Optimization of opto-electronic property and device efficiency of polyfluorenes by tuning structure and morphology

Polyfluorene-based oligomers and polymers (PFs) have been studied intensively as active materials for organic optoelectronic devices. In this review, the optimization of the opto-electronic property and device efficiency of polyfluorenes in the field of light-emitting diodes (LEDs) and photovoltaic cells (PVs) by tuning structure and morphology are summarized in terms of two typical modification techniques: copolymerization and blending. The relationships between molecular structures, thin film morphologies, opto-electronic properties and device efficiencies are discussed, and some recent progress in LEDs and PVs is simultaneously reviewed. After the introduction, the basic knowledge of molecular structures and properties of polyfluorene homopolymers is presented as a background for a better understanding of their great potential for opto-electronic applications. Immediately after this, three different opinions on the origin of low-energy emission band at 520-540nm in polyfluorene-based LEDs are addressed. Rod-coil block copolymers and alternative copolymers are focused on in the next section, which are a vivid embodiment of controlling supramolecular structures and tailoring molecular structures, respectively. In particular, various supramolecular architectures induced by altering coil blocks are carefully discussed. Recent work that shows great improvement in opto-electronic properties or device performance by blending or doping is also addressed. Additionally, the progress of understanding concerning the mechanisms of exciton dynamics is briefly referred to.