Soon Ki Kwon

Synthesis and Characterization of Organic Light-Emitting Copolymers Containing Naphthalene

Conjugated PPV-derived block copolymers containing 2-ethylhexyloxynaphthalene unit were synthesized and characterized in this study. The resulting polymers were soluble in common organic solvents and showed good thermal stabilities. The weight-average molecular weights (Mw) of the copolymers ranged from 246,000 to 475,000 with PDIs of 1.3∼2.1. The optical properties of these polymers, measured both in a chloroform solution and on a film, showed a maximum absorption at 405∼476 nm for Copolymers I∼VIII. In the PL spectra, Copolymers I∼VIII showed maximum peaks at 510∼566 nm. The HOMOs, LUMOs and band gaps of the PPV derivatives of Copolymers I∼VIII were 5.30∼5.77, 3.04∼3.24, and 2.5∼2.2 eV, respectively. The multi-layered, light-emitting diodes of ITO/PEDOT/copolymers/LiF/Al exhibited turn-on voltages of 6∼2.5 V. Copolymer VIII exhibited the maximum brightness of 3,657 cd/m2. Particularly, Copolymer VII, with an identical composition of MEH-PPV and naphthalene-PPV, showed a maximum luminance efficiency and power efficiency of 2.63 cd/A and 1.06 lm/W, respectively.

Highly Stable Polymer Solar Cells Based on Poly(dithienobenzodithiophene-co-thienothiophene)

It is important to develop new donor (D)− acceptor (A) type low band gap polymers for highly stable polymer solar cells (PSCs). Here, we describe the synthesis and photovoltaic properties of two D−A type low band gap polymers. The polymers consist of dithienobenzodithiophene (DTBDT) moieties with expanded conjugation side groups as donors and 2-ethyl-1-(thieno[3,4-b]thiophen-2-yl)hexan-1-one (TTEH) or 6-octyl-5H-thieno[3′,4′:4,5]thieno[2,3-c]pyrrole5,7(6H)-dione (DTPD) as acceptors to give pDTBDT-TTEH and pDTBDT-DTPD polymers, respectively. The pDTBDTTTEH is quite flat, resulting in a highly crystalline film. In contrast, the pDTBDT-DTPD is highly twisted to yield an amorphous film. Photovoltaic devices based on pDTBDT-TTEH and pDTBDT-DTPD exhibited power conversion efficiencies (PCEs) of 6.74% and 4.44%, respectively. The PCE difference results mainly from morphological differences between the two polymer:PC71BM blend films; the pDTBDT-TTEH polymer formed a nanoscopically networked domains in the blend state, while the pDTBDT-DTPD polymer film contained aggregated domains with large phase separation between the polymer and PC71BM molecules. Importantly, we observed that pDTBDT-TTEH-based devices showed excellent stabilityin air, retaining 95% of the initial PCE after storage for over 1000 h without encapsulation. The high stability of the pDTBDT-TTEH-based device was originated mainly by the crystalline nature of the pDTBDT-TTEH:PC71BM film. This work suggests that designing highly conjugated planar backboned polymers is crucial to improve not only the photovoltaic performance but also the stability of PSCs.

Synthesis and characterization of new blue light emitting alternating terphenylenevinylene carbazylenevinylene copolymer

A new terphenylenevinylene carbazylenevinylene alternating copolymer with the advantage of poly(p-phenylenevinylene) (PPV), poly(p-phenylene)(PPP) and poly(carbazole) was designed, synthesized and characterized. The polymer structure was confirmed by various spectroscopic analyses and the number average molecular weight (Mn) of the obtained polymer was 7,800. The resulting polymer was thermally stable with high glass transition temperature (Tg) (150°C), and was readily soluble in common organic solvents. Cyclic voltammetry study revealed that the HOMO and LUMO energy levels of the polymer were 5.37 and 2.47 eV, respectively. The ITO/ PEDOT/polymer/Al device fabricated from the polymer emitted bright sky blue light with a maximum peak of around 478 nm. The device showed the maximum brightness of 1,200 nW with a turn-on voltage of 7 V.

Design and synthesis of new fluorene-based blue light emitting polymer containing electron donating alkoxy groups and electron withdrawing oxadiazole

A new polyfluorene-based copolymer having 2-ethylhexyloxy-5-methoxy-1,4-phenylene as an electron donating group and 2,5-diphenyl-oxadiazole as an electron withdrawing group was synthesized by the Suzuki coupling reaction. The obtained copolymer was characterized by1H-NMR,13C-NMR, and IR-spectroscopy. The weight average molecular weight (Mw) of the obtained polymer was 18,600 with a polydispersity index of 1.5. The maximum photoluminescence of the solution and film of the polymer was observed at 453 nm and 456 nm, respectively. A double-layer device with the configuration, ITO/PEDOT/copolymer/Al, emitted blue light at 460 nm.

Synthesis and Characterization of Poly(fluorenylenevinylene-terphenylenevinylene) Containing Phenyl Pendant Group

Poly(fluorenylenevinylene-terphenylenevinylene) containing phenyl pendant group was synthesized by Suzuki coupling reaction and characterized by1H-NMR,13C-NMR, and IR-spectrum. The weight average molecular weight (Mw) of the obtained polymer was 31,000 with a polydispersity index of 1.9. The polymer showed good solubility in common organic solvents, and the solution and film emitted blue emission (λmax=460 nm) on irradiation with UV light. The ITO/PEDOT/polymer/Al device fabricated using the polymer as an emitting layer emitted blue light with a maximum peak around 460 nm. The maximum efficiency of the device was 0.011%.

Synthesis and characterization of a new PPV derivative containing a sterically hindered 2,5-dimethylphenyl group

A new poly[2-(2′,5′-dimethylphenyl)-1,4-phenylenevinylene] (PDMPPV) that features a bulky 2′,5−dimethylphenyl substituent, which can induce steric hindrance between the PPV backbone and the methyl groups, was designed and synthesized. The polymer structure having no TBB defects was confirmed by1H-NMR and13CNMR spectroscopy. The polymer showed good thermal stability with highTg. The polymer film showed a maximum absorption at 415 nm with an absorption onset at 480 nm. The maximum emission peak showed at ca. 515 nm, with a shoulder at 530 nm. The turn-on voltages of ITO/PEDOT/PDMPPV/Al and ITO/PDMPPV/Al devices were 8 and 10 V, respectively. The electroluminescence spectrum from the device showed a maximum peak at 510 nm with a shoulder at ca. 535 nm.

The Alignment of Liquid Crystals on the Film Surfaces of Soluble Aromatic Polyimides Bearing t-Butylphenyl and Trimethylsilylphenyl Side Groups

With the study goal of firstly elucidating the anisotropic interactions between oriented polymer chain segments and liquid crystal (LC) molecules, and secondly of determining the contributions of the chemical components of the polymer segments to the film surface topography, LC alignment, pretilt, and anchoring energy, we synthesized three dianhydrides, 1,4-bis(4′-t-butylphenyl)pyromellitic dianhydride (BBPD), 1,4-bis(4′-trimethylsilylphenyl)pyromellitic dianhydride (BTPD), and 2,2′-bis(4″-tert-butylphenyl)-4,4′,5,5′-biphenyltetracarboxylic dianhydride (BBBPAn), and a series of their organosoluble polyimides, BBPD-ODA, BBPD-MDA, BBPD-FDA, BTPD-FDA, and BBBPAn-FDA, which contain the diamines 4,4′-oxydianiline (ODA), 4,4′-methylenediamine (MDA), and 4,4′-(hexafluoroisopropylidene) dianiline (FDA). All the polyimides were determined to be positive birefringent polymers, regardless of the chemical components. Although all the rubbed polyimide films exhibited microgrooves which were created by rubbing process, the film surface topography varied depending on the polyimides. In all the rubbed films, the polymer chains were unidirectionally oriented along the rubbing direction. However, the degree of in-plane birefringence in the rubbed film varied depending on the polyimides. The rubbing-aligned polymer chains in the polyimide films effectively induced the alignment of nematic LCs along their orientation directors by anisotropic interactions between the preferentially oriented polymer chain segments and the LCs. The azimuthal and polar anchoring energies of the LCs ranged from 0.45×10−4 – 1.37×10−4 J/m2 and from 0.86×10−5 – 4.26×10−5 J/m2, respectively, depending on the polyimides. The pretilt angles of the LCs were in the range 0.10–0.62°. In summary, the soluble aromatic polyimides reported here are promising LC alignment layer candidates for the production of advanced LC display devices.

The electrical and photoconductivity characteristics of donor-acceptor alternating copolymer using solution process

The authors report on the electrical and photoconductivity characteristics of donor-acceptor alternating copolymer, poly(dioctyloxinapthalenediketopyrrolopyrrole) (PONDPP) with Al/PONDPP/p-Si/Al hybrid organic/inorganic Schottky diode for optoelectronic applications. The fabricated device shows ideality factor value of 2.6 and barrier height of 0.68 eV obtained from current-voltage characteristics. The high rectification ratio of 1.86 × 104 and photo-responsivity of 55 mA/W at 650 nm is achieved. From results, we found that the fine photo-response and electrical characteristics are attributed to the modified band-gap structure to have Schottky barrier at highest occupied molecular orbital to valence band of silicon and high hole mobility of PONDPP.

Synthesis and Characteristics of New Poly(p-phenylenevinylene) with Bulky t-Octylphenoxy Group

A new 2,5-di(t-octylphenoxy) group substituted poly(p-phenylenevinylene) derivative was synthesized by Gilch polymerization. The obtained polymer was characterized by NMR, FT-IR, and chemical analysis and completely soluble in common organic solvents. The polymer showed good thermal stability withTgof 105 °C. The polymer dissolved in chloroform showed maximum emission at 514 nm with a shoulder peak at around 560 nm. The EL spectrum of the ITO/PEDOT/TOP-PPV/Al device was observed maximum emission at 545 nm with a shoulder peak at around 585 nm.

79.3: Effect of Surface Treatment on the Performance of TIPS Pentacene TFT by Inkjet Printing

We have studied the effect of self-assembled monolayer (SAM) on the performance of printed TFT for a bottom contact, bottom gate TFT. A 6,13-bis(triisopropylsilylethynyl) pentacene (TIPS pentacene) was inkjet printed on the Ag source and drain electrodes. To reduce the energy barrier (1.6 eV) between the pristine Ag and TIPS pentacene, the Ag layer was treated by pentafluorothiophenol. And we controlled the physical interactions at the semiconductor/gate dielectric(photoacryl) interface by inserting a hydrophobic SAM of organoalkyl-Silanes with octyltrichlorosilane or β-phenethyltrichlorosilane. The results show that the TIPS pentacene TFT with PFBT/PTS treatment has field-effect mobility of 0.18 cm2/Vs, subthreshold slope of 0.6 V/decade, and on/off current ratio of 107.