Soluble processable organic semiconductors offer several advantages over their traditional inorganic counterparts. They can be processed by a variety of large-area techniques, are lightweight, robust and flexible. Furthermore, their properties can be readily tuned by modifications to the chemical structure of the semiconductor. This influences both the fundamental optoelectronic properties, such as band gap and energy levels, as well as the physical properties such as molecular aggregation and thin-film morphology.
This work is focussed upon the potential of 1,1’-binaphthyl (BN) derivatives as building blocks in the development of new materials for organic photovoltaics (OPV) applications. Due to steric interaction between the protons in the 8,8’ position, BN is inherently twisted with a torsional angle of about 90°. Incorporation of BN into organic semiconducting materials was therefore expected to lead to non-planar materials with suppressed crystallisation in the solid state. This strategy was explored for novel acceptor materials for organic solar cells, in which large scale crystallisation can lead to detrimental device performance and stability. Two classes of BN cored semiconductors were synthesised, containing either diketopyrrolopyrrole or rhodanine end-groups with varying alkyl sidechains. Their optoelectronic performance is reported, along with preliminary device data.
Functionalised BN derivatives also exhibit atropisomerism, and their incorporation into organic semiconducting polymers and small molecules was also explored as an approach to afford chirally active, electronically functional materials.