Enhancing efficiency of blue thermally activated delayed fluorescence organic light-emitting device using a high refractive index material-based light extraction layer

초록

A high-refractive-index periodic hole structure based on silicon nitride (Si3N4) was incorporated into thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs) to improve optical efficiency. Due to its high refractive index, Si3N4 serves as an effective optical scattering medium, enhancing light extraction in OLEDs. The high-refractive-index structure (HRS) was achieved through laser interference lithography (LIL), which defined a periodic pattern in a photo-resist (PR) layer. This patterned PR layer subsequently functioned as an etch mask, allowing direct replication of the nanostructures onto the underlying Si3N4 layer. Compared to conventional patterning methods, LIL provides higher precision and faster processing, making it a cost-effective solution for large-area nanoscale fabrication with accurate structural control. Key parameters affecting the LIL, development, and reactive-ion etching (RIE) processes were systematically investigated. These included the half-angle between interfering beams, exposure dosage, volume ratio of PR-tothinner, development time, volume ratio of developer with deionized water, and etching duration-all of which impact the final structure. To enhance light extraction efficiency at a wavelength of 480 nm, a finite-difference time-domain (FDTD) simulation was utilized to fine-tune the HRS dimensions. The resulting optimized HRS significantly enhanced device performance, increasing the external quantum efficiency (EQE) by 14.58 %, current efficiency by 37.48 %, and power efficiency by 38.37 %.

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