Simone Hofmann

Outcoupling efficiency in small-molecule OLEDs:from theory to experiment

The extraction of the luminous power internally generated by organic light emitting diodes (OLEDs) is still the most severe limitation in the overall efficiency of these devices. We present a joint theoretical and experimental study aimed to quantitatively evaluate the light outcoupling limitations of planar p-i-n type small-molecule OLEDs, both in bottom and top emitting configuration. We discuss the physical origin of these limitations by analyzing internal optical losses and overall light conversion efficiency in OLEDs.

Quantitative allocation of Bragg scattering effects in highly efficient OLEDs fabricated on periodically corrugated substrates.

Bragg scattering effects in bottom-emitting organic light-emitting diodes (OLEDs) grown on corrugated aluminum-doped zinc oxide electrodes are analyzed. Periodic corrugation is introduced by structuring the oxide electrode via UV laser ablation, a process that enables flexible adjustment of the period and height of corrugation. We demonstrate that fabrication of stable and electrically efficient OLEDs on these rough substrates is feasible. Sharp spectral features are superimposed onto the broad emission spectra of the OLEDs, providing clear evidence for Bragg scattering of light from guided modes into the air cone. Theoretical analysis based on an emissive dipole model and conservation of momentum considerations allows a quantitative description of scattering and the associated dispersion relations.