Organic light-emitting diodes with photonic crystals on glass substrate fabricated by nanoimprint lithography

Abstract

The authors have fabricated organic light-emitting diodes (OLEDs) having two-dimensional photonic crystals (PC) as light extraction elements by employing nanoimprint lithography technique. PCs were imprinted on the glass substrate and OLED layers were formed on the imprinted side of the glass substrate. The device having PC showed the improvement of luminance by a factor of 1.5 compared to normal devices. The authors conclude that the nanoimprint lithography is very useful for the fabrication of the OLEDs with PC.

Highly efficient inverted polymer light-emitting diodes using surface modifications of ZnO layer

“…One method of enhancing the out-coupling efficiency is to use a high-refractiveindex glass substrate and a hemisphere microlens thereon [16][17][18] . Moreover, a Bragg diffraction grating (BDG), a low-index grid and an internal scattering structure of the organic layer have been introduced in these devices for the light extraction of the indium tin oxide (ITO)/organic WG mode [19][20][21][22][23][24] . However, BDGs fabricated using the electron-beam lithography 19 , nanoimprinting 20 and holographic methods [21][22][23] incur the high costs and require complex techniques.…”

“…Moreover, a Bragg diffraction grating (BDG), a low-index grid and an internal scattering structure of the organic layer have been introduced in these devices for the light extraction of the indium tin oxide (ITO)/organic WG mode [19][20][21][22][23][24] . However, BDGs fabricated using the electron-beam lithography 19 , nanoimprinting 20 and holographic methods [21][22][23] incur the high costs and require complex techniques. In addition, it is difficult to extract at broad range of light emission using BDGs with regular periodic structures for white OLEDs because such a BDG extracts specific emission wavelengths in accordance with Bragg's law, depending on the specific grating period and angle.…”

Effects of Metallic Absorption and the Corrugated Layer on the Optical Extraction Efficiency of Organic Light-Emitting Diodes

“…It means that the corrugation can be a useful method to increase the optical extraction of OLEDs, only if the cathode doesn't absorb the light. This metallic absorption may explain the limited success of the structure, which has an emission layer coated over the photonic crystal patterned substrate 3 . Therefore, the corrugation of the emission layers requires careful consideration with respect to the metallic absorption and the risk of short-circuit, as well as a scalable fabrication technique for more practical applications.…”

“…For a typical OLED structure, the extraction efficiency is only ~20 % 1,2 . Various efforts have been made to improve the optical extraction [3][4][5] . Most approaches deal with patterns inside or on the surface of the device in order to reduce internal reflections.…”

Bilayer hybrid nanoimprinting method for fabricating embedded silver nanostructure arrays with enhanced photoluminescence

“…[19][20][21][22] However, these efficiency improvements are achieved at the cost of increased leakage currents because conformally deposited electrodes and emitters are characterized by elongated current paths and degraded uniformity. For example, nanopatterned organic light-emitting diodes (OLEDs) with a photonic crystal structure exhibit even lower luminous efficiencies at current densities larger than 5 mA∕cm 2 ; however, the efficiencies can be increased by 13% by planarization of the device with multiple spin-coated layers of ZnO sol-gel.…”