Synthesis, Characterization and Application of Low Band gap Donor-Acceptor Conducting Polymer Containing Side-Chain Carbazole via Stille Coupling Polymerization
Date Issued
2008
Date
2008
Author(s)
Lu, Ang-Jhih
Abstract
Solar cells based on conducting polymer/nanoparticle hybrid system have recently attracted an ever increasing attention both in academics and industries due especially to their potential to be used in low cost, large area, and roll-to-roll production. To further enhance the power conversion efficiency of 4% achieved from solar cells made of regioregular poly(3-hexyl thiophene)/[6,6]-phenyl C61 butyric acid methyl ester (P3HT/PCBM), new conducting polymers with optimized band energy levels are demonstrated to be one of the key material properties. In this master thesis work, I synthesized a highly soluble quinoxaline/thiophene alternating conducting polymer with hole transport moiety of carbazole as side chain using Stille coupling polymerization method. Various analytical techniques including H-NMR, C13-NMR, FTIR and GPC confirmed a successful synthesis of the constituent monomers [2,5-bis (trimethylstannyl) thiophene and 3-(4-(5,8-dibromo-2-(4-(9-butyl-9H-carbazol-3-yl) phenyl)quinoxalin-3-yl) phenyl)-9 -butyl-9H-carbazole(7)] and the resulting alternating conducting polymer PCPQT. The new conducting polymer PCPQT consists of alternating electron-donating thiophene unit and electron-accepting quinoxaline unit and shows interesting optical properties because of the formation of a charge-transferred (CT) electronic structure along the polymer chain. The polymer is soluble in organic solvents such as tetrahydrofuran and showed an increase in UV-VIS peak from 530nm to 630nm with increasing molecular weight. Powder X-ray diffraction analysis confirms that polydispersed PCPQT exhibits no crystalline order while monodispersed PCPQT shows a crystalline order plane of (100). The CT copolymers are electrochemically active in both oxidation and reduction regions and the cyclic voltammetry measurements show that the HOMO level of the CT polymer is ~5.5eV which is significantly lower than that of P3HT. Preliminary measurements have revealed hole mobilities of about of the pure material and a power conversion efficiency (PCE) up to 0.4% based on the solar cell consisted of PCPQT/PCBM hybrid system under AM 1.5 simulated sun light (100mW/cm2). Notably, the solar cell device made from PCPQT/PCBM exhibits a higher (~0.75V) than that of the conventional P3HT/PCBM one due mainly to the lower HOMO level of PCPQT. Further improvements are anticipated through a rational design of new low band gap quinoxiline/thiophene CT type conducting polymers.
Subjects
low band gap
Suzuki coupling
Stille coupling
carbazole
Donor-acceptor
conducting polymer
Type
thesis
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