Synthesis and characterization of novel low bandgap conjugated polymers containing fused-ring and accept moieties

Abstract

The most common way of harnessing solar energy currently is through the use of crystalline silicon photovoltaic (PV). However, the production of silicon based PV is too costly for widespread use. This high cost together with low efficiency also makes large scale solar power plant cost and space ineffective. Organic polymer PVs are seen as a cheaper alternative. Conjugated polymer in particular had attracted more attention because of its mechanical and electrical properties.

In this project, a novel low bandgap conjugated polymers based on dithieno[3,2-b:2’,3’-d]pyrrole (DTP) and pyridine will be synthesised. The purpose of this project is to investigate the properties of different N-alkyl functional DTP and also effect of different positions of substituent in the pyridine group.

A series of four different polymers was synthesised and characterised by their structural, thermal, optical and electrical properties. Structural properties were characterised using nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC) while thermal properties were characterised using differential scanning calorimeter (DSC) and thermogravimetric analyzer (TGA). Ultraviolet-visible (UV-Vis) and photoluminescence (PL) were used for optical properties and cyclic voltammetry (CV) was used to characterise electrical properties.

It was found that Poly[N-(dodecyl)-DTP-2,5-Pyridine] had the best characteristic among the polymers synthesised in this project to be further developed into a organic photovoltaic material. (Decomposition temperature, Td = 327 °C, Optical bandgap, Eg,opt = 2.14 eV Electrical bandgap, Eg,elec = 1.34)