Optical Performance Enhancement for Chip-on-Board Packaging LEDs by Adding TiO2/Silicone Encapsulation Layer

Owing to the strong light scattering effect of TiO2 nanoparticle and silicone composite, a method for improving optical performances of chip-on-board (COB) packaging LEDs was proposed through introducing a thin auxiliary encapsulation layer with high-concentration TiO2 nanoparticle and silicone composite below the main encapsulation layer. Its optical performance enhancement effect was examined by experiments. Results show that for the main encapsulation layer only consisting silicone, the proposed packaging method enhances the light extraction efficiency (LEE) up to 65%. However, for another case in which the main encapsulation layer is phosphor and silicone composite, the LEE enhancement effect is correlated to the phosphor concentration. When the phosphor concentration reduces from 0.12 to 0.035 g/cm3, the LEE enhancement effect increases from 6% to 24%. Meanwhile, the angular correlated color temperature (CCT) deviation is reduced from 900 to 470K between viewing angles from -90° to 90°, when the average CCT is ~5500K.