Improvement of coupling-out efficiency in organic electroluminescent devices by addition of a diffusive layer

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Abstract
We demonstrated that the diffusive layer laminated to glass substrate surface increased the light output of organic electroluminescent devices by extracting and reemitting light trapped in the substrate of such devices. Lamination of the diffusive layer improved the efficiency of the coupling-out factor, which was also changed by the thickness of the electron transporting layer (ETL). High total emitting flux for the sample with ETL thickness around quarter wavelength optical thickness (QWOT) was not improved significantly by lamination of the diffusive layer. Conversely, low total emitting flux for the sample with ETL thickness around 2QWOT without the diffusive layer was largely increased by the lamination of the diffusive layer, which was due to the extraction of waveguided light from the substrate mode. As the results, large dependence of total emitting flux on ETL thickness was significantly minimized by the lamination of diffusive layer. In addition, lamination of the diffusive layer also significantly reduced the variation of emission color and luminous intensity, which were strongly dependent on viewing angle and ETL thickness for the sample without the diffusive layer.