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Lee, Jiyoul,Chung, Jong Won,Jang, Jaeman,Kim, Do Hwan,Park, Jeong-Il,Lee, Eunkyung,Lee, Bang-Lin,Kim, Joo-Young,Jung, Ji Young,Park, Joon Seok,Koo, Bonwon,Jin, Yong Wan,Kim, Dae Hwan American Chemical Society 2013 Chemistry of materials Vol.25 No.9
<P>The influence of alkyl side chains on the crystallinity of semiconducting copolymer films and their sub-bandgap density-of-states (DOS), the latter being closely related to the stability and the device performance of organic field-effect transistors (OFETs), is investigated. Three different poly(hexathiophene-alt-bithiazole) (PHTBTz) based polymer semiconductors, with identical backbones but different side chain positions and lengths, were synthesized. The crystallinity examined by grazing incidence X-ray diffraction (GIXRD) strongly depends on the number, position, and length of each type of alkyl side chain attached to the thiophene and thiazole copolymer backbones. Also, the sub-bandgap trap DOS distributions were extracted by performing multiple-frequency capacitance–voltage (MF-CV) spectroscopy on the field effect devices. The relationship between film crystallinity and trap DOS in the field-effect transistors can be interpreted in terms of the complex interplay between the number, position, and length of each alkyl side chain for efficient π–π stacking. In particular, the number and position of the alkyl side chain attached to the polymer backbone significantly affects the device performance. Poly(tetryloctylhexathiophene-alt-dioctylbithiazole) (PHTBTz-C8) exhibits the best electrical performance among the different semiconductors synthesized, with a relatively low bulk trap density of ∼2.0 × 10<SUP>20</SUP> cm<SUP>–3</SUP> eV<SUP>–1</SUP> as well as reasonable hole mobility of ∼0.25 cm<SUP>2</SUP> V<SUP>–1</SUP> s<SUP>–1</SUP>. The microstructural analyses of this organic material strongly suggest that the short π–π stacking distance induces strong interaction between adjacent polymer backbones, which in turn results in enhanced electrical properties.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/cmatex/2013/cmatex.2013.25.issue-9/cm400592b/production/images/medium/cm-2013-00592b_0009.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/cm400592b'>ACS Electronic Supporting Info</A></P>
Lee, Kwang-Hee,Lee, Gae Hwang,Leem, Dong-Seok,Lee, Jiyoul,Chung, Jong Won,Bulliard, Xavier,Choi, Hyeonho,Park, Kyung-Bae,Kim, Kyu-Sik,Jin, Yong Wan,Lee, Sangyoon,Park, Soo Young American Chemical Society 2014 The Journal of Physical Chemistry Part C Vol.118 No.25
<P>The dynamic characterization of two green-sensitive organic photodetectors (OPDs) using nonfullerene small molecules is investigated by analyzing the electrical parameters based on the experimental results and the simulated data. The two OPDs comprise <I>N</I>,<I>N</I>-dimethyl quinacridone (DMQA) as the common donor and dibutyl-substituted dicyanovinyl terthiophene (DCV3T) or boron-subphthalocyanine chloride (SubPc) as respective acceptors. At the applied voltage of −5 V, the device composed of DMQA/SubPc shows a higher frequency response at 148.3 kHz, by 55 kHz higher than the device based on DMQA/DCV3T. The impedance spectroscopy results indicate that the former device exhibits the low resistance due to the high mobility and the low capacitance linked to the dielectric constant. According to the molecular quantum calculation, the linear structure of DCV3T may promote packing of adjacent molecules in the linear direction, resulting in a high polarizability. In contrast, the fused structure of SubPc leads to a decrease in reorganization energy, and its conical shape tends to counterbalance the net dipole at the axial position in the dimer packing configuration owing to the symmetry of the three-branched units in the molecular periphery, which are related to the high carrier mobility and the low dielectric constant. The OPD comprising SubPc, with the dynamic response surpassing the commercialization level of 100 kHz, also exhibits good static performance with an external quantum efficiency of 60.1% at the wavelength of 540 nm, which can be an interesting candidate for potential applications as image sensors.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2014/jpccck.2014.118.issue-25/jp5028788/production/images/medium/jp-2014-028788_0008.gif'></P>
Lee, Jiyoul,Chung, Jong Won,Kim, Do Hwan,Lee, Bang-Lin,Park, Jeong-Il,Lee, Sangyoon,Hä,usermann, Roger,Batlogg, Bertram,Lee, Sang-Soo,Choi, Insil,Kim, Il Won,Kang, Moon Sung American Chemical Society 2015 JOURNAL OF THE AMERICAN CHEMICAL SOCIETY - Vol.137 No.25
<P>We report the observation of band-like transport from printed polymer thin films at room temperature. This was achieved from donor-acceptor type thiophene-thiazole copolymer that was carefully designed to enhance the planarity of the backbone and the resulting transfer integral between the macromolecules. Due to the strong molecular interaction, the printed polymer film exhibited extremely low trap density comparable to that of molecular single crystals. Moreover, the energy barrier height for charge transport could be readily reduced with the aid of electric field, which led formation of extended electron states for band-like charge transport at room temperature.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jacsat/2015/jacsat.2015.137.issue-25/jacs.5b04253/production/images/medium/ja-2015-04253w_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/ja5b04253'>ACS Electronic Supporting Info</A></P>
Lee, Jiyoul,Chung, Jong Won,Yoon, Gyu Bok,Lee, Moo Hyung,Kim, Do Hwan,Park, Jozeph,Lee, Jin-Kyun,Kang, Moon Sung American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.44
<P>Field-effect mobility of a polymer semiconductor film is known to be enhanced when the gate dielectric interfacing with the film is weakly polarizable. Accordingly, gate dielectrics with lower dielectric constant (k) are preferred for attaining polymer field-effect transistors (PFETs) with larger mobilities. At the same time, it is also known that inducing more charge carriers into the polymer semiconductor films helps in enhancing their field-effect mobility, because the large number of traps presented in such a disorder system can be compensated substantially: In this sense, it may seem that employing higher k dielectrics is rather beneficial because capacitance is proportional to the dielectric constant. This, however, contradicts with the statement above. In this study, we compare the impact of the two, i.e., the polarizability and the capacitance of the gate dielectric, on the transport properties of poly[(diketopyrrolopyrrole)-alt-(2,2'-(1,4-phenylene)bisthiophene)] (PDPPTPT) semiconductor layers in an FET architecture. For the study, three different dielectric layers were employed: fluorinated organic CYTOP (k = similar to 2) poly(methyl methacrylate) (k = similar to 4) and relaxor ferroelectric poly(vinylidene fluoride-trifluoroethylene-chlorotrifluoroethykne) (k = similar to 60). The beneficial influence of attaining more carriers in the PDPPTPT films on their charge transport properties was consistently observed from all three systems. However, the more dominant factor determining the large carrier mobility was the low polarizability of the gate dielectric rather than its large capacitance; field-effect mobilities of PDPPTPT films were always larger when lower k dielectric was employed than when higher k dielectric was used. The higher mobilities obtained when using lower k dielectrics could be attributed to the suppressed distribution of the density of localized states (DOS) near the transport level and to the resulting enhanced electronic coupling between the macromolecules.</P>
Kim, Do Hwan,Shin, Hyeon-Jin,Lee, Hyo Sug,Lee, Jiyoul,Lee, Bang-Lin,Lee, Wi Hyoung,Lee, Jong-Hwa,Cho, Kilwon,Kim, Woo-Jae,Lee, Sang Yoon,Choi, Jae-Young,Kim, Jong Min American Chemical Society 2012 ACS NANO Vol.6 No.1
<P>Molecularly hybridized materials composed of polymer semiconductors (PSCs) and single-walled carbon nanotubes (SWNTs) may provide a new way to exploit an advantageous combination of semiconductors, which yields electrical properties that are not available in a single-component system. We demonstrate for the first time high-performance inkjet-printed hybrid thin film transistors with an electrically engineered heterostructure by using specially designed PSCs and semiconducting SWNTs (sc-SWNTs) whose system achieved a high mobility of 0.23 cm<SUP>2</SUP> V<SUP>–1</SUP> s<SUP>–1</SUP>, no <I>V</I><SUB>on</SUB> shift, and a low off-current. PSCs were designed by calculation of the density of states of the backbone structure, which was related to charge transfer. The sc-SWNTs were prepared by a single cascade of the density-induced separation method. We also revealed that the binding energy between PSCs and sc-SWNTs was strongly affected by the side-chain length of PSCs, leading to the formation of a homogeneous nanohybrid film. The understanding of electrostatic interactions in the heterostructure and experimental results suggests criteria for the design of nanohybrid heterostructures.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2012/ancac3.2012.6.issue-1/nn2041472/production/images/medium/nn-2011-041472_0003.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn2041472'>ACS Electronic Supporting Info</A></P>
Rendering High Charge Density of States in Ionic Liquid-Gated MoS<sub>2</sub> Transistors
Lee, Yeonsung,Lee, Jiyoul,Kim, Sunkook,Park, Ho Seok American Chemical Society 2014 The Journal of Physical Chemistry Part C Vol.118 No.31
<P>We investigated high charge density of states (DOS) in the bandgap of MoS<SUB>2</SUB> nanosheets with variable temperature measurements on ionic liquid-gated MoS<SUB>2</SUB> transistors. The thermally activated charge transport indicates that the electrical current in the two-dimensional MoS<SUB>2</SUB> nanosheets under high charge density state follows the Meyer-Neldel rule. The achieved high charge density allows the surface DOS estimation of MoS<SUB>2</SUB> nanosheets, which have distinct peaks at 0.135 and 0.145 eV below the conduction band, with the largest DOS values of 9.75 × 10<SUP>14</SUP> and 4.33 × 10<SUP>14</SUP> cm<SUP>–2</SUP> eV<SUP>–1</SUP>, respectively. This may represent the monolayer MoS<SUB>2</SUB> nanosheets that coexist with the MoS<SUB>2</SUB> multilayer in the channel area of the ionic liquid-gated MoS<SUB>2</SUB> transistors.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/jpccck/2014/jpccck.2014.118.issue-31/jp5063836/production/images/medium/jp-2014-063836_0005.gif'></P>
Lee, Hyeonseok,Lee, Jong Ik,Park, Hee-Jin,Nam, Su-Yong,Kang, Moon Sung,Chun, Young Tea,Lee, Jiyoul The Electrochemical Society 2019 ECS journal of solid state science and technology Vol.8 No.11
<P>Electrochemiluminescence (ECL) based on a series of electrochemical processes of luminophores has attracted interests as a new light-emitting device platform referred to as the ECL device (ECLD). Here, we investigate the electrical and luminescence properties of ECLD with silver (Ag) electrodes. It is found that ECLD with screen-printed Ag electrodes prepared from carefully selected Ag paste ink could yield higher luminescence than that with thermally-evaporated Ag thin-film electrode. The results indicate that the low-cost large-areal printed ECLD potentially has comparable or surpassing performance to conventional vacuum-processed ECLDs.</P>
Lee Ju Han,Chang Dong Wook,Kim Junghwan,Lee Jiyoul 한국물리학회 2023 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.82 No.5
In contrast to that of conventional inorganic semiconductor materials, the physics of the doping of π-conjugated organic materials is poorly understood. Therefore, this study aimed to investigate the mechanisms underlying the doping of polymer semiconductors. Electrolyte-gated transistors (EGTs) were used to electrochemically modulate the driving force for the molecular-ion doping of π-conjugated-semiconducting polymer flms. Electrochemical transistors were fabricated in which 1-ethyl-3-methylimidazolium-bis(trifuoromethylsulfonyl) ([EMIM][TFSI]) and tetrafuoro-tetracyanoquinodimethane (F4-TCNQ)-doped poly(2,5-bis(3-tetradecylthiophen-2yl)thieon(3,2-b)thiophene) (PBTTT-C14) polymer flms were used as the electrolyte gate medium and conducting channel layer, respectively. The EGTs with F4-TCNQ-doped PBTTT-C14 flms showed conductivity maxima of ~600 S/cm at a critical gate bias, which indicated that there was negative transconductance at gate biases above this threshold. The conductivity maxima of the EGTs with F4-TCNQ-doped PBTTT-C14 flms were caused by excess doping via ion exchange between the [TFSI] anion of the ionic liquid and the F4-TCNQ anion.