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Title: Development of new conjugated polymers for organic photovoltaics
Author: Murad, Ary
ISNI:       0000 0004 6061 360X
Awarding Body: University of Sheffield
Current Institution: University of Sheffield
Date of Award: 2017
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Polymer solar cells (PSCs) have received substantial consideration as clean and renewable energy sources due to their advantages such as solution-processing, low cost, lightweight and mechanically flexible devices. In the last few years, the power conversion efficiency of bulk heterojunction solar cells has increased dramatically reaching up to 10% recently. This dissertation focuses on two types of conjugated polymers, thermocleavable polymers and donor-acceptor (D-A) polymers. Three novel thermocleavable polymers, 35, 36 and 37 were prepared via the Stille polymerisation. 35 and 36 consisting of bithiophene and tetrathiophene as the donor units and secondary phthalate ester as the acceptor units. 37 contains fluorene flanked by thienyl groups as the donor units and secondary phthalate ester as the acceptor units. The optical band gaps (Eg) of the polymers are between 2.11 and 2.58 eV. After thermal treatment, the band gaps of the polymers have decreased to between 1.86 and 2.14 eV. A series of D-A copolymers including benzothiadiazole dicarboxylic imide (BTDI) as acceptor units with different donor units were synthesised. Two different alkyl side chains (3,7-dimethyloctyl vs n-octyl) were anchored to the BTDI units in order to investigate the effect of these alkyl substituents on the solubility, molecular weights, optoelectronic properties, thermal and structural properties of the polymers. Four copolymers, 76, 77, 78 and 79 based on 2,7-fluorene or 2,7-dibenzosilole were synthesised via Suzuki polymerisation. Dibenzosilole-based polymers have slightly lower Eg relative to their fluorene-based analogues. Another four copolymers, 104, 105, 106 and 107 including 2,7-carbazole were also synthesised via Suzuki polymerisation. Two fluorine atoms were incorporated at the 3,6-positions of 2,7-carbazole units to investigate the impact of fluorine upon the optoelectronic properties, thermal and structural properties of the polymers. The Eg of fluorinated copolymers are slightly higher than non-fluorinated counterparts. Two copolymers, 109 and 110 containing 2,6-anthracene were also prepared through Suzuki polymerisation. Both polymers have low Eg of 1.66 eV. A series of copolymers, 134, 135, 136 and 137 containing cyclopentadithiophene (CPDT) were prepared. 134 was prepared by Suzuki polymerisation, while the other three copolymers were prepared by direct arylation polymerisation. The Eg of the polymers are between 1.32 and 1.43 eV. The final two alternating copolymers of dithienosilole (DTS), 144 and 145, were prepared via Stille polymerisation. Both polymers have low Eg around 1.4 eV. Copolymers based on fluorene, dibenzosilole, carbazole and anthracene units have deep HOMO energy levels about –5.5 eV. However, the HOMO energy levels of the copolymers containing CPDT and DTS units are significantly shifted upward to around (–5.1 to –5.2 eV). The LUMO levels of the copolymers are between –3.4 and –3.5 eV. All polymers exhibit good thermal stability with decomposition temperatures surpassing 310 °C. Powder X-ray diffraction studies have shown that all polymers have an amorphous nature in solid state.
Supervisor: Iraqi, Ahmed Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available