Blue chip type white LED to improve light efficiency
a) Improve the internal quantum efficiency to generate more blue light in the active region and reduce the absorption of blue light output. With the development of epitaxial growth technology and multi-quantum well structure, the internal quantum efficiency of ultra-high brightness LED has been greatly improved, and blue LED has reached more than 90%.
b) To improve the efficiency of light extraction, flip structure is adopted to avoid the electrode and gold wire of the formal structure to block the light. Balance the contradiction between light absorption and diffusion current of transparent conductive film. The bottom reflector reflects the blue light towards the front light. Surface mapping or surface roughening techniques can avoid excessive total reflection of luminescence caused by large refractive index difference. Packaging material close to the chip refractive index.
c) Improve the external quantum efficiency of phosphor photoluminescence conversion to develop phosphor materials and ratios with high photoluminescence conversion efficiency.
d) Improve the optical emission efficiency of the package. The high refractive index of the package material is conducive to the extraction rate of the chip's light output, but it also increases the difference between the refractive index and the air. For the planar package, the inward total reflection between the interface and the air increases, and the light efficiency decreases. Therefore, a secondary transparent package layer with refractive index transition can be added to the planar package. In addition, for non-planar packages, the thickness and shape of the phosphor coating and the shape of the package structure are improved to avoid excessive total reflection of the emitted light caused by large refractive index differences.