(a) Outcoupling efficiency vs ratio of microlens to OLED diameter as calculated via 3D Monte Carlo simulations for hexagonal microlens arrays. Parameters used were refractive indices of the microlens and glass substrate of 1.45, and the corresponding microlens contact angle of the microlens shown in Fig. 2(a), inset, is . The open circles and dashed line indicate that ray optics may not be suitable when the microlens diameter approaches the light wavelength. Inset: Schematic of the OLED structure with the microlens arrays incorporated on the substrate; (b) outcoupling efficiency vs microlens diameter for an OLED with a diameter, as calculated via wave optics finite difference time domain method, assuming emitting light wavelength is . Note that the calculation differs from the ray optics solution in (a) as the microlens diameter approaches the light wavelength.
(a) Outcoupling efficiency calculated as a function of microlens index of refraction (solid squares), assuming a microlens shape; and as a function of the microlens shape (open squares) from flat to a full hemisphere , assuming indices for the microlens and glass substrate are equal . Inset: Definition of the contact angle of the cone with the substrate . (b) Simulated light flux on the outcoupling surface vs the distance from the OLED center as a function of glass substrate thickness, assuming an OLED radius of .
Schematic of the mold preparation and imprint lithography process: hexagonal arrays of small openings are patterned on photoresist on a glass substrate (1). The substrate is wet etched in buffered oxide etch to achieve an approximately hemispherical shape (2). After the removal of the photoresist and the mold treatment, the mold is pressed against a thermal plastic PMMA layer on a second glass substrate at (3) and released after cool down (4).
(a) Scanning electron micrograph of the glass mold after wet etching and (b) of the imprinted microlens array.
(a) External quantum (solid) and power (open) efficiencies in the forward viewing space of WOLEDs on glass substrates with (squares) and without (circles) microlenses. (b) The enhancement of luminance of WOLEDs by using microlens arrays compared to a flat glass substrate as a function of current density. Inset: Luminance vs current density characteristics for WOLEDs with microlenses.
(a) Enhancement of power efficiency of WOLEDs using microlens arrays compared to a flat glass substrate as a function of luminance. (b) Normalized electroluminescence spectra at a current density of as a function of viewing angle with respect to the substrate normal. Inset: Normalized light intensity vs viewing angle for WOLEDs on glass substrates with (solid line) and without (dashed line) microlenses; a Lambertian intensity output pattern (open circles) is also plotted for reference.
(a) Outcoupled light flux vs viewing angle for both WOLEDs in Fig. 5 (b) Outcoupled light flux vs viewing angle for devices with and without microlens arrays as calculated via 3D Monte Carlo simulations.
Article metrics loading...
Full text loading...