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Fast and cost effective fabrication of microlens arrays for enhancing light out-coupling of organic light-emitting diodes

: Stellmacher, Andre; Liu, Yuan; Soldera, Marcos; Rank, Andreas; Reineke, Sebastian; Lasagni, Andrés-Fabián


Materials letters 252 (2019), pp.268-271
ISSN: 0167-577X
Journal Article
Fraunhofer IWS ()
organic light-emitting diode; light out-coupling; direct laser interference patterning; nano-imprint lithography; laser processing; polymer

The efficiency of organic light-emitting diodes (OLEDs) deposited on flat substrates is strongly limited by the total internal reflection at the air-substrate interface. An effective strategy to reduce the amount of substrate modes and enhance the light out-coupling into the air is attaching a microlens array (MLA) on the external surface of OLEDs. In this study, polymeric MLA with periods between 1.2 µm and 2.0 µm are patterned by plate-to-plate nano-imprint lithography using metallic stamps structured by direct laser interference patterning. When MLA with a spatial period of 2.0 µm and a structure depth of 200 nm are employed on red, green and blue OLEDs, the external quantum efficiency is increased to 11.4%, 6.6% and 12.7%, respectively, due to a reduction of internally reflected radiation at the air-MLA-glass interfaces.