Open AccessImproving the outcoupling efficiency of indium-tin-oxide-free organic light-emitting diodes via rough internal interfaces
Author(s) -
Boris Riedel,
Inga Kaiser,
Julian Hauss,
Uli Lemmer,
Martina Gerken
Publication year - 2010
Publication title -
optics express
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.394
H-Index - 271
ISSN - 1094-4087
DOI - 10.1364/oe.18.00a631
Subject(s) - materials science , indium tin oxide , oled , electroluminescence , substrate (aquarium) , optoelectronics , indium , layer (electronics) , surface roughness , surface finish , photoresist , quantum efficiency , light emitting diode , optics , diode , photoluminescence , etching (microfabrication) , composite material , oceanography , physics , geology
We present low-cost texturing methods to produce different surface roughnesses on glass substrates. Using sand blasting, abrasion and wet etching we achieve roughnesses of about 50 nm to 250 nm (root mean squared roughness Rq). These textured substrates are used as extraction elements for guided modes and substrate modes in organic light-emitting diodes (OLEDs). We evaporate 50 nm of the high index material Ta₂O₅ on the textured substrate, which acts as waveguide layer, and flatten it with the transparent photoresist SU-8. On top of that, we fabricate indium tin oxide (ITO)-free OLEDs, which are characterized by electroluminescence and photoluminescence measurements. The devices with rough interfaces obtain an up to 37.4% and 15.5% (at 20 mA/cm²) enhanced emission and it is shown that the enhancement is due to an increased outcoupling efficiency.