Green Solvent Processable Conjugated Polymers for Organic Photovoltaics

Author: Xun Pan

Pan, Xun, 2018 Green Solvent Processable Conjugated Polymers for Organic Photovoltaics, Flinders University, College of Science and Engineering

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Organic photovoltaics (OPVs) have experienced rapid development during the past decade, showing great potential in the utilisation of renewable solar energy. To realise the commercially competitive manufacturing of OPVs, tremendous efforts have been put into the design of novel conjugated materials and device engineering. However, the fabrication of OPVs, especially the deposition of photoactive layer is mainly processed using halogenated solvents, which is counterproductive to the environmentally friendly goal of OPVs. The harmfulness of halogenated solvents is one of the hurdles to overcome before the high performing OPVs can be transferred from a lab-scale to an industrial scale fabrication. Hence, urgent development of green solvent processable conjugated systems is required to realise the environmentally benign fabrication of solar cells.

This thesis is dedicated primarily to the study of water/ethanol processable photoactive materials in two main methodologies:

1. Design, synthesis and characterisation of water/ethanol soluble p-type conjugated polymers based on side-chain engineering.

2. Design, preparation and characterisation of water-dispersed conjugated nanoparticles (NPs) from water-insoluble donor-acceptor active materials.

A series of new polymers were successfully synthesised utilising tertiary amine and pyridine substituents, presenting superb processibility using water/ethanol. The comprehensive characterisation of the functionalized polymers reveals the influence of side-chain properties and their content on the morphology of the bulk-heterojunction (BHJ) layer. The interaction between the functionalized polymers and fullerene derivative as well as polymer-anode interface was systematically studied. Among all the water/ethanol soluble p-type polymers, TQ1-50P4, which contains 50% of pyridine side groups, showed the most promising results, as 1.33% of PCE was achieved from TQ1-50P4 based OPVs.

In order to achieve water processibility for the deposition of active layers based on existing conjugated materials, water-dispersed NPs were prepared using two pre-established methods (miniemulsion and precipitation method). Efforts have been put into the elimination and replacement of the commonly used insulating surfactant, aiming to improve the efficiency of NP based OPVs. An environmentally friendly preparation of NPs was demonstrated, which eliminates the usage of halogenated solvent in both NP preparation and device fabrication, presenting promising photovoltaic performance (1.65% PCE). The results provide a guideline for developing green preparation of NPs for high performing OPVs.

Keywords: environment-friendly, conjugated polymers, side-chain engineering, water-dispersed nanoparticles.

Subject: Chemistry thesis

Thesis type: Doctor of Philosophy
Completed: 2018
School: College of Science and Engineering
Supervisor: Professor Mats Andersson