Conjugated polymers for optoelectronics

Doctoral thesis, 2008

The work presented in thesis is divided into two parts; conjugated polymers for light-emitting diodes and conjugated polymers for solar cells. The main focus was on the synthesis and characterisation of the conjugated polymers, together with device preparation and characterisation. The overriding aim has been to correlate the structures of polymers with their properties. A number of polyfluorenes were synthesised for blue and green light-emitting applications. The feasibility of having aromatic substituents on the polyfluorene backbone was studied. Furthermore, a series of polyfluorenes, containing different amounts of triarylamines, were prepared to study the relationship between polymer composition and efficiency of the light-emitting devices. In addition, a bio-organic light emitting device was prepared by using a polyfluorene with polar side chains in conjunction with nano-sized amyloid fibrils. Several monomers and polymers were synthesised using the donor-acceptor-donor (DAD) approach for solar cell applications. By changing the comonomer from fluorene to phenylene and further to an alkoxy-substituted phenylene, the bandgap were reduced because of the increasing electron-donating characteristics of the comonomer. This was shown by both optical absorption and electrochemical measurement. The relationships between structure, morphology, charge mobility, and solar-cell efficiency were studied for six polymers, of which three are polyfluorenes and the remaining three are polyphenylenes. The results show, that rather small differences in molecular structure have large impact on morphology on a micrometer length scale, which in turn influences both charge mobility and solar-cell efficiency.