We report on the fabrication and characterization of hybrid polymer light emitting device (HPLEDs) with high
brightness and simplicity in design with improved robustness than the conventional polymer light-emitting diodes. We
demonstrate the incorporation of Au capped inorganic titanium oxide TiO2 nanocomposite in electroluminescent polymer
and fabricated HPLED. We achieved enhanced optical properties of the device and the increased performance of the
HPLED is attributed from the electronic charge transport properties of Au capped metal oxide particles in the
electroluminescence polymer. The interfacial contact area of electroluminescence polymer and cathode increased by the
incorporated nanoparticles in the organic polymer phase thereby improved luminescence properties.
PPV derivatives, polymers with vinylene units, have their tendency to exhibit degradation, after irradiation with white
light or operation of the device, resulting in the appearance of a shifted absorption and emission band in the short
wavelength regions of the spectra. In order to reduce oxidation of the vinylene group, the vinylene group was cyclized
using two 5-membered rings. In this paper, we report the synthesis and properties of new copolymers utilizing
poly(5,5,10,10-tetrakis(2-ethylhexyl)-5,10-dihydroindeno[2,1-a]indene-2,7-diyl) (PININE) and benzothiadiazole (BT).
PININE copolymers with BT and thiophene units exhibit high PCE for polymer solar cells (PSCs). Under white light
illumination (AM 1.5 G, 100 mW/cm2), the cell based on PININEDTBT/PCBM as the active layer has a short circuit
current density (Isc) of 5.93 mA/cm2, a fill factor (FF) of 43 %, and PCE of 1.88 %. These copolymers have not only
good processability due to indenoindene unit, in which four alkyl groups can be incorporated, but also the strong and
uniform absorbance in the whole visible region.
New light-emitting PCPP derivatives, poly(4,4-bis{4-[(2-ethylhexyl)oxy]phenyl}-4H-cyclopenta[def]phen- anthrene)
(BEHP-PCPP), with stabilized blue emission is reported. The OLED with the configuration of ITO/PEDOT:PSS/BEHPPCPP/
Ca/Al generates EL emission with maximum peak at 430 nm, low turn-on voltage (9V), and CIE coordinates (x
= 0.19, y = 0.15) for the blue color without any filtering. The maximum brightness of the OLEDs using BEHP-PCPP
was 1034 cd/m2 at 15 V. The maximum luminescence efficiency of the polymer LEDs with BEHP-PCPP was 0.21
cd/A at 617 mA/cm2.
New fluorin-containing electroluminescent polymers in vinylene units, poly(2-dimethyldodecylsilyl-p-phenylenedifluorovinylene)
(DMDS-PPDFV), have been synthesized by GILCH polymerization. This polymer has been used
as the electroluminescent layers in light-emitting diodes (LEDs) (ITO/PEDOT/polymer/Al). DMDS-PPDFV shows
PL around λmax = 455 nm (exciting wavelength, 365 nm) and green EL around λmax =489nm. Attachment of two the
fluoro groups were introduced to poly(2-dimethydodecylsilyl-1,4-phenylenevinylene) (DMDS-PPV) to give DMDSPPDFV
in an attempt to increase the electron affinity of the parent polymer.
Fluorescent conjugated polymers have attracted much attention due to their potential applications in flat panel displays.
There are few studies on the degradation of the PPV film in air when irradiated. The photodegradation reaction is a chain
scission process involving oxygen in air to yield terminal 4-vinylbenzoic acid groups. The photodegradation of
conducting polymer may seriously effect the performance of electroluminescence devices.
In order to reduce oxidation of the vinylene group, the vinylic group was cyclized using carbon-containing 5-membered
rings. In case of PININE, it is possible to introduce four alkyl groups in the sp3 carbons in the bicycle, which will
increase the solubility of the polymer. PININE was used as the electroluminescence layer for the light-emitting diode.
PININE shows turn-on voltage of 6.5 V, and EL with maximum peak at 477 nm, maximum brightness of 2187 cd/m2 at
12 V, and efficiency of 0.34 cd/A at 162 mA/cm2. The change in luminescence following irradiation with white light on
the PININE was not observed. When irradiated with white light, the films of MEH-PPV showed significantly decreased
peaks of UV and PL. As compared to this, the films of PININE showed stable spectra when irradiated over same period of time.
By introducing a solution-based titanium oxide (TiOx) layer between the polymer and Al electrode in polymer lightemitting
diodes, we have demonstrated that the devices exhibit an enhanced efficiency. The TiOx layer reduces the
barrier height between the polymer and Al cathode, thereby facilitating the electron injection in the devices and
enhancing the device performance by achieving a balance of charge injection and transport between the electrons and
holes. Moreover, we also believe that the TiOx layers prevent the diffusion of metal ions into the emitting polymers
during the Al deposition process, and reduce the degree of quenching centers in the active polymers.
One of the problems limiting the device efficiency of polymer light-emitting diodes is the imbalance of charge injection and transport between the electrons and holes. This problem is particularly serious for the case of aluminum (Al) electrode. By introducing solution-based titanium oxide (TiOx) layer between the polymer and Al electrode, we have demonstrated that the devices exhibit an enhanced efficiency. The TiOx layer reduces the barrier height between the polymer and Al cathode, thereby facilitating the electron injection in the devices and enhancing the device performance. Moreover, we also believe that the TiOx layers prevent the diffusion of metal ions into the emitting polymers during the Al deposition process, reducing the degree of quenching centers in the active polymers.
One of the serious problems in polymer light-emitting diodes (PLEDs) is the difficulty of electron injection in the current PLEDs device of anode/polymer/cathode geometry. This is particularly true for the case of aluminum (Al) electrode. The work function of Al is too high to match with the Lowest Unoccupied Molecular Orbit (LUMO) level of the luminescent polymers, thereby lowering the device efficiency. In this work, by introducing solution-based titanium oxide (TiOx) thin film as an electron injection layer between the polymer and Al electrode, we demonstrate that the devices exhibit an enhanced efficiency. The TiOx layer reduces the barrier height between the polymer and aluminum (Al) cathode, thereby facilitating the electron injection in the devices.
Conjugated polymers with a stabilized blue emission are of importance for the realization of full-color displays using polymer light-emitting diodes. We report a new class of blue-emitting polymers utilizing a new back-bone, poly(2,6-(4,4-bis(2-ethylhexyl)-4H-cyclopenta [def] phenanthrene)) (PCPP). This material emits a stabilized, efficient blueelectroluminescence(EL) without exhibiting any peak in the long wavelength region (green region) even after prolonged annealing for 18 hours at an elevated temperature of 150°C in air. This attributes to the chemical structure of this new polymer. The backbone of PCPP intrinsically inhibits the formation of the keto-defects mainly responsible for the degradation to green color in typical poly(fluorine) type materials, thereby stabilizing the blue EL emission in the devices.
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