Mai Ha Hoang

Highly Photosensitive J‐Aggregated Single‐Crystalline Organic Transistors

Charge-transport phenomena and photoinduced charge generation of organic semiconductors have potential applications in many electronic and optoelectronic devices. Organic fi eld-effect transistors (OFETs) are the most promising electronic devices fabricated using either well-defi ned single crystals (SCs) or thin fi lms as the charge-transporting layers. [ 1–3 ] In particular, soluble organic semiconductors are attracting attention for use in the fabrication of low-cost, large-scale, and practical devices. [ 4 , 5 ]

Unusually High‐Performing Organic Field‐Effect Transistors Based on π‐Extended Semiconducting Porphyrins

Highly conjugated porphyrin derivatives, H(2) TP and ZnTP, are synthesized. J-aggregations of the H-aggregated dimeric porphyrin pairs are clearly observed by their single crystal structures that facilitate slip-stacked charge transport phenomenon. In particular, their SC-FETs show the highest field-effect mobilities of 0.85-2.90 cm(2) V(-1) s(-1) . Furthermore, the ZnTP-based OPT displays a dramatic photoinduced current enhancement with a high photoresponsivity of 22 000 A W(-1) under a very low light intensity (5.6 m W cm(-2) ).

Highly sensitive phototransistor with crystalline microribbons from new π-extended pyrene derivative via solution-phase self-assembly

A new pyrene-cored π-conjugated molecule has been synthesized through Sonogashira coupling reaction. The single-crystalline microribbon-based FET exhibited the highest mobility of 0.7 cm(2) V(-1) s(-1) (I(on)/I(off) > 10(6)). Single-crystalline microribbons were employed to operate in an organic phototransistor (OPT) under very low light intensity (I = 5.6 μW cm(-2)).

High-mobility bio-organic field effect transistors with photoreactive DNAs as gate insulators

Organic-soluble DNAs bearing chalcone moieties were synthesized by using purified natural sodium DNA. In addition to the chalcone-containing DNA homopolymer (CcDNA), a copolymer (CTMADNA-co-CcDNA) was synthesized. They were employed as gate insulators for fabricating organic thin-film transistors. An organic semiconductor (5,5′-(9,10-bis((4-hexylphenyl)ethynyl)anthracene-2,6-yl-diyl)bis(ethyne-2,1-diyl)bis(2-hexylthiophene; HB-ant-THT) was deposited on the photocrosslinked DNA-based gate insulators via a solution process. Interestingly, the resulting TFT devices had extremely high field-effect mobilities, and their corresponding transfer curves indicated low hysteresis. The carrier mobility of the device with HB-ant-THT deposited on the CTMADNA-co-CcDNA gate insulator was the best, i.e., 0.31 cm2 V−1 s−1 (Ion/Ioff=1.0×104).

High-Performance Single-Crystal-Based Organic Field-Effect Transistors from π-Extended Porphyrin Derivatives

Significant research interests have recently emerged for the development of new materials for organic field-effect transistors (OFETs), due to their great promise for use in electronic and optoelectronic applications. Among them, porphyrin derivatives are of particular interest because of their unique properties in photonic and electronics. As a large and flat conjugated tetrapyrrole macrocycle that can be decorated with a variety of metals and substituents, porphyrins have been widely used in solar energy conversion, electron transfer, and artificial photosynthesis, but they have been relatively less exploited as building blocks for the fabrication of OFETs. In fact, most of the organic semiconductors rely on the inherent structural uniqueness of building blocks, such as planarity and p conjugation, and their packing and interactions with adjoining building blocks. In this regard, porphyrins would be one of the best candidates for organic transistors because they could impart multiple interand/or intra-interactions, such as hydrogen bonding, p–p stacking, electrostatic interactions, as well as metal–ligand coordination that could be generated by synthetic modification of the porphyrin framework. Therefore, well-defined crystalline nanoand micro-size structures, such as fibers, rods, ribbons, plates, sheets, cubes, wheels, rings, and grids, are successfully reported. However, the performance of OFET devices based on porphyrin derivatives show relatively low carrier mobility, with a range of 10 6 to 10 1 cm V 1 s , compared with their inorganic analogues, although they have great potentials as mentioned above. Most of the porphyrin OFET devices are based on thin films or crystalline objects prepared by spincoating or vacuum-deposition processes. Therefore, a deeper interpretation of systems has hardly succeeded due to the lack of information about the molecular structure and packing of building blocks at the molecular level that are closely related with the performance of OFET. Most of high performance non-porphyrin organic semiconductors are based on highly ordered molecular packing with strong p–p interactions, showing high crystallinity. However, structural studies of these organic semiconductors have also rarely been exploited due to the difficulties of single-crystal growth even with small conjugated molecules, such as pentacene, rubrene, and anthracene derivatives. Nevertheless, recent achievement on porphyrin-based crystalline OFETs has been successfully demonstrated, but showed relatively low device performance. Herein, we report on single crystalline wires from p-extended porphyrin derivatives TTPH2 and TTPZn, and their unique electronic properties in OFET devices along with single-crystal structures. TTPH2 was readily obtained in relatively high yield (21 %) by using a typical porphyrin condensation reaction between 4-((5-hexylthiophene-2-yl)ethynyl)benzaldehyde and pyrrole in propionic acid. TTPZn was further obtained by metallation of TTPH2 with Zn ACHTUNGTRENNUNG(OAc)2 in 78 % yield (Scheme 1). Detailed synthetic procedures are described in the Supporting Information section (Scheme S1). Cyclic voltammetry analysis of TTPH2 and TTPZn reveals that HOMO, LUMO, and bandgap energy (Eg) are found to be 5.33, 3.40, and 1.93 eV for TTPH2 and 5.28, 3.48, and 1.80 eV for TTPZn, respectively (Table S1). A relatively low bandgap is found in metalloporphyrin TTPZn. Upon layering solutions of TTPH2 and TTPZn in toluene over hexanes and allowing the resulting mixtures to stand over 7–14 days, narrowly dispersed single-crystalline wires were obtained in both cases, which were around 300–500 mm in length and about 4–15 mm in width identified by scanning electron microscopy (SEM) analysis (Figure 1). The single-crystal X-ray structures of TTPH2 and TTPZn are shown in Figure 2. The porphyrin core in TTPH2 is puckered with angles between the N1/N2/N3/N4 plane and each pyrrol ring of 10.88 (N1/C2/C3/C4/C5), 7.28 (N2/C7/C8/ C9/C10), 11.68 (N3/C12/C13/C14/C15), and 7.68 (N4/C17/ C18/C19/C20) as shown in Figure 2 a and b and Figure S1 in the Supporting Information. Interestingly, the porphyrin core in TTPZn is also puckered with angles between the N1/N2/N3/N4 plane and each pyrrol ring of 6.8, 13.3, 9.1, and 10.88 (Figure 2 f and g and Figure S3 in the Supporting Information). Four phenyl rings are tilted from the N1/N2/ [a] Dr. M. H. Hoang, Prof. D. H. Choi, Prof. S. J. Lee Department of Chemistry, Research Institute for Natural Sciences Korea University, 5 Anam-dong, Sungbuk-gu, Seoul 136-701 (Korea) Fax: (+82) 2-924-3141 E-mail : slee1@korea.ac.kr [b] Dr. Y. Kim, Prof. S.-J. Kim Department of Chemistry and NanoScience Ewha Woman s University, Seoul 136-701 (Korea) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201100599.

An Unsymmetrically π-Extended Porphyrin-Based Single-Crystal Field-Effect Transistor and Its Anisotropic Carrier-Transport Behavior

Anisotropic charge transport: Single-crystal organic field-effect transistor devices derived from aggregates of thiophene-appended porphyrins display very high mobility (0.27 cm(2)  V(-1)  s(-1)). This behavior is due to staircase stacking of the porphyrins with distances between layers of 3.17(7) Å. Furthermore, the charge-transport behavior is anisotropic owing to an anisotropic molecular arrangement in the single-crystal microplates.

Enhanced performance of organic photovoltaic devices by photo-crosslinkable buffer layer

AbstractThe performance of organic photovoltaic devices was enhanced by insertion of the photo-crosslinkable buffer layer. This buffer layer was formed by a photo curable precursor with bithiophene and pentadienyl moieties. The fill factor of the device with this buffer layer exceeded 0.7 in the organic photovoltaic cell. The characteristic of the photo-crosslinkable property enabled this buffer layer to be inserted between the hole extraction layer and the active layer, which formed an ohmic contact with both layers. The insertion of the buffer layer induced a 20% enhancement in conversion efficiency by small increases in the short-circuit current and the open-circuit voltage, and a huge increase in the fill factor. This photo-crosslinkable buffer layer acted as a leakage current reducing layer as measured by the reduced dark current. The high crystallinity and smooth surface of this buffer layer resulted in improved surface morphology and internal packing, thus enhanced the fill factor.

Effect of molecular packing of zinc(II) porphyrins on the performance of field-effect transistors

The charge-transport phenomena of organic conjugated materials have been intensively investigated because of the potential applications of these materials in electronics and optoelectronics. Among these applications, organic field-effect transistors (OFETs) fabricated from either thin films or well-defined single crystals as charge-transporting layers are the most promising electronic devices. In this work, the effect of molecular packing on the performance of OFETs is investigated through the fabrication and characterization of devices based on zinc(II) porphyrins TPZ and TBPZ. The field-effect mobility of the transistors is found to increase with decreasing intermolecular distance, attributable to greater overlap of ? orbitals among close-packed molecules and thereby enhance the charge transport.

Synthesis of Gold Nanoparticles Capped with Quaterthiophene for Transistor and Resistor Memory Devices

Recently, the fabrication of nonvolatile memory devices based on gold nanoparticles has been intensively investigated. In this work, we report on the design and synthesis of new semiconducting quaterthiophene incorporating hexyl thiol group (4TT). Gold nanoparticles capped with 4TT (4TTG) were prepared in a two-phase liquid-liquid system. These nanoparticles have diameters in the range 2–6 nm and are well dispersed in the poly(3-hexylthiophene) (P3HT) host matrix. The intermolecular interaction between 4TT and P3HT could enhance the charge-transport between gold nanoparticles and P3HT. Transfer curve of transistor memory device made of 4TTG/P3HT hybrid film exhibited significant current hysteresis, probably arising from the energy level barrier at 4TTG/P3HT interface. Additionally, the polymer memory resistor structure with an active layer consisting of 4TTG and P3HT displayed a remarkable electrical bistable behavior.