New electroluminescent copolymers with fluoro groups in vinylene unit, poly(9,9-di-hexylfluorene-2,
7-vinylene-co-pphenylenedifluorovinylene)
(PFVPDFV), have been synthesized by the GILCH polymerization. The fluoro groups were
introduced on vinylene units to increase the electron affinities of the copolymers. The PFVPDFVs exhibit absorption
spectra with maximum peaks at 371 ~ 413 nm. In the PL spectra of PFVPDFVs, as the PDFV content increases up to
50% in the copolymer system, fwhm was decreased by 4 - 38 nm as compared to PFV. The HOMO energy levels of the
copolymers were about 5.25 - 5.50 eV, and the LUMO energy levels were about 2.67-2.97 eV. The polymer LEDs
(ITO/PEDOT/polymer/Al) of PFVPDFVs showed emission with maximum peaks at around 472 - 538 nm. By adjusting
the feed ratios of PDFV in the copolymers, it was possible to tune the emission colors from greenish yellow to orange
depending on the obtained CIE coordinates. The luminescence efficiencies of the copolymers at room temperature are
about 0.1-1.47 cd/A. The introduction of up to 50 % of PDFV in PFVPDFVS can enhance the device performance to
result in high current density, brightness and efficiency due to the increased electron injection ability caused by the
presence of fluoro groups in the vinylene units.
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 electroluminescent polymer with tetrakis-alkoxy group, poly[2,3,5,6-tetrakis(2-ethylhexyloxy)-1,4-
phenylenevinylene] (TEH-PPV), has been synthesized by the Gilch polymerization. TEH-PPV with tetrakisethylhexyloxy
groups in phenylene unit can get shorter conjugation length than MEH-PPV, and had more blue shifted
absorption and emission peaks due to steric hindrance. Tetrakis-ethylhexyloxy groups induced very conjugated
backbone is twisted. And, they can enhance the internal efficiency of the conjugated polymer as emissive layer in
PLED because of the restraint of inter-chain interaction by the avoidance of close packing to give decent device
performance.
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.
A novel blue emitters, 2-[10-(4,4-dioctyl-4H-cyclopenta[def]phenanthrene-2-yl)-9-anthryl]-4,4-dioctyl-4Hcyclopenta[
def]phenanthrene (OCPA) and 4,4,4',4',4",4"-hexaoctyl-2,6':2',6"-ter cyclopenta[def]-phenanthrene
(TerCPP), has been synthesized and characterized. The introduction of CPP units into the structure of OCPA and
TerCPP leads to high efficiency and pure blue color property. Thermal analysis of OCPA and TerCPP reveals their high
thermal stability. Their decomposition temperatures, which correspond to a 5% weight loss upon heating during TGA,
are around 410 °C for OCPA and 425 °C for TerCPP. The high-quality amorphous films of OCPA and TerCPP with good
morphological stability can be prepared by vapor deposition. Multilayer organic EL devices constructed using OCPA
and TerCPP as an emitting layer produced bright blue emissions. The UV-visible absorption spectra of theses
compounds appear at about 290-400 nm, and their maximum PL emission spectra of OCPA and TerCPP in THF solution
appeared at about 438 nm and 390 nm, respectively. The EL spectra showed maximum peaks at about 434 nm and 440
nm, respectively. The turn-on voltage of compounds was about 6V, and the luminous efficiency is 1.0-1.2 cd/A.
Emission color of OCPA was deep blue and CIE coordinate (0.16, 0.11) is quite close to that of the National Television
System committee (NTSC) standard vlue (0.14, 0.88).
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.
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.
We fabricated polymer-fullerene photovoltaic (PV) devices using various conjugated polymers, poly[2-methoxy-5-(2’-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), poly{2-[4-(3,7-dimethyloctyloxy)-phenoxy]-1,4-phenylenevinyl-ene} (p-DMOP-PPV), and their copolymer system, p-DMOP-co-MEH-PPV. By comparing PV characteristics of such devices with a systematic change of the energy levels (ionization potential Ip and electron affinity Ea), we investigated the origin of open circuit voltage (Voc) of the devices. Our results indicate that the magnitude of Voc is governed by the difference between Ea of the fullerene and Ip of the polymer, which is not consistent with previous consideration of the work function difference between electrodes as in conventional metal-insulator-metal type devices.
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