Probing electronic excitations in organic light-emitting diodes via Raman scattering

摘要

The authors present Raman scattering studies from ethyl-hexyl substituted polyfluorene (PF)-based light-emitting diodes in the presence of injected and photogenerated charge carriers. The Raman background systematically increases with increased charge density and the Raman peaks exhibit asymmetric line shapes characteristic of a Breit-Wigner-Fano (BWF) resonance, indicating interference effects between the electronic continuum and phonons. A complete BWF line shape analysis of the intraring stretch mode at 1605 cm~(-1) is provided. These results are compared with p-doped PF; by increasing the doping concentration, it is seen that the center of the electronic continuum lies at ～0.2 eV.