Novel Donor-Acceptor Conjugated Benzothiadiazole-based Copolymers Synthesis and Applications for Organic Solar Cell
Date Issued
2009
Date
2009
Author(s)
Chen, Shao-Chieh
Abstract
Polymer solar cells (PSCs) have attracted stong interest in recent years due to the prospect of low cost, solution-based processing and the capability to fabricate flexible devices. To further enhance the power conversion efficiency of 4% achieved from solar cells made of regioregular poly(3-hexylthiophene)/[6,6]-phenyl-C61-butyric acid methyl ester (P3HT/PCBM), a low band gap conjugated polymers with proper energy levels for charge transfer are required. Low optical bandgap conjugated polymers may improve the efficency of organic photovoltaic devices by increasing the absorption in the visible and near infrared region of the solar spectrum. In this master thesis work, I synthesized two new highly soluble and strongly visible-light absorbing alternating polymers using Suzuki coupling polymerization method that are based on 4,7-Bis-(3,4-dimethoxy-thiophen-2-yl)-benzo[1,2,5]thiadiazole monomers: poly[2,7-(9,9-dihexylfluoren)-alt-5,5-(4,7-Bis-(3,4-dimethoxy-thiophen-2-yl)-benzo[1,2,5]thiadiazole] (PF-co-DMOTB) and poly[9-eicosyl-3,6-carbazole-alt-5,5-(4,7-Bis-3,4-dimethoxy-thiophen-2-yl)-benzo[1,2,5]thiadiazole](PC-co-DMOTB). Electrochemical and photophysical studies reveal band gaps of 1.90eV for PF-co-DMOTB and 1.82eV for PC-co-DMOTB, which could effectively harvest broader solar spectrum. The cyclic voltammetry measurements show that the HOMO level of the polymers are -5.19eV for PF-co-DMOTB and -5.70eV for PC-co-DMOTB which are significantly lower than that of P3HT. Bulk heterojuncion photovoltaic devices were fabricated using blends of these copolymers with PCBM as the active layer, ITO-glass as the anode, and aluminum as the cathode. It is observed that the best performing solar cell device which made from polymer PF-co-DMOTB (80 wt% PCBM) delivers an open circuit voltage Voc=0.69 eV, Jsc=1.06 mA cm-2 , FF=0.25 and power conversion efficiency 0.18% under an illumination of A.M.1.5 with an intensity of 100W cm-2.
Subjects
Low band gap
Suzuki coupling
Donor-acceptor
Polymer solar sell
SDGs
Type
thesis
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