Shree Prakash Tiwari
Other affiliations: Nanyang Technological University, Indian Institute of Technology Bombay, Indian Institutes of Technology ...read more
Bio: Shree Prakash Tiwari is an academic researcher from Indian Institute of Technology, Jodhpur. The author has contributed to research in topic(s): Field-effect transistor & Pentacene. The author has an hindex of 24, co-authored 88 publication(s) receiving 1585 citation(s). Previous affiliations of Shree Prakash Tiwari include Nanyang Technological University & Indian Institute of Technology Bombay.
Abstract: A series of highly soluble donor–acceptor (D–A) copolymers containing N-(3,4,5-tri-n-decyloxyphenyl)-dithieno[3,2-b:2′,3′-d]pyrrole (DTP) or N-(2-decyltetradecyl)-dithieno[3,2-b:2′,3′-d]pyrrole (DTP′) as donor and three different acceptors, 4,7-dithien-2-yl-[2,1,3]-benzothiadiazole, 4,9-dithien-2-yl-6,7-di-n-hexyl-[1,2,5]thiadiazolo[3,4-g]quinoxaline and 4,8-dithien-2-yl-2λ4δ2-benzo[1,2-c;4,5-c′]bis[1,2,5]thiadiazole (BThX, X = BTD, TQHx2, BBT, respectively) were synthesized by Stille coupling polymerizations. The optical and electrochemical properties of these copolymers were investigated, along with their use in field-effect transistors and photovoltaic devices. The band gaps (eV) estimated from UV-vis-NIR spectra and electrochemical measurements of the copolymers varied from ca. 1.5–0.5 eV, and were consistent with quantum-chemical estimates extrapolated using density functional theory. Oxidative and reductive spectroelectrochemistry of the copolymers indicated they can be both p-doped and n-doped, and three to four differently colored redox states of the polymers can be accessed through electrochemical oxidation or reduction. The DTP-BThBTD and DTP-BThTQHx2 copolymers exhibited average field-effect hole mobilities of 1.2 × 10−4 and 2.2 × 10−3 cm2/(Vs), respectively. DTP-BThBBT exhibited ambipolar field-effect characteristics and showed hole and electron mobilities of 1.2 × 10−3 and 5.8 × 10−4 cm2/(Vs), respectively. Bulk heterojunction photovoltaic devices made from blends of the copolymers with 3′-phenyl-3′H-cyclopropa[1,9](C60-Ih)[5,6]fullerene-3′-butanoic acid methyl ester (PCBM) (1:3 weight ratio) exhibited average power conversion efficiencies as high as 1.3% under simulated irradiance of 75 mW/cm2.
Abstract: Top-gate bottom-contact field-effect transistors based on solution-processed films of molecules in which two naphthalene-1,8:4,5-bis(dicarboxdiimide)s are bridged by thieno[3,2-b]thiophene, dithien...
Abstract: Low-voltage pentacene organic field-effect transistors (OFETs) with different gate dielectric interfaces are studied and their performance in terms of electrical properties and operational stability is compared. Overall high electrical performance is demonstrated at low voltage by using a 100 nm-thick high-κ gate dielectric layer of aluminum oxide (Al2O3) fabricated by atomic layer deposition (ALD) and modified with hydroxyl-free low-κ polymers like polystyrene (PS), divinyltetramethyldisiloxane-bis(benzocyclobutene) (BCB) (Cyclotene™, Dow Chemicals), and as well as with the widely used octadecyl-trichlorosilane (OTS). Devices with PS and BCB dielectric surfaces exhibit almost similar electrical performance with high field-effect mobilities, low subthreshold voltages, and high on/off current ratios. The higher mobility in pentacene transistors with PS can be correlated to the better structural ordering of pentacene films, as demonstrated by atomic force microscopy (AFM) images and X-ray diffraction (XRD). The devices with PS show good electrical stability under bias stress conditions (VGS = VDS = −10 V for 1 h), resulting in a negligible drop (∼2%) in saturation current (IDS) in comparison to that in devices with OTS (∼12%), and to a very high decay (∼30%) for the devices with BCB.
Abstract: 2,2′-(Benzo[c][1,2,5]thiadiazol-4,7-diyl)-4,4′-dialkyl-bis(4H-dithieno[3,2-b:2′,3′-d]pyrrole) (DTP-BTD-DTP) donor–acceptor–donor (D-A-D) and 4-alkyl-2,6-bis(benzo[c][1,2,5]thiadiazol-4-yl)-4H-dithieno[3,2-b:2′,3′-d]pyrrole (BTD-DTP-BTD) acceptor–donor–acceptor (A-D-A) triads, with or without additional alkylation in the DTP 6- or BTD 7-positions, respectively, have been synthesized using Stille coupling reactions, characterized using UV–vis absorption spectroscopy and electrochemistry, modeled using density functional theory calculations, and used as charge-transport materials in field-effect transistors. The choice of alkyl substitution pattern has only minor effects on the optical and redox behavior but can be used to modify the thermal properties and solubility of these compounds. The D-A-D and A-D-A triads show long-wavelength absorption maxima at 566–588 and 517–521 nm, respectively, in solution. These transitions are attributed to excitation from a delocalized HOMO to a BTD-localized LUMO and, accor...
Abstract: An amphiphilic diketopyrrolopyrrole-based oligothiophene (DPPamphi) has been prepared that displays robust self-assembly behavior in the bulk, in solution, and on surfaces. The material has been used as the active component in organic field-effect transistors and molecular bulk-heterojunction solar cells.
20 Sep 2004
TL;DR: Some of the major milestones along the way are highlighted to provide a historical view of OFET development, introduce the integrated molecular design concepts and process engineering approaches that lead to the current success, and identify the challenges ahead to make OFETs applicable in real applications.
Abstract: The past couple of years have witnessed a remarkable burst in the development of organic field-effect transistors (OFETs), with a number of organic semiconductors surpassing the benchmark mobility of 10 cm2/(V s). In this perspective, we highlight some of the major milestones along the way to provide a historical view of OFET development, introduce the integrated molecular design concepts and process engineering approaches that lead to the current success, and identify the challenges ahead to make OFETs applicable in real applications.
Abstract: Atomic layer deposition (ALD) is gaining attention as a thin film deposition method, uniquely suitable for depositing uniform and conformal films on complex three-dimensional topographies. The deposition of a film of a given material by ALD relies on the successive, separated, and self-terminating gas–solid reactions of typically two gaseous reactants. Hundreds of ALD chemistries have been found for depositing a variety of materials during the past decades, mostly for inorganic materials but lately also for organic and inorganic–organic hybrid compounds. One factor that often dictates the properties of ALD films in actual applications is the crystallinity of the grown film: Is the material amorphous or, if it is crystalline, which phase(s) is (are) present. In this thematic review, we first describe the basics of ALD, summarize the two-reactant ALD processes to grow inorganic materials developed to-date, updating the information of an earlier review on ALD [R. L. Puurunen, J. Appl. Phys. 97, 121301 (2005)], and give an overview of the status of processing ternary compounds by ALD. We then proceed to analyze the published experimental data for information on the crystallinity and phase of inorganic materials deposited by ALD from different reactants at different temperatures. The data are collected for films in their as-deposited state and tabulated for easy reference. Case studies are presented to illustrate the effect of different process parameters on crystallinity for representative materials: aluminium oxide, zirconium oxide, zinc oxide, titanium nitride, zinc zulfide, and ruthenium. Finally, we discuss the general trends in the development of film crystallinity as function of ALD process parameters. The authors hope that this review will help newcomers to ALD to familiarize themselves with the complex world of crystalline ALD films and, at the same time, serve for the expert as a handbook-type reference source on ALD processes and film crystallinity.
Abstract: Side chains in conjugated polymers have been primarily utilized as solubilizing groups. However, these side chains have roles that are far beyond. We advocate using side chain engineering to tune a polymer’s physical properties, including absorption, emission, energy level, molecular packing, and charge transport. To date, numerous flexible substituents suitable for constructing side chains have been reported. In this Perspective article, we advocate that the side chain engineering approach can advance better designs for next-generation conjugated polymers.
TL;DR: This paper presents a new mesoporous-based approach to composites engineering that combines high-performance materials such as cadmium, cadmiferousmaterials, and polymethine with low-cost materials like brass and copper.
Abstract: Xugang Guo,*,† Antonio Facchetti,*,‡,§ and Tobin J. Marks*,‡ †Department of Materials Science and Engineering, South University of Science and Technology of China, No. 1088, Xueyuan Road, Shenzhen, Guangdong 518055, China ‡Department of Chemistry and the Materials Research Center, Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, United States Polyera Corporation, 8045 Lamon Avenue, Skokie, Illinois 60077, United States
Author's H-index: 24