A new DCM derivative 4-(dicyanomethylene)-2-t-butyl-6-(9-ethylphenothiazine-2-enyl)-4H-pyran (DCPTZ) has been
used as an orange-red fluorescent dye molecule in organic light-emitting diodes (OLEDs). EL devices with the structure
ITO/PEDOT-PSS/α-NPD/Alq3:DCPTZ/Alq3/LiF/Al were fabricated with various DCPTZ doping concentrations. The
maxima in the EL spectra of the devices varied from 580 to 620 nm depending on the doping concentration of the dye
molecule. An EL device with 0.5% dopant concentration was found to exhibit a maximum brightness of 81,500 cd/m2 at
13.3 V and a power efficiency of 4.1 lm/W with CIE coordinates (0.51, 0.47) at a luminance of 100 cd/m2. White lightemitting
devices with the structure ITO/PEDOT-PSS/a-NPD/a-NPD:DCPTZ/DPVBi/Alq3/ LiF/Al were also fabricated.
The thickness of the blue light-emitting 1,4-bis(2,2-diphenylvinyl)benzene (DPVBi) layer was varied to obtain white
light emission. White light emission from the device was observed when the thickness of the DPVBi layer was greater
than 10 nm. The maximum brightness and power efficiency of the device with a 20 nm DPVBi layer were found to be
30,300 cd/m2 and 2.0 lm/W respectively, with CIE coordinates (0.33, 0.36). In addition, the white EL device exhibits a
relatively high color rendering index (CRI) of about 83.
Thermal annealing has been widely used to improve device performances of organic solar cells with regioregular (RR)
poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl C61-butyric acid methyl ester (PCBM) bulk heterojunction blends.
Especially, short-circuit current density (Jsc) of the thermally-annealed device is significantly increased compared to
that of the non-annealed one. The Jsc is proportional to the product of the carrier mobility and the number of
photogenerated carriers which depends on the photocarrier generation efficiency and carrier recombination lifetime.
Therefore, the enhanced Jsc implies that the thermal annealing can increase either the mobility and/or lifetime of the
photogenerated carriers. In order to understand which parameter is more affected by thermal annealing, we compared
the temperature dependence of the Jsc and carrier mobility of P3HT:PCBM (1:1, weight%) blend solar cells. The carrier
mobility, measured from a time-of-flight photoconductivity (TOF-PC) measurement, increases from about 10-5 cm2/Vs
to the order of 10-4 cm2/Vs as the temperature increases from 300 K to 360 K and then saturates above 360 K up to 400 K. This behavior is very similar to the temperature dependence of the current density of the P3HT:PCBM solar cell
devices with the same blend ratio. Therefore, this correlation indicates that the thermal annealing increases the carrier
mobility by improving morphological order of the blend film and thereby enhances the Jsc of the P3HT:PCBM blend
We report the fabrication and the characterization of white organic light-emitting diodes that exhibit high efficiency and very stable color coordinates over the wide range of bias voltages. The blue-emitting layer of 1,4-bis(2,2-diphenyl vinyl)benzene (DPVBi) is sandwiched between the red-emitting layers in which red fluorescent dyes of 4-dicyanomethylene-2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[i,j]quinolizin-8-yl)vinyl]-4H-pyran) (DCM2) are doped into the hole-transporting layer of 4,4’bis[N-(1-napthyl)-N-phenyl-amino]-biphenyl (α-NPD) and the electron-transporting layer of tris(8-hydroxyquinoline) aluminum (Alq3). The device structure is ITO/PEDOT:PSS/α-NPD(50 nm)/α-NPD:DCM2 (5 nm, 0.2 %)/DPVBi(10 nm)/Alq3:DCM2(5 nm, 0.2 %)/Alq3(40 nm)/LiF(0.5 nm)/Al. The partial energy transfer from the blue layer to the nearby red layers results in white light emission with the stable color coordinates of (0.36, 0.37). The device shows the luminous efficiency of about 3.6 lm/W at 100 cd/m2 and the maximum luminance of 40,650 cd/m2 at the bias of 12 V.