Design, synthesis and characterisation of conjugated polymers containing reactive functionality for organic photovoltaics

The nanoscale morphology of the active layer in organic photovoltaic devices is critical to their performance. Blend morphologies can be manipulated by using a variety of additives, co-solvents and by thermal annealing. However, one crucial issue for any organic photovoltaic device is operational lifetime, which is largely dictated by changes in the active layer morphology. Such changes may be due to reordering of the polymer material, or diffusion and aggregation of fullerene derivatives to a more thermodynamically stable state. This reordered structure can potentially have detrimental effect by losses in interfacial surface area and an increase in exciton recombination. Many novel polymers are designed without this consideration and may be susceptible to this type of degradation. Herein, we explore a variety of approaches to stabilise the blend morphology, principally by the incorporation of various reaction functionalities onto the polymer backbone. The three main areas which have been investigated are; varying of acceptor strengths, chain end modifications with various crosslinking chemistries and thermally cleavable leaving groups. Firstly, poly(dithienogermole-benzothiadiazole) analogues are synthesised to investigate how changes to the acceptor strength of the D-A co-polymers will affect the bulk heterojunction morphology and polymer performance. Then the synthesis and functionalisation of benzotriazole in poly(cyclopentadithiophene-benzotriazole) with alkyl bromine crosslinking groups and thienopyrroledione in poly(dithienogermole-thienopyrroledione), with both alkyl bromide & alkyl oxetane crosslinking groups was investigated. Further studies will investigate the effects on material and optoelectronic properties as well as device performance in OPV and suitability of additives with crosslinking. Lastly, we explore the incorporation of thermal cleavable BOC groups on thienopyrroledione, in poly(cyclopentadithiophene-thienopyrroledione), the deprotection of Boc in polymeric materials and its effects on material and optoelectronic properties.Open Acces