Synthesis and characterization of novel quinoxalinebased and thieno[3,4-c]pyrrole-4,6-dione-based conjugated polymers and their applications in organic electronics

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2017
Karabağ, Aliekber
In this thesis novel quinoxaline-based and thieno[3,4-c]pyrrole-4,6-dione (TPD)- based monomers were firstly synthesized. Structural analysis of each material synthesized was performed with Nuclear Magnetic Resonance (NMR) Spectroscopy and High-Resolution Mass Spectroscopy (HRMS). Two novel quinoxaline-based monomers were polymerized with electrochemical and/or chemical polymerization whereas TPD-based monomer was polymerized with benzodithiophene-based acceptor via Stille coupling polycondensation reaction. Molecular weight of the polymers was determined by Gel Permeation Chromatography (GPC). The electrochemical behaviors of monomers were studied with Cyclic Voltammetry (CV); on the other hand, the electrochromic properties of polymers were studied with spectroelectrochemical, colorimetric and kinetic studies. ELEC-PQUIN-12C-TH showed both n-dopable/p-dopable and multi-chromic characteristics. In literature, the polymers having such property is rare; therefore, they are used for special purposes such as display systems and smart windows. On the other vi hand, ELEC-PQUIN-2OD-ED and CHEM-PQUIN-2OD-ED showed just p-dopable characteristics. Although such properties were common for almost all conjugated polymers, the polymers showing green color in their neutral state and transmissive grey color in their oxidized state are rare in literature. This kind of polymers having one of the complementary colors (RGB colors) in their neutral states and transmissive grey in their oxidized states are interested in many applications like simple display devices. In addition, both ELEC-PQUIN-2OD-ED and CHEM-PQUIN-2OD-ED displayed greater optical contrasts in the visible region (43% at 728 nm and 45% at 730 nm) compared to the state of the art polymer, PDOPEQ. Furthermore, chemically synthesized quinoxaline-based homopolymer with EDOT side units showed excellent solubility in common organic solvents, especially in CHCl3. To make CHEMPQUIN-2OD-ED soluble in such solvents, it was designed with a long-branched alkyl chain. Since ELEC-QUIN-12C-TH, ELEC-PQUIN-2OD-ED and CHEM-PQUIN- 2OD-ED have promising electrochemical and electrochromic characteristics, they can be easily integrated into today's electrochromic technology even the new generation electrochromic devices. An acceptor unit containing TPD was designed with selenophene building blocks since polymers that utilizes with selenophene side units result in polymers with low band gap energy (<2.0 eV) and broad absorptions with covering NIR region. There is only one report of selenophene attached TPD unit being used in organic solar cells. A number of possible novel polymers can be synthesized using this material. Therefore, selenophene was integrated into TPD central unit as a side unit. In literature, BTA and BDT are also known as promising materials for preparing organic solar cells with a high efficiency. Therefore, novel random copolymer including TPD, BTA and BDT materials were designed and synthesized via Stille coupling. This polymer was then used as donor whereas PCBM, the common and soluble derivative of fullerene was used as acceptor in preparation of organic solar cells. Thickness and morphological properties of poly(TPD-BTA-BDT):PC71BM were investigated and based on these results suitable solar cell devices (ITO/PEDOT:PSS/poly(TPD-BTABDT):PC71BM/LiF/Al) were prepared. Current-Voltage (I-V) properties of each cell were also examined. All solar cell studies were done by using solar simulators in a nitrogen-filled glovebox system (moisture <0.1 ppm; oxygen <0.1 ppm). Data obtained from photovoltaic device was used to calculate Power Conversion Efficiency (PCE) measured under standard AM1.5 G illumination (100mW.cm-2 ). Without going through the optimization process which has significant effect on PCEs, the material showed 3.0% efficiency. This is a highly promising result and the optimizations are currently underway in our laboratories.

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Citation Formats
A. Karabağ, “Synthesis and characterization of novel quinoxalinebased and thieno[3,4-c]pyrrole-4,6-dione-based conjugated polymers and their applications in organic electronics,” M.S. - Master of Science, Middle East Technical University, 2017.