Abstract
A simple and efficient method for transforming conformation of parts of chains in the amorphous phase in a conjugated polymer to extended conjugation length (termed as β phase) is disclosed. The β phase acts as a dopant and can be termed self-dopant. The generated self-dopant in the amorphous host allows an efficient energy transfer and charge trapping to occur and leads to more balanced charge fluxes and more efficient charge recombination. For example, a polyfluorene film was dipped into a mixed solvent/non-solvent, tetrahydrofuran/methanol in volume ratio of 1:1, to generate a β-phase content up to 1.32%. A polymer light emitting diode with the dipped polyfluorene film as a light emitting layer therein provides a more pure and stable blue-emission (solely from the self-dopant) with CIE color coordinates x+y<0.3 and a performance of 3.85 cd A−1 (external quantum efficiency 3.33%) and 34326 cd m−2.