High-Performance Near-Infrared-Selective Thin Film Organic Photodiode Based on a Molecular Approach Targeted to Ideal Semiconductor Junctions.

A molecular approach to achieve wide linear dynamic range (LDR) and near-infrared (NIR)-selective thin film organic photodiodes (OPDs) with high detectivity is reported. Comparative studies based on two NIR-selective polymers are systematically investigated: the commercially available poly[(4,4'-bis(2-ethylhexyl)cyclopenta[2,1-b:3,4-b']dithiophene)-alt-(benzo[c][1,2,5]thiadiazole)] (PCPDTBT) and the synthesized poly[(4,4'-(bis(hexyldecylsulfanyl)methylene)cyclopenta[2,1-b:3,4-b']-dithiophene)-alt-(benzo[c][1,2,5]thiadiazole)] (PCPDTSBT). The introduction of sp2-hybridized side chains in the PCPDTSBT structure can improve chain planarity and thus intermolecular interactions, as confirmed by Raman spectroscopy and grazing incidence X-ray diffraction studies. The favorable crystalline orientation of PCPDTSBT leads to enhanced photocurrent and suppressed noise current, compared to that of PCPDTBT, followed by a sharp increase in the specific detectivity of PCPDTSBT-based NIR OPDs by 1.54 × 1012 Jones. The physics behind PCPDTSBT is analyzed employing optical simulation, temperature-dependent junction analyses, and Mott-Schottky analysis. Furthermore, it is found that PCPDTSBT possesses an exceptional nonsaturation photocurrent, which leads to a wide LDR of 128 dB. This study shows the possibility of realizing thin film NIR-selective OPDs using synthetic approaches.

Polyvinyl alcohol covalently grafted CNT for free-standing, flexible, and high-performance thermoelectric generator film.

We introduce a strategic approach to synthesize covalntly cross-linked carbon nanotube (CNT)-polymer nanocomposites, which can be applied as a free-standing and flexible organic thermoelectric generator film. Esterification of polyvinyl alcohol (PVA) to render PVA-COOH followed by an amide reaction with single-walled CNTs (SWCNTs) functionalized with amino groups (SWCNT-NH2) yielded a covalently grafted PVA/SWCNT composite film with an excellent dispersion of SWCNTs within the polymer matrix as confirmed using Fourier-transform infrared spectroscopy and scanning electron microscopy. This amide reaction could be further optimized with the addition of a small amount of Triton™ X-100, which resulted in a better dispersion of SWCNT prior to the amide condensation reaction. Consequently, a covalently cross-linked PVA/SWCNT composite film showed better Seebeck coefficients than those of previously reported non-covalently, physically wrapped polymer/CNT composite films, resulting in a high power factor up to 275 µW m-1 K-2. Furthermore, a covalent amide-linking between PVA and SWCNT yielded a free-standing film (30 × 30 mm) with excellent flexibility and notable shelf stability as confirmed by negligible changes in thermoelectric parameters after bending test for 10 000 times with a bending radius of 2 mm and also shelf stability test in ambient condition without any passivation layer for 30 d.

Synergetic Evolution of Diketopyrrolopyrrole-Based Polymeric Semiconductor for High Reproducibility and Performance: Random Copolymerization of Similarly Shaped Building Blocks.

A new random copolymer consisting of similarly shaped donor-acceptor building blocks of diketopyrrolopyrrole-selenophene-vinylene-selenophene (DPP-SVS) and DPP-thiophene-vinylene-thiophene (DPP-TVT) is designed and synthesized. The resulting P-DPP-SVS(5)-TVT(5) with an equal molecular ratio of the two building blocks produced significantly enhanced solubility when compared to that of the two homopolymers, PDPP-SVS and PDPP-TVT. More importantly, despite the maximum segmental randomness of the PDPP-SVS(5)-TVT(5) copolymer, its crystalline perfectness and preferential orientation are outstanding, even similar to those of the homopolymers thanks to the similarity of the two building blocks. This unique property produces a high charge carrier mobility of 1.23 cm2 V-1 s-1 of PDPP-SVS(5)-TVT(5), as determined from polymer field-effect transistor (PFET) measurements. The high solubility of PDPP-SVS(5)-TVT(5) promotes formulation of high-viscosity solutions which could be successfully processed to fabricate large-areal PFETs onto hydrophobically treated 4 in. wafers. A total of 269 individual PFETs are fabricated. These devices exhibit extremely narrow device-to-device deviations without a single failure and demonstrate an average charge carrier mobility of 0.66 cm2 V-1 s-1 with a standard deviation of 0.064. This is the first study to report on successfully realizing large-areal reproducibility of high-mobility polymeric semiconductors.

Morphology-Driven High-Performance Polymer Transistor-based Ammonia Gas Sensor.

Developing high-performance gas sensors based on polymer field-effect transistors (PFETs) requires enhancing gas-capture abilities of polymer semiconductors without compromising their high charge carrier mobility. In this work, cohesive energies of polymer semiconductors were tuned by strategically inserting buffer layers, which resulted in dramatically different semiconductor surface morphologies. Elucidating morphological and structural properties of polymer semiconductor films in conjunction with FET studies revealed that surface morphologies containing large two-dimensional crystalline domains were optimal for achieving high surface areas and creating percolation pathways for charge carriers. Ammonia molecules with electron lone pairs adsorbed on the surface of conjugated semiconductors can serve as efficient trapping centers, which negatively shift transfer curves for p-type PFETs. Therefore, morphology optimization of polymer semiconductors enhances their gas sensing abilities toward ammonia, leading to a facile method of manufacturing high-performance gas sensors.