Facile fabrication of microlens array on encapsulation layer for enhancing angular color uniformity of color-mixed light-emitting diodes

• DOI: 10.1016/j.optlastec.2021.107227
• Publication Date: 2021-05-21T09:19:24Z
• Authors: Luyao Mei; Chao Qu; Zengyi Xu; Guangxu Wang; Jianli Zhang; Xing Guo; Yang Peng
• Keywords: 02 engineering and technology; 0210 nano-technology

Abstract In this work, we proposed a concave microlens array (MLA) on an encapsulation layer to enhance the angular color uniformity (ACU) of color-mixed light-emitting diodes (cm-LEDs). The MLAs with continuously adjustable curvature were fabricated by using a low-cost and facile approach based on water droplets condensation. Through initiative cooling, the water vapor was condensed on the surface of a polymer film and then the water droplets array was utilized as a template to obtain the MLA. By controlling the cooling temperature at −15, 0, and 15 °C, the sag height-to-diameter ratios (aspect ratio, AR) of MLAs were obtained at 0.68, 0.63, and 0.53, respectively. Through adjusting the three-phase state of the polymer-water droplets-sacrificial layer system by introducing a second-step cooling temperature of 0 and −15 °C after the first-step cooling temperature of 15 °C, the ARs were further decreased to 0.49, and 0.37, respectively. Haze tests demonstrated the scattering ability of MLAs, and encapsulation layer with MLA was applied in packaging of the cm-LEDs to enhance their ACU and luminous efficacy (LE). Consequently, the maximum correlated color temperature (CCT) deviation of the cm-LEDs was reduced from 853 K to 273 K and the LE of cm-LEDs was increased by 9.1% at 200 mA after applying the fabricated MLAs.