Theory of photoinduced charge transfer in a molecularly doped conjugated polymer

Abstract

In a molecularly doped conjugated polymer, it is possible for an exciton, photoexcited on the polymer, to decay into a free charge in the polymer's valence or conduction band and a charge of opposite sign in an available level on an adjacent dopant molecule. Such pair processes, which conserve energy, can occur if the energy ${\mathrm{\ensuremath{\omega}}}_{0}$ of the polymer exciton lies within the continuum part of the charge-transfer electron-hole excitation spectrum of the polymer/molecule composite. We calculate the corresponding exciton decay rate 1/\ensuremath{\tau}(\ensuremath{\Delta}) for two types of matrix element that describe the microscopic charge-transfer event. This rate is a maximum when the energy \ensuremath{\Delta} of the molecular acceptor level lies below the conduction-band edge by an amount that is a little more than the exciton's binding energy, a similar result occurring for the case of hole transfer to the molecule. The reduction of 1/\ensuremath{\tau} by the Coulomb interaction between the electron and hole in the final state is important. \textcopyright{} 1996 The American Physical Society.