Surface wrinkle formation by liquid crystalline polymers for significant light extraction enhancement on quantum dot light-emitting diodes

Abstract

We propose an optimal outcoupling structure of a quantum-dot light-emitting diode (QLED) and present material properties based on numerical calculations via the ray-tracing method, in which light extraction properties are obtained according to the surface wrinkles on a substrate. After analyzing the designed microstructure elements, the optimal model was derived and applied to the QLEDs; consequently, the outcoupling efficiency enhanced by 31%. The liquid crystalline polymer forming the random surface wrinkles not only achieves an excellent light extraction through plasma crosslinking but also facilitates large-area processes. We propose an optical design rule for high-efficiency QLED design by analyzing the electro-optical efficiency, emission spectrum, and angular radiation pattern of the optical device.

Enhanced emission directivity from asymmetrically strained colloidal quantum dots

“…2A). The second derivative of absorbance spectra reveals that the broadening in the first exciton peak is due to the splitting of exciton states, which, according to previous and our own theoretical simulations, are related to light and heavy holes (37,42), and a similar phenomenon has been observed in dot-in-plate nanocrystals (19). The splitting reaches 45.2 meV in our final CQD, which is much bigger than the thermal activation energy (~26 meV) at room temperature, and therefore, the thermal population of higher energy state can be suppressed.…”

“…Microcavities, microlenses/arrays, and surface roughening have been used to improve light extraction (16)(17)(18)(19)(20); however, viewing angle becomes compromised, and the fabrication process is significantly more complicated in these approaches (15,21,22). In contrast, orienting the emission dipole moment of the CQDs to converge the photon emission angle is a more feasible strategy to extract light.…”

Polymer Dispersed Liquid Crystal Imprinted by Microlens Array for Enhanced Outcoupling Efficiency of Organic Light Emitting Diode

“…Light extraction technologies primarily focus on minimizing light loss by reducing the refractive index mismatch within the OLED, thereby lessening total internal reflection [ 10 , 11 ]. Various optical structures have been integrated into OLED devices for this purpose, including microlens array (MLA) [ 12 , 13 ], visible parylene film [ 14 ], MLA patterned parylene substrate [ 15 ], random surfaces [ 16 ], porous cellulose paper [ 17 ], and light scattering layers [ 18 , 19 , 20 ]. Among these studies, research using parylene has produced a light extraction film that can serve as a flexible substrate and exhibits a high outcoupling efficiency exceeding 20%.…”