Liquid Crystal-Gated-Organic Field-Effect Transistors with In-Plane Drain–Source–Gate Electrode Structure

We report planar liquid crystal-gated-organic field-effect transistors (LC-<i>g</i>-OFETs) with a simple in-plane drain–source–gate electrode structure, which can be cost-effectively prepared by typical photolithography/etching processes. The LC-<i>g</i>-OFET devices were fabricated by forming the LC layer (4-cyano-4′-pentylbiphenyl, 5CB) on top of the channel layer (poly­(3-hexylthiophene), P3HT) that was spin-coated on the patterned indium–tin oxide (ITO)-coated glass substrates. The LC-<i>g</i>-OFET devices showed p-type transistor characteristics, while a current saturation behavior in the output curves was achieved for the 50–150 nm-thick P3HT (channel) layers. A prospective on/off ratio (>1 × 10³) was obtained regardless of the P3HT thickness, whereas the resulting hole mobility (0.5–1.1 cm²/(V s)) at a linear regime was dependent on the P3HT thickness. The tilted ordering of 5CB at the LC-P3HT interfaces, which is induced by the gate electric field, has been proposed as a core point of working mechanism for the present LC-<i>g</i>-OFETs

Stable Protein Device Platform Based on Pyridine Dicarboxylic Acid-Bound Cubic-Nanostructured Mesoporous Titania Films

Here we shortly report a protein device platform that is extremely stable in a buffer condition similar to human bodies. The protein device platform was fabricated by covalently attaching cytochrome <i>c</i> (cyt <i>c</i>) protein molecules to organic coupler molecules (pyridine dicarboxylic acid, PDA) that were already covalently bound to an electron-transporting substrate. A cubic nanostructured mesoporous titania film was chosen as an electron-transporting substrate because of its large-sized cubic holes (∼7 nm) and highly crystalline cubic titania walls (∼0.4 nm lattice). Binding of PDA molecules to the mesoporous titania surface was achieved by esterification reaction between carboxylic acid groups (PDA) and hydroxyl groups (titania) in the presence of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) mediator, whereas the immobilization of cyt <i>c</i> to the PDA coupler was carried out by the EDC-mediated amidation reaction between carboxylic acid groups (PDA) and amine groups (cyt <i>c</i>). Results showed that the 2,4-position isomer among several PDAs exhibited the highest oxidation and reduction peak currents. The cyt <i>c</i>-immobilized PDA-bound titania substrates showed stable and durable electrochemical performances upon continuous current–voltage cycling for 240 times (the final current change was less than 3%) and could detect superoxide that is a core indicator for various diseases including cancers

Strong Composition Effects in All-Polymer Phototransistors with Bulk Heterojunction Layers of p‑type and n‑type Conjugated Polymers

We report the composition effect of polymeric sensing channel layers on the performance of all-polymer phototransistors featuring bulk heterojunction (BHJ) structure of electron-donating (p-type) and electron-accepting (n-type) polymers. As an n-type component, poly­(3-hexylthiopehe-<i>co</i>-benzothiadiazole) end-capped with 4-hexylthiophene (THBT-4ht) was synthesized via two-step reactions. A well-studied conjugated polymer, poly­(3-hexylthiophene) (P3HT), was employed as a p-type polymer. The composition of BHJ (P3HT:THBT-4ht) films was studied in detail by varying the THBT-4ht contents (0, 1, 3, 5, 10, 20, 30, 40, and 100 wt %). The best charge separation in the P3HT:THBT-4ht films was measured at 30 wt % by the photoluminescence (PL) study, while the charge transport characteristics of devices were improved at the low THBT-4ht contents (<10 wt %). The photosensing experiments revealed that the photosensivity of all-polymer phototransistors was higher than that of the phototransistors with the pristine P3HT layers and strongly dependent on the BHJ composition. The highest (corrected) responsivity (<i>R</i>_C) was achieved at 20 wt %, which can be attributable to the balance between the best charge separation and transport states, as investigated for crystal nanostructures and surface morphology by employing synchrotron-radiation grazing-incidence wide-angle X-ray scattering, high-resolution/scanning transmission electron microscopy, and atomic force microscopy

2,2′-Bis(1,3,4-thiadiazole)-Based π‑Conjugated Copolymers for Organic Photovoltaics with Exceeding 8% and Its Molecular Weight Dependence of Device Performance

A series of novel π-conjugated copolymers based on 2,2′-bis­(1,3,4-thiadiazole) (BTDz) have been developed. Among them, the BTDz-based donor–acceptor alternating copolymer with the (<i>E</i>)-1,2-di­(3-(2-ethyl­hexyl)­thiophene)­vinylene donor unit (PBTDzTV) exhibited a high solubility and high crystallinity. PBTDzTVs favorably self-assembled, forming face-on and edge-on multibilayer structures in thin nanoscale films. The relative volume fractions of these structures varied depending on the polymer’s molecular weight. The higher molecular weight polymer formed a higher volume fraction of the face-on structure; in particular, the polymer with a 26.6 kDa of number-average molecular weight made only the face-on structure. The device performance was improved as the polymer molecular weight and the volume fraction of the face-on structure increased. The bulk-heterojunction photovoltaic device based on PBTDzTV:PC₇₁BM demonstrated the high power conversion efficiency (PCE) of 8.04% when the device was fabricated with the highest molecular weight polymer having the face-on structure

Light-Induced Open Circuit Voltage Increase in Polymer Solar Cells with Ternary Bulk Heterojunction Nanolayers

We report a light-induced open circuit voltage (<i>V</i>_OC) increase in polymer solar cells with ternary bulk heterojunction (BHJ) layers that are composed of poly­(3-hexylthiophene) (P3HT), poly­[(4,8-bis­(2-ethylhexyloxy)-benzo­[1,2-b:4,5-b′]­dithiophene)-2,6-diyl-<i>alt</i>-(N-2-ethylhexylthieno­[3,4-<i>c</i>]­pyrrole-4,6-dione)-2,6-diyl]] (PBDTTPD), and [6,6]-phenyl-C₆₁-butyric acid methyl ester (PC₆₁BM). The ternary BHJ layers were prepared by varying the composition of donor polymers at a fixed ratio (1:1 by weight) of donor (P3HT + PBDTTPD) to acceptor (PC₆₁BM). Results showed that <i>V</i>_OC was gradually increased under continuous illumination of solar light (100 mW/cm²) for ternary solar cells, whereas no <i>V</i>_OC increase was measured for binary solar cells without PBDTTPD. As a consequence, the power conversion efficiency (PCE) of ternary solar cells (except the highest PBDTTPD content) was rather higher after solar light illumination for 10 h, even though the binary solar cell exhibited significantly lowered PCE after 10 h illumination. The <i>V</i>_OC increase has been attributed to the lateral phase segregation between P3HT and PBDTTPD domains in the ternary BHJ layers under continuous illumination of solar light, as evidenced from the analysis result by Raman spectroscopy, atomic force microscopy, transmission electron microscopy, and synchrotron radiation grazing-incidence angle X-ray diffraction measurements

Hybrid Phototransistors Based on Bulk Heterojunction Films of Poly(3-hexylthiophene) and Zinc Oxide Nanoparticle

Hybrid phototransistors (HPTRs) were fabricated on glass substrates using organic/inorganic hybrid bulk heterojunction films of p-type poly­(3-hexylthiophene) (P3HT) and n-type zinc oxide nanoparticles (ZnO_<i>NP</i>). The content of ZnO_<i>NP</i> was varied up to 50 wt % in order to understand the composition effect of ZnO_<i>NP</i> on the performance of HPTRs. The morphology and nanostructure of the P3HT:ZnO_<i>NP</i> films was examined by employing high resolution electron microscopes and synchrotron radiation grazing angle X-ray diffraction system. The incident light intensity (<i>P</i>_IN) was varied up to 43.6 μW/cm², whereas three major wavelengths (525 nm, 555 nm, 605 nm) corresponded to the optical absorption of P3HT were applied. Results showed that the present HPTRs showed typical p-type transistor performance even though the n-type ZnO_<i>NP</i> content increased up to 50 wt %. The highest transistor performance was obtained at 50 wt %, whereas the lowest performance was measured at 23 wt % because of the immature bulk heterojunction morphology. The drain current (<i>I</i>_D) was proportionally increased with <i>P</i>_IN due to the photocurrent generation in addition to the field-effect current. The highest apparent and corrected responsivities (<i>R</i>_A = 4.7 A/W and <i>R</i>_C = 2.07 A/W) were achieved for the HPTR with the P3HT:ZnO_<i>NP</i> film (50 wt % ZnO_<i>NP</i>) at <i>P</i>_IN = 0.27 μW/cm² (555 nm)

All-Polymer Solar Cells with Bulk Heterojunction Films Containing Electron-Accepting Triple Bond-Conjugated Perylene Diimide Polymer

A triple bond-linked perylene diimide (PDI) conjugated polymer, poly­{[<i>N</i>,<i>N</i>′-dioctylperylene-3,4,9,10-bis­(dicarboximide)-1,7­(6)-diyl]-<i>alt</i>-[(2,5-bis­(2-ethylhexyl)-1,4-phenylene)­bis­(ethyn-2,1-diyl]} (PDIC8-EB), was examined as an electron-accepting component in all-polymer solar cells. As an electron-donating component, poly­[4,8-bis­[(2-ethylhexyl)­oxy]­benzo­[1,2-b:4,5-b′]­dithiophene-2,6-diyl]­[3-fluoro-2-[(2-ethylhexyl)­carbonyl]­thieno­[3,4-<i>b</i>]-thio­phenediyl] (PTB7) and poly­[4,8-bis­(5-(2-ethylhexyl)­thiophen-2-yl)­benzo­[1,2-b:4,5-b′]­dithiophene-<i>alt</i>-3-fluorothieno­[3,4-<i>b</i>]­thiophene-2-carboxylate] (PTB7-Th) were introduced in order to investigate the feasibility of PDIC8-EB because of their similarity. Results showed that the power conversion efficiency (PCE) was higher for the PTB7-Th:PDIC8-EB solar cells (PCE = 3.58%) than the PTB7:PDIC8-EB solar cells (PCE = 2.81%). The better performance of the PTB7-Th:PDIC8-EB solar cells has been attributed to the formation of a well-defined nanodomain morphology in the PTB7-Th:PDIC8-EB bulk heterojunction layer, as measured with transmission electron microscopy (TEM), atomic force microscopy (AFM), and synchrotron radiation grazing incidence X-ray diffraction (GIXD)

Broadband pH-Sensing Organic Transistors with Polymeric Sensing Layers Featuring Liquid Crystal Microdomains Encapsulated by Di-Block Copolymer Chains

We report broadband pH-sensing organic field-effect transistors (OFETs) with the polymer-dispersed liquid crystal (PDLC) sensing layers. The PDLC layers are prepared by spin-coating using ethanol solutions containing 4-cyano-4′-pentyl-biphenyl (5CB) and a diblock copolymer (PAA-<i>b</i>-PCBOA) that consists of LC-philic block [poly­(4-cyano-biphenyl-4-oxyundecyl acrylate) (PCBOA)] and acrylic acid block [poly­(acrylic acid) (PAA)]. The spin-coated sensing layers feature of 5CB microdomains (<5 μm) encapsulated by the PAA-<i>b</i>-PCBOA polymer chains. The resulting LC-integrated-OFETs (PDLC-<i>i</i>-OFETs) can detect precisely and reproducibly a wide range of pH with only small amounts (10–40 μL) of analyte solutions in both static and dynamic perfusion modes. The positive drain current change is measured for acidic solutions (pH < 7), whereas basic solutions (pH > 7) result in the negative change of drain current. The drain current trend in the present PDLC-<i>i</i>-OFET devices is explained by the shrinking-expanding mechanism of the PAA chains in the diblock copolymer layers