title: Synthesis of polymers and small molecules with organic photovoltaic applications
Creators: name: Prasetya, Nor Basid Adiwibawa
Publisher: name: University of Glasgow
Year: 2017
Subjects: subject: Synthesis, polymer, small molecule, organic photovoltaic, subphthalocyanine, thiophene, naphthalimide, benzothiadiazole.

description: This thesis describes the synthesis and characterisation of polymers and small molecules with organic photovoltaic applications. The first chapter of this thesis provides an introduction to organic semiconductors and the working principle of organic photovoltaics. An overview of active materials used in BHJ, as well as examples of some of their performance, is also provided. The second chapter describes the synthesis and characterisation of subphthalocyanine (SubPc) derivatives as active materials for OPV applications. Modifications on the periphery and axial substituents of the SubPcs have been carried out to tailor their physical, optical and electrochemical properties. Among the synthesised SubPcs derivatives, three molecules have been employed as acceptor materials for solution processed BHJ solar cells. The highest performance was achieved when using PTB7 as donor material with a PCE of 3.51%. The third chapter describes the synthesis and characterisation of push-pull small-molecule materials based on the thiophene motif with the objective to explore their application as p-type semiconductors in BHJ devices. The electrochemical studies indicate that the extension of the donor conjugation can reduce the fundamental gap by rising the IP energy level, while the strong electron-accepting moiety can reduce the fundamental gap by lowering the EA energy level. Five molecules have been tested as donor materials for solution processed BHJ solar cells, reporting a PCE of 1.66% as the highest performing donor when blended with PC61BM as the acceptor. The fourth chapter describes the synthesis and characterisation of two naphthalimide-based small molecules bridged with different donor moieties (fluorene and phenothiazine derivatives). Acetylene units were introduced as the bridge between the donor and the acceptor moieties to extend the conjugation and ensure the planarity of the synthesised molecules. Based on their energy levels, the two molecules can be employed as potential donor and acceptor materials for solution processed BHJ devices and will be tested in the future. Finally, the fifth chapter describes the syntheses of polythiophenes and benzothiadiazole-based copolymers with the objective to explore their application as donor materials in BHJ devices. Two polythiophene polymers were successfully synthesised and characterised. One of the polythiophene polymers was comprised of a glycol side chain, namely P3(TEG)T, showing good solubility, offering a wide range selection of solvents for BHJ devices fabrication. Another polythiophene was synthesised via Huisgen cycloaddition reaction between ethynyl end-capped P3HT polymer and a naphthalene glycol derivative containing an azide end group. The polymer was successfully isolated with a narrow dispersity (Ð). The studies indicate that additional naphthalene glycol moiety does not change the thermal, optical and electrochemical properties of the polymer. Two polymers containing BT moiety were also synthesised and characterised. All the polymers have a low energy gap with IP and EA values above those of fullerene derivatives. As a result, the polymers could potentially act as an efficient p-type semiconductor in BHJ solar cells. In this work, the polymer P3(TEG)T has been tested its performance in BHJ solar cell devices, displaying very poor performance. The low efficiency was associated with low charge-mobility indicated from low JSC value.