Effect of pre-aggregation in conjugated polymer solution on performance of diketopyrrolopyrrole-based organic field-effect transistors

Dereje, Mamo Melaku,Ji, Dongseob,Kang, So-Huei,Yang, Changduk,Noh, Yong-Young Applied Science Publishers 2017 Dyes and pigments Vol.145 No.-

<P><B>Abstract</B></P> <P>In this work, we investigate the effect of pre-aggregated solutions of diketopyrrolopyrrole (DPP)-based conjugated polymers to achieve highly-aligned polymer films for high-performance organic field-effect transistors (OFETs). A suitable marginal solvent is selected for 5-octyl-pentadecyl branched DPP and selenophene-based semiconducting polymer (PDPP(SE)-ε-C<SUB>8</SUB>C<SUB>15</SUB>) by utilizing the Hansen solubility parameter calculation. The anisotropic one-dimensional aligned PDPP(SE)-ε-C<SUB>8</SUB>C<SUB>15</SUB> film was off-center spin-coated from the pre-aggregated solution is studied by atomic force microscopy and polarized UV-Vis absorption spectroscopy. A significantly high hole mobility of 4.16 cm<SUP>2</SUP>V<SUP>−1</SUP>s<SUP>−1</SUP> was achieved from the OFETs with a unidirectionally-aligned PDPP(SE)-ε-C<SUB>8</SUB>C<SUB>15</SUB> film to the transistor channel direction.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Selection of suitable solvent for preparing pre-aggregated solutions of polymers. </LI> <LI> Formation of anisotropic thin films from the pre-aggregated polymer solutions. </LI> <LI> Directionally aligned polymer films differ in property and their FET performances. </LI> <LI> Thin films aligned parallel to the transistor channel direction show high mobility. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Self-aligned patterning of conductive films on plastic substrates for electrodes of flexible electronics

Mamo, Melaku Dereje,Shin, Eun-Sol,Noh, Yong-Young The Royal Society of Chemistry 2017 Journal of materials chemistry. C, Materials for o Vol.5 No.41

<▼1><P>We report a reliable and low-cost self-aligned patterning process for the formation of conducting polymer electrodes with a high resolution on flexible plastic substrates.</P></▼1><▼2><P>We report a reliable and low-cost self-aligned patterning process for the formation of conducting polymer electrodes with a high resolution on flexible plastic substrates. To realize high resolution and self-aligned patterning on the poly(ethylene 2,6-naphthalate) substrate, hydrophilic hydroxyl anchoring groups are formed by the photochemical oxidation reaction of an ammonium persulfate salt. Next, a hydrophobic octadecyltrichlorosilane (OTS) self-assembled monolayer is formed by immersing the substrate into an OTS solution. Selective UV/ozone irradiation with a wavelength of 171 nm through a shadow mask can define the OTS SAM as surface hydroxyl groups on the PEN surface by breaking the chemical bond between the OTS and the hydroxyl group. The selective irradiation process induces the formation of distinct hydrophilic (OH) and hydrophobic (OTS) surfaces with a resolution of 60 μm. As a conducting ink, poly(3,4-ethylenedioxythiophene)polystyrene sulfonate (PEDOT:PSS) is coated and self-aligned on the patterned arrays of the source/drain (S/D) electrodes of organic field-effect transistors (OFETs). Finally, using the recent widely used organic semiconductors such as poly(3-hexylthiophene), poly-[2,5-bis(2-octyldodecyl)-3,6-di(thiophen-2-yl)pyrrolo[3,4-<I>c</I>]pyrrole-1,4(2<I>H</I>,5<I>H</I>)-dionel-<I>alt</I>-thieno[3,2-<I>b</I>]thiophene], and poly{[<I>N</I>,<I>N</I>′bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-<I>alt</I>-5,5′-(2,2′-bithiophene)}, we demonstrate p-channel, n-channel, and ambipolar OFETs with a self-aligned PEDOT:PSS electrode of 50–100 μm channel length. All OFETs show a reasonably high and comparable field-effect mobility compared to identical devices with Au electrodes, and showed excellent mechanical stability in bending tests.</P></▼2>

Isoindigo benzodifurandione based conjugated polymers for high performance organic field-effect transistors

Takaya, Tomotsugu,Mamo, Melaku Dereje,Karakawa, Makoto,Noh, Yong-Young The Royal Society of Chemistry 2018 Journal of Materials Chemistry C Vol.6 No.29

<P>We report isoindigo based copolymers, poly(isoindigo benzodifurandione-bithiophene-alkoxyl) (PIBDF-BTO) and poly(isoindigo-bithiophene-alkoxyl) (PI-BTO) for high performance organic field-effect transistors (OFETs). PIBDF-BTO was synthesized by introducing strong electron withdrawing BDF into the acceptor isoindigo unit of PI-BTO to deepen the polymer highest occupied molecular orbital and the lowest unoccupied molecular orbital. This modification provided better polymer chain crystallinity and connectivity in thin film through increased intermolecular interactions and larger co-planarity in PIBDF-BTO. X-ray diffraction and atomic force microscopy showed higher crystallinity and well-arranged nano-fibril morphological PIBDF-BTO film compared with PI-BTO film. PIBDF-BTO OFETs showed much higher field effect mobility with well-balanced ambipolar transport with hole and electron mobilities of 0.27 and 0.22 cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP> compared to PI-BTO OFETs with hole mobility 0.004 cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP> and very low electron mobility. PIBDF-BTO also showed better hole and electron injection properties due to the narrower band gap (0.97 eV) compared to PI-BTO (1.35 eV). PI-BTO and PIBDF-BTO OFETs were operationally stable with negligible threshold voltage shift after continuous cycling measurements.</P>

Donor unit effect on DPP based organic field-effect transistor performance

Takaya, Tomotsugu,Mamo, Melaku Dereje,Karakawa, Makoto,Noh, Yong-Young Applied Science Publishers 2018 Dyes and pigments Vol.158 No.-

<P><B>Abstract</B></P> <P>We report diketopyrrolopyrrole (DPP) based copolymers, poly (diketopyrrolopyrrole-cyclopentadithiophene) (PDPPTT-CPDT) and poly(diketopyrrolopyrrolebenzo[1,2-b:4,5-b’]dithiophene) (PDPPTT-BDT) to investigate donor unit structure effects on organic field-effect transistor (OFET) performance. The highest occupied molecular orbital (HOMO) level and copolymer band gap were tuned by introducing different donor units on the acceptor DPP backbone. PDPPTT-BDT OFETs show 10 fold higher hole field-effect mobility, up to 0.08 cm<SUP>2</SUP> V<SUP>−1</SUP> s<SUP>−1</SUP>, than PDPPTT-CPDT OFETs due to better crystallinity and higher HOMO energetic levels. PDPPTT-CPDT and PDPPTT-BDT were operationally stable with negligible threshold voltage shift after cycling.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Two DPP based copolymers with different donor units are reported for OFET application. </LI> <LI> Introduction of different donor units tuned copolymer HOMO/LUMO levels and band gaps. </LI> <LI> Photophysical properties exhibited distinct thin film molecular interactions and crystallinities. </LI> <LI> PDPPTT-BDT exhibited stronger p-type properties with 10-fold higher hole mobility OFETs. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Acceptor Unit Effects for Ambipolar Organic Field-Effect Transistors Based on TIPS-Benzodithiophene Copolymers

Henry Opoku,Chinna Bathula,Melaku Dereje Mamo,Nabeen K Shrestha,이태권,노용영 한국고분자학회 2019 Macromolecular Research Vol.27 No.1

Two narrow band gap triisopropylsilyl substituted benzo[1,2-b:4,5-b] dithiophene (TIPS-BDT) derivatives, P1 (1.65 eV) and P2 (1.46 eV) are synthesized for ambipolar organic field-effect transistors and complementary inverters. Two electron acceptor units, heptadecanyl substituted thieno[3,4-c]pyrrole-4,6-dione (TPD) and ethylhexyl substituted diketopyrrolo[3,4-c]pyrrole (DPP) are incorporated to tune the structure and resulting properties of the donor-acceptor type copolymers. Structural modification based on the acceptor unit variation, resulted in comparable electrochemical, optical, microstructural, and charge transporting properties, as well as environmental and operational stability. TIPS-BDT copolymers with TPD acceptor units show comparatively superior performance, with field effect mobility ~10-3 cm2V-1s-1 for both holes and electrons and inverter gain ~18 with poly(methyl methacrylate) gate dielectric.