Determination of exciton diffusion coefficient in conjugated polymer films: Novel method based on spectroelectrochemical techniques

The understanding of exciton dynamics is a central issue in the operation of conjugated polymer-based optoelectronic devices, like solar cells, light-emitting diodes or electrochemiluminescent cells. In this work, we explore the applicability of combined in situ electrochemical fluorescence and UV-vis spectroscopies for the study of electrochemically induced quenching of photoluminescence as novel tools for the determination of exciton diffusion in a model conjugated polymer, poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylvynilene] (MEH-PPV). It is demonstrated that the quenching process observed upon electrochemical doping follows a linear Stern-Volmer mechanism at low doping levels, with a time-independent rate constant typical of diffusion-controlled annihilation processes. From the Stern-Volmer rate constant and the exciton-polaron critical distance, an exciton diffusion coefficient is derived whose value is in close agreement with those reported in the literature. These results support the suitability of these spectroelectrochemical techniques as fast and powerful alternative tools for the reliable determination of exciton diffusion coefficients in conjugated polymers.