Conjugated Polymers in Thermoelectric Composites and Small Molecules for High Light Absorptivity

Over the past several decades with increasing of global energy demand, thermoelectric materials have gained considerable attention due to their unique ability to directly convert heat to electricity. In addition to inorganic semiconductors, polymers are potential candidates for high-performance thermoelectric applications due to their intrinsic advantages such as low thermal conductivity, solution processability, and roll-to-roll production, lightweight, and flexible thermoelectric modules. This thesis provides an insight into the emerging field of organic thermoelectrics, more specifically, thermoelectric power generation based on the composites of conducting polymers (MEH-PPV, P3HT and PEDOT:PSS) and carbon nanotubes (SWNT, SWNT-COOH, SWNT-OH and MWNT). A substantial portion of my work at the graduate level has involved the composite materials of conductive polymers and carbon nanotubes (CNTs) for use in organic thermoelectrics (TE). This work comprised multiple iterations to test effects of chain length (molecular weight) and regioregularity, amount and type of CNT added, sample fabrication solvent, and doping duration led to substantial optimization of the TE power factors. A power factor of 148 μW m-1 K-2 was obtained in the optimized sample preparation with rr-P3HT-Rieke/50%SWnNT which is quite competitive with the PFs mentioned in section 2.3. Besides polymers, I also investigated TE properties of cross-linked network structures established from UV curable small molecules with CNTs. A variety of distinct morphological architectures -- consistent with differences in TE performances -- have been observed. I described the synthesis of new pyridinium and extended viologen molecules capturing light in the visible portion of the solar spectrum with high molar extinction coefficient (~22,000 to 278,000 M-1 cm-1) by means of intramolecular charge transfer (ICT), using electron-donor and electron-accepter groups linked through π-conjugation. Also, these compounds exhibited solvatochromic properties in absorption and emission spectra with respect to the ICT band

Recognition-Mediated Assembly of Quantum Dot Polymer Conjugates with Controlled Morphology

We have demonstrated a polymer mediated “bricks and mortar” method for the self-assembly of quantum dots (QDs). This strategy allows QDs to self-assemble into structured aggregates using complementary three-point hydrogen bonding. The resulting nanocomposites have distinct morphologies and inter-particle distances based on the ratio between QDs and polymer. Time resolved photoluminescence measurements showed that the optical properties of the QDs were retained after self-assembly

A narrow range multielectrochromism from 2,5-di-(2-thienyl)-1H-pyrrole polymer bearing pendant perylenediimide moiety

WOS: 000346543200016A new 2,5-di-(2-thienyl)-1H-pyrrole (SNS) moiety containing perylenediimide (PDI) acceptor as pendant side chain has been synthesized for an electroactive monomer and then directly deposited onto ITO/glass surface via electrochemical polymerization process. The observed electronic interaction only at the excited state due to the presence of phenylene spacer between SNS-donor and PDI-acceptor moiety leads to efficient fluorescence quenching. This charge separation behavior was also proved by theoretical DFT calculations. Thin films of the polymer electropolymerized onto transparent electrode exhibited ambipolar multi-electrochromic behavior including purple, violet-red-khaki-blue colors in both anodic and cathodic regime only between -1.2 and 1.0 V. We further demonstrated that this polymer film has a high contrast ratio (Delta T = 45% at 900 nm), a faster response (0.5 s), high coloration efficiency (254 cm(2) C-1) and retained its performance by 92% even after 5000 cycles. (C) 2014 Elsevier Ltd. All rights reserved.Canakkale Onsekiz Mart University Grants CommissionCanakkale Onsekiz Mart University [2010/99]We gratefully acknowledge the supports from Canakkale Onsekiz Mart University Grants Commission (Project Number: 2010/99)

A Novel Near-IR Effective Pyrene-Based Donor-Acceptor Electrochrome

In this work, a novel donor-acceptor electrochromic monomer (3HTP), containing a pyrene subunit connected to a quinoxaline acceptor bridge, is synthesized. The corresponding polymer, poly-(3HTP), is directly deposited onto an indium tin oxide (ITO)/glass surface via an electrochemical process. Atomic force microscopy (AFM) images reveal that the electrochemically deposited poly-(3HTP) has a smooth surface due to self-assembly of the planar pyrene subunit. Electrochemical and optical properties are investigated via cyclic voltammetry and UV-vis absorption measurements. The polymer film shows a multielectrochromic feature at both anodic and cathodic regimes. Poly-(3HTP) exhibits a strong near-infrared (NIR) absorption at the oxidized state with an optical contrast of 88% (at 1800 nm), a very fast response time of 0.5 s and fast switching times, and long-term stability. Density functional theory calculations reveal that the molecule has a high planarity, and the NIR absorption arises from a strong intramolecular charge transfer from the polymer backbone to the planar pyrene subunit

Direct photopatterning of light-activated gold nanoparticles

Photoactivatable gold NPs were patterned via photolithography. In this approach, charge reversal of the ligands on NPs upon UV irradiation induces crosslinking to generate stable NP patterns

Thermoelectric Enhancement by Compositing Carbon Nanotubes into Iodine-Doped Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]

Free-standing iodine-doped composite samples of poly­[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) with carbon nanotubes (NTs) showed thermoelectric (TE) power factors (PFs) up to 33 μW·m^–1·K^–2 after optimizing multiple factors, including: (1) sample fabrication solvent, (2) doping time, (3) average MEH-PPV molecular weight, (4) NT fraction in the composite, and (5) use of single-wall versus multi-wall nanotubes (SWNT and MWNT, respectively). Composite fabrication from halogenated solvents gave the best TE performance after iodine doping times of 2–4 h; performance drops substantially in ∼20 h doped samples. TE performance dropped after at least 24 h of removal from iodine vapor but was fully restored upon re-exposure to the dopant. Longer-chain MEH-PPV gave not only mechanically stronger films but also higher PFs in doped SWNT composites. MWNT composites gave low PFs, attributed to poor NT dispersion. Scanning electron microscopy showed increasingly extensive network formation as NT fraction increased in the composites; this phase separation provides charge transport pathways that improve thermoelectric PFs. The results support a strategy of producing phase-separated materials having both electrical conduction enhanced regions and Seebeck thermopower retaining regions to maximize organic TE response