Tuning exciton diffusion in organic optoelectronic materials

Exciton diffusion is one of the crucial processes in operation of organic optoelectronic devices such as organic solar cells, photoreceptors, light emitting, upconverting or other devices, therefore manipulation of exciton diffusion length is of high importance. The dissertation is aimed at achieving tunability of exciton diffusion in organic solid films of triphenylamine (TPA) and 9,10-diphenylanthracene (DPA) compounds. It was found that singlet exciton diffusion length is improved due to dense network of the sidearms formed in the solid TPA film and this way of tuning exciton diffusion length is very attractive from the perspective of material design for the application in organic optoelectronic devices. It was also found that singlet and triplet exciton diffusion length increases with increasing DPA content in the polymeric DPA films. It was demonstrated that triplet excitons in heavily DPA doped polymeric films are rather mobile and triplet exciton diffusion is not the main limiting factor of the efficiency of light upconversion mediated by triplet-triplet annihilation. Unfortunately, long singlet exciton diffusion length measured in polymeric DPA films causes additional energy losses at nonradiative decay sites. This energy loss can be partly avoided by introducing highly fluorescent singlet sink, which enhances light intensity and improves overall light upconversion efficiency