Field Induced Singlet Exciton Dissociation and Exciton-Exciton Annihilation in MEH-PPV Films Studied by Photocurrent Spectra

Abstract

In this paper we investigate different processes which lead to charge carrier generation in ITO/PEDOT:PSS/MEH-PPV/Al photodetector.Primary photogenerated singlet excitons contribute the photocurrent directly through dissociation on the electrodes. Singlet exciton distribution in the active area of the photodetector is calculated on the base of continuity equation including exciton generation, diffusion, and recombination. Depending on the applied electric field and incident photon flux secondary charge carrier generation processes appear in the active MEH-PPV film. Two bulk charge generation mechanisms are considered. Nonlinear recombination of excitons through exciton-exciton annihilation leads to electron and hole polaron generation. Exciton states are also depopulated by exciton dissociation in the presence of high electric field. We assume hole polarons to be majority charge carriers. Polaron contribution to photocurrent is calculated by solving the continuity and drift-diffusion equations for these carriers. Photocurrent spectra are measured for different bias voltages and different incident photon flux intensities. A good agreement between experimental and simulated data confirms our theoretical approach.