Measuring the light emission profile in organic light-emitting diodes with nanometre spatial resolution

Determining the precise shape of the emission profile across the thickness of the active layer in organic light-emitting diodes is of importance for device optimization and assessing the validity of advanced device models. We present a comprehensive method for accurately measuring the shape of the emission profile, the intrinsic spectrum of emitting dipoles and the emitting dipole orientation. The method uses a microcavity light outcoupling model, which includes self-absorption and optical anisotropy, and is based on the full wavelength, angle and polarization resolved emission intensity. Application to blue (polyfluorene-based) and orange-red (NRS-PPV) polymer organic light-emitting diodes reveals a peaked shape of the emission profile. A significant voltage and layer thickness dependence of the peak positions is observed, with a demonstrated resolution better than 5 nm.