Field-induced luminescence quenching in electroluminescent conjugated polymers

The basic physical processes of field-induced luminescence quenching in electroluminescent conjugated polymers is studied by a theoretical model of electron-lattice tight binding with an applied electric field, plus the extended Hubbard interactions, in an unrestricted Hartree-Fock approximation. It is found that there exists a critical field E_c, beyond which the self-trapping singlet-and triplet-excitons (the emitting species) in conjugated polymers will be split directly into hole-polarons and electron-polarons, leading to luminescence quenching. Why the luminescence intensity decreases with increase of the applied field and why the luminescence intensity will not be quenched completely in stronger fields are elucidated. The critical field increases with the electron interactions and the binding energy of self-trapping excitons. Possible approaches to decrease field-induced luminescence quenching are increasing the binding energy of the exciton and reducing the conjugation length.