, 4'-diamine (NPB) as the hole transporting layer, and copper phthalocyanine (CuPc) and poly(3,4-ethylenedioxythiophene) : poly (styrenesulphonate) PEDOT : PSS as the hole injection layer respectively were fabricated with the structures of ITO/CuPc/NPB/DPVBi/BCP/Alq3 /Al and ITO/PEDOT : PSS/NPB/DPVBi/BCP/Alq3/Al. Moreover, the effects of different preparation technology of CuPc on the performance of OLEDs were also investigated. It was found that the performance of the devices with a hole injection layer is better than that of the device without any hole-injection layer. Although the luminance and efficiency of the water-soluble CuPc based device are worse than that of the device with thermally evaporated CuPc, but better than that of the device with water-soluble PEDOT : PSS. So the water-soluble CuPc is a good hole injection material because it is easier to fabricate the film than traditional CuPc.
ABSTRACT
The present work investigates the photoluminescence (PL) and electroluminescence (EL) characteristics of Eu-complex Eu (UVA)3Phen doped PVK with different doping concentrations. The results indicate that there exists Forster energy transfer from PVK to Eu(UVA)3 phen in the mixed system. It can get good color purity by optimizing the doping concentration of host and guest materials. And the authors can obtain the best doping concentration to be 4% in EL device.
ABSTRACT
The growth mechanism and crystallization phase state were investigated by the methods of atomic force microscopy (AFM) and X-ray diffraction (XRD). The pentacene films were deposited with a self-assembling monolayer by thermal evaporation on p(+)-Si wafer substrates at room temperature and annealed at a constant temperature (80 degrees C) for 120 min. The experimental results show that pentacene films were grown with terraces island structure with the diameter of island of about 100 nm and constituted a layer consisting of faceted grains with a average step height between terraces of 1.54 nm x s(-1), which were accord with the long axis length of pentacene molecule, and the film were vertically grown on the substrate surface. The crystallization of pentacene thin films is shown in XRD pattern. The increase in the thin film thickness introduced a second set of diffraction peaks, which were attributed to the pentacene triclinic bulk phase. The critical thickness of both phases is 150 and 80 nm, respectively. At a film thickness of 150 nm, the triclinic phase diffraction peaks become the dominant phase. This is contrast to the XRD spectrum of very thin film of 80 thickness, where the thin film phase is the only contribution.
