| Summary: | 碩士 === 南臺科技大學 === 光電工程系 === 103 === Indium tin oxide (ITO) films with micro-structured surfaces and on top coated nickel oxide (NiOx) interlayer were fabricated to serve as an anode for OLED applications. The surface micro-structures include recessed and aluminum zinc oxide (AZO) embedded structures. Both structures had 100, 150 and 200 nm recessed and embedded depths and with a coverage ratio of 7.9%, 14.1%, 20.9%, and 27.7% AZO. On top of these structures a layer of 5-nm-thick NiOx was formed. The influences of physical dimensions of these structures and the coated NiOx interlayer on the optical, electrical and topographical properties of ITO films were examined. OLED devices were fabricated on these structures and were investigated to realize how these micro-structures influence the characteristics of OLEDs, especially on the light extraction efficiency.
Result showed that an OLED device with an ITO anode of 150 nm and 27.7% recessed could reach a current efficiency of 66.6% cd/A, enhanced by 33% compared to a planar device of 50.3% cd/A. Whereas﹐an OLED device with an AZO embedded ITO anode having embedded depth of 50 nm and a coverage ratio of 20.9% performed a current efficiency of 59.9 ca/A, enhanced by 35% compared to the planar device of 44.3 cd/A. When a layer of NiOx was introduced, current efficiency could be further enhanced by 46% and 42% for the recessed and AZO embedded devices, respectively. The enhanced efficiency was mainly attributed to the created micro-structures that generate deflection and scattering interfaces to re-guide the emitted light away from being total reflected, leading to an enhanced light extraction efficiency. The inserted high work function NiOx further reduces the potential barrier at the ITO/organic interface, allowing more holes to be injected into the device for higher internal quantum efficiency. And as a result, due to the negligible influence on ITO properties with the introduced NiOx interlayer, the external efficiency of OLEDs could be further improved.
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