Micro-lens-like structures fabricated on indium tin oxide were employed to promote light extraction efficiency of an organic light-emitting diode (OLED). Four array patterns with coverage ratios of 7.9%, 14.1%, 20.9% and 27.7% were examined. The current efficiency of OLED was enhanced by 26.5% for the 14.1% recessed device (4.8cd/A) compared with the planar device (3.8cd/A). The improved current efficiency was attributed to the additional light-emitting area generated on the recess wall as well as the light scattering/deflection effects on the recessed surfaces. The current efficiency was found coverage-ratio independent suggesting that the light extraction is limited by the arrangement of the recesses.
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