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22 September 2015 Dependence of light outcoupling in organic light-emitting devices on ITO thickness and roughness
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The efficiency of organic light-emitting devices (OLEDs) is shown to significantly depend on both the thickness and roughness of the indium tin oxide (ITO) anode. The effects of changing the ITO thickness from 45 nm to 130 nm are found to be able to vary the current efficiency by 40%. The underlying mechanism is studied and revealed to be related to microcavity effects. The transmittance of the ITO substrate changes significantly with the ITO thickness, resulting in variations in microcavity, and thus light outcoupling efficiency. On the other hand, the effects of increasing the ITO roughness (rms) from 3.3 nm to 8.5 nm are found to increase light scattering at the ITO/organic interface, thus improving extraction of light trapped in the organic/ITO wave-guided mode. In addition to the enhancement in current efficiency, the device fabricated on rough ITO shows similar driving voltage to that made on smooth ITO, indicating that charge balance is not altered by ITO roughness. Contrary to common belief in the community, the lifetime of the OLED is not affected when using rough ITO. The results demonstrate the significant efficiency benefits of using ITO with optimal thicknesses and higher roughness in OLEDs.
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Yingjie Zhang and Hany Aziz "Dependence of light outcoupling in organic light-emitting devices on ITO thickness and roughness", Proc. SPIE 9566, Organic Light Emitting Materials and Devices XIX, 95661R (22 September 2015);

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