Thickness-dependent changes in the optical properties of PPV- and PF-based polymer light emitting diodes

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Abstract
We explore the thickness-dependent optical properties of single layer polymer light emitting diodes for two materials, poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylene-ethenylene-2,5-dioctyloxy-1,4-phenylene-ethenylene] (MEH-DOO-PPV) and poly(2,7-(9,9-bis(2-ethylhexyl))fluorene)-2,7-bis(4-methylphenyl)phenylamine (PF with 2% endcap). We compare experimental electroluminescence spectra and radiance values as a function of emissive layer thickness with simulations utilizing dipole methods within a transfer-matrix formalism. The technique is then extended to explore how simulated results depend on the assumed location of emission within the polymer layer. We show that thickness-dependent optical properties of these devices are dominated by interference effects.