Finite difference time domain analysis of the light extraction efficiency in organic light-emitting field-effect transistors

The authors report on three-dimensional numerical optical simulations of the emission outcoupling efficiency in light-emitting devices with a field-effect carrier transport. The finite difference time domain method is applied to organic thin film structures on a silicon substrate with metal and metal oxide electrodes. Simulations are performed for Au, Ag, and indium tin oxide electrodes in a bottom gate, bottom contact geometry. Additional attention is paid to the dependence on electrode thickness and contact shape. We demonstrate that in unipolar driven devices with Si gate, silicon dioxide insulator, and 40 nm thick organic films, the maximum outcoupling efficiency is below 10%. This value can be increased by the implementation of a metal reflecting layer on the Si substrate. In further studies, the emission efficiency in the ambipolar regime is investigated. The result presents the dependence of light extraction on the light source-electrode distance for rectangular and wedge shaped contacts. (C) 2008 American Institute of Physics.