Heat treatment-induced enhancement in the optical spectra of poly(3,4-ethylenedioxythiophene)/poly(stylenesulfonate) films

Shinuk Cho,이광희 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.46 No.4

We present optical reflectance, R(!), measurements on free-standing films of poly(3,4-ethylenedioxythiophene)/poly(stylenesulfonate) (PEDOT/PSS) with a dc conductivity of 100 S/cm prepared at an elevated temperature of 60 C. The optical conductivity, (!), obtained from a Kramers-Kronig analysis of R(!) exhibits an enhanced response in the intraband transitions below 1.0 eV as compared with those of the films prepared at room temperature. Based on the morphology and microstructure analysis, we attribute this to a polymeric structure improvement in the heat-treated samples. The heat-annealing effect increases the degree of crystallinity of the films, resulting in enhanced physical properties of the PEDOT/PSS system.

Effects of processing additive on bipolar field-effect transistors based on blends of poly(3-hexylthiophene) and fullerene bearing long alkyl tails

Cho, Shinuk,Nho, Sung-Ho,Eo, Maengsun,Lee, Min Hyung Elsevier 2014 ORGANIC ELECTRONICS Vol.15 No.5

Bipolar FETs (BiFETs) based on the bulk heterojunction system comprised of various ratios of P3HT and soluble fullerene derivatives are demonstrated. We studied the effect of addition of small concentrations of the processing additive, 1,8-octanedithiol (ODT), on gate-induced transport properties. The control blend system consisting of poly (3-hexylthiophene) (P3HT) and phenyl-C61-butyric acid methyl ester (PCBM) showed enhanced hole transport properties with the addition of the ODT additive. However, electron transport properties were diminished in the presence of ODT additive because of the relatively isolated PCBM phase between the large-scale segregation of the P3HT amorphous phase. The BHJ BiFET based on P3HT and soluble fullerene derivatives bearing long alkyl tails (FP-Ph-OC10) showed enhanced performance in both hole and electron transport when the ODT additive was applied. We attribute the enhancement of hole mobility to well-formed P3HT fibrilla structures of P3HT caused by the alkyl-alkyl interaction assisted by both the ODT additive and alkyl side chain in FP-Ph-OC10. As the P3HT forms fibrilla structures, connection to the isolated FP-Ph-OC10 phase be formed, resulting in a continuous electron pathway, thereby improving electron mobility. This suggests that not only the selective solubility, but also the alkyl-alkyl interaction between the side-chain and ODT additive may affect the phase segregation of BHJ mixtures. (C) 2014 Elsevier B.V. All rights reserved.

Interface Engineering for High Efficient Non-fullerene Polymer Solar Cells

Shinuk Cho(조신욱),박수정,Febrian Tri Adhi Wibowo,오승환,장성연 한국고분자학회 2021 한국고분자학회 학술대회 연구논문 초록집 Vol.46 No.1

In current, the low-conductivity PEDOT:PSS is mainly utilized in contemporary solar cells. Thus, the contact between ITO and PEDOT:PSS is not ohmic anymore. Despite the high possibility that there are serious interface problems, little attention has been paid to the interface between PEDOT:PSS and ITO. In this work, we have employed a conjugated polyelectrolyte (WPFSCz-) between ITO and low-σ PEDOT:PSS to overcome organic-inorganic interfacial problems. Insertion of the WPFSCz- layer provides substantial advantages in the operation of the polymer solar cells. First, WPFSCz- layer modifies the work-function of the ITO, thereby forming effective cascading energy alignment. Second, the WPFSCz- layer eliminates interfacial trap sites, resulting in an improvement of fill factor. These effects result in a significant increase in the efficiency of non-fullerene solar cells based on PM6 and Y6, from 15.86 to 17.34%.

Poly(diketopyrrolopyrrole‐benzothiadiazole) with Ambipolarity Approaching 100% Equivalency

Cho, Shinuk,Lee, Junghoon,Tong, Minghong,Seo, Jung Hwa,Yang, Changduk WILEY‐VCH Verlag 2011 Advanced Functional Materials Vol.21 No.10

<P><B>Abstract</B></P><P>As a characteristic feature of conventional conjugated polymers, it has been generally agreed that conjugated polymers exhibit either high hole transport property (p‐type) or high electron transport property (n‐type). Although ambipolar properties have been demonstrated from specially designed conjugated polymers, only a few examples have exhibited ambipolar transport properties under limited conditions. Furthermore, there is, as yet, no example with ‘equivalent’ hole and electron transport properties. We describe the realization of an equivalent ambipolar organic field‐effect transistor (FET) by using a single‐component visible–near infrared absorbing diketopyrrolopyrrole (DPP)‐benzothiadiazole (BTZ) copolymer, namely poly[3,6‐dithiene‐2‐yl‐2,5‐di(2‐decyltetradecyl)‐pyrrolo[3,4‐<I>c</I>]pyrrole‐1,4‐dione‐5’,5’’‐diyl‐<I>alt</I>‐benzo‐2,1, 3‐thiadiazol‐4,7‐diyl] (<B>PDTDPP‐<I>alt</I>‐BTZ</B>). <B>PDTDPP‐<I>alt</I>‐BTZ</B> shows not only ideally balanced charge carrier mobilities for both electrons (<I>▴<SUB>e</SUB></I> = 0.09 cm<SUP>2</SUP>V<SUP>−1</SUP>s<SUP>−1</SUP>) and holes (<I>▴<SUB>h</SUB></I> = 0.1 cm<SUP>2</SUP>V<SUP>−1</SUP>s<SUP>−1</SUP>) but also its inverter constructed with the combination of two identical ambipolar FETs exhibits a gain of ∼35 that is much higher than usually obtained values for unipolar logic.</P>

Enhanced Performance of Fullerene n-Channel Field-Effect Transistors with Titanium Sub-Oxide Injection Layer

Cho, Shinuk,Seo, Jung Hwa,Lee, Kwanghee,Heeger, Alan J. WILEY-VCH Verlag 2009 Advanced Functional Materials Vol.19 No.9

<P>Enhanced performance of n-channel organic field-effect transistors (OFETs) is demonstrated by introducing a titanium sub-oxide (TiO<SUB>x</SUB>) injection layer. The n-channel OFETs utilize [6,6]-phenyl-C<SUB>61</SUB> butyric acid methyl ester (PC<SUB>61</SUB>BM) or [6,6]-phenyl-C<SUB>71</SUB> butyric acid methyl ester (PC<SUB>71</SUB>BM) as the semiconductor in the channel. With the TiO<SUB>x</SUB> injection layer, the electron mobilities of PC<SUB>61</SUB>BM and PC<SUB>71</SUB>BM FET using Al as source/drain electrodes are comparable to those obtained from OFETs using Ca as the source/drain electrodes. Direct measurement of contact resistance (R<SUB>c</SUB>) shows significantly decreased R<SUB>c</SUB> values for FETs with the TiO<SUB>x</SUB> layer. Ultraviolet photoelectron spectroscopy (UPS) studies demonstrate that the TiO<SUB>x</SUB> layer reduces the electron injection barrier because of the relatively strong interfacial dipole of TiO<SUB>x</SUB>. In addition to functioning as an electron injection layer that eliminates the contact resistance, the TiO<SUB>x</SUB> layer acts as a passivation layer that prevents penetration of O<SUB>2</SUB> and H<SUB>2</SUB>O; devices with the TiO<SUB>x</SUB> injection layer exhibit a significant improvement in lifetime when exposed to air.</P> <B>Graphic Abstract</B> <P>Enhanced performance of fullerene organic field-effect transistors (OFETs) is demonstrated by introducing a TiO<SUB>x</SUB> injection layer that essentially eliminates the contact resistance between the electrodes and the active layer. The TiO<SUB>x</SUB> layer also serves to protect the device against penetration of O<SUB>2</SUB> and H<SUB>2</SUB>O, and thereby leads to a significant improvement in the lifetime of OFETs when exposed to air. <img src='wiley_img/1616301X-2009-19-9-ADFM200900189-content.gif' alt='wiley_img/1616301X-2009-19-9-ADFM200900189-content'> </P>

Extended Lifetime of Organic Field-Effect Transistors Encapsulated with Titanium Sub-Oxide as an ‘Active’ Passivation/Barrier Layer

Cho, Shinuk,Lee, Kwanghee,Heeger, Alan J. WILEY-VCH Verlag 2009 Advanced Materials Vol.21 No.19

<B>Graphic Abstract</B> <P>A thin capping layer of titanium sub-oxide (TiOx) prepared by sol–gel synthesis from titanium alkoxides extends the lifetime of organic FETs. The TiO<SUB>x</SUB> layer functions as an ‘active’ passivation/barrier layer that actually removes oxygen and water vapor from the organic semiconductor. The results demonstrate a significant improvement in the lifetime of organic field-effect transistors when exposed to air. <img src='wiley_img/09359648-2009-21-19-ADMA200803013-content.gif' alt='wiley_img/09359648-2009-21-19-ADMA200803013-content'> </P>

Reflectance Study on the Metal-Insulator Transition Driven by Crystallinity Change in Poly(3,4-ethylenedioxythiophene)/Poly(stylenesulfonate) Films

Shinuk Cho,이광희,Sung Heum Park 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.47 No.2

We report optical reflectance, R(!), studies on free-standing films of poly(3,4-ethylenedioxythiophene)/poly(stylenesulfonate) (PEDOT-PSS) measured over a range from 0.02 . 5.0 eV. When the PEDOT-PSS films were prepared at an elevated temperature of 60 C, the films exhibit an increased dc-conductivity (dc 104 S/cm) and an optical conductivity, (!), in the intraband transitions below 1.0 eV as compared with the films prepared at room temperature (dc 47 S/cm). Detailed analysis of (!) in terms of the “localization-modified Drude (LMD) model” demonstrated that the heat-treated PEDOT-PSS was a disordered metal near the metal-insulator transition (MIT) while the as-grown films could be better described as a Fermi glass on the insulating side of MIT. The heat-annealing process increased the degree of crystallinity of the films, thereby inducing a MIT near the critical limit.

Optical Spectra of Indium-Tin-Oxide Films Deposited on Flexible Colorless Polyimide Substrates

Shinuk Cho,Kwanghee Lee,Chang-Sik Ha,Hyuntaek Lim 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.48 No.3

We report optical spectra measurements on indium tin oxide (ITO) films deposited on colorless fluorine-containing aromatic polyimide substrates. As the deposition temperature (TD) of the substrates increases from room temperature to 200 C, the transmittance and the reflectance spectra exhibit more metallic features. However, the detailed dependence of the optical parameters on TD is not consistent with the dc-conductivity (dc). We attribute this to a reduced mean free time ( ) of charge carriers for the high TD samples. For TD > 100 C, tin atoms migrate from grain boundaries to regular lattice sites, acting as impurities and thereby decreasing . As a consequence, in spite of the increasing charge carrier density with TD as revealed by the optical measurements, the reduced limits dc for the high TD samples.0

A Thermally Stable Semiconducting Polymer

Cho, Shinuk,Seo, Jung Hwa,Park, Sung Heum,Beaupré,, Serge,Leclerc, Mario,Heeger, Alan J. WILEY-VCH Verlag 2010 Advanced Materials Vol.22 No.11

<B>Graphic Abstract</B> <P>The thermal stability of the poly(2,7-carbazole) derivative (PCDTBT) is investigated. UV–visible absorption spectra and X-ray photoelectron spectroscopy data demonstrate that the electronic structure of PCDTBT is stable in air at annealing temperatures up to 150 °C and in N<SUB>2</SUB> even after exposure to temperatures up to 350 °C. Field-effect transistors fabricated with PCDTBT show stable characteristics and hole mobility up to 150 °C (air) and 350 °C (N<SUB>2</SUB>). <img src='wiley_img_2010/09359648-2010-22-11-ADMA200903420-content.gif' alt='wiley_img_2010/09359648-2010-22-11-ADMA200903420-content'> </P>

Energy Loss Analysis for Non-Fullerene Organic Solar Cells

조신욱(Shinuk Cho) 한국고분자학회 2022 한국고분자학회 학술대회 연구논문 초록집 Vol.47 No.1