Research On Gradient Refractive Index Structure For High Power LED Packaging

Light emitting diode(LED) has been widely used because of its energy saving, environmentally friendly, long life and high brightness. Solid-state lighting device based on high power white LED is considered to be the fourth generation lighting source. However, there are still some problems to be solved for high power LED packaging and improving the light extraction efficiency(LEE) of LED has been a hot topic. In this paper, gradient refractive index(GRIN) structure is proposed to reduce the energy loss caused by total reflection and Fresnel reflection, so as to improve the LEE of LED.In this paper, the mechanism of high power LED and the factors affecting the LEE are analyzed, GRIN structure for single-chip LED and GRIN structure with plane shape package and lens for multi-chip LED are proposed. Optical models are established and simulation respectively discusses the LEE of GRIN structure with plane shape package and lens compared with LED packaged in traditional methods. Simulation results showed that GRIN structure with plane shape package(RI are 1.54 and 1.41 respectively) has a little higher LEE, which only increased by 0.41% than that of LED packaged with only one kind of encapsulant(RI is 1.54). The GRIN structure with lens has the most obvious improvement, whose LEE is 30.52% higher than that of GRIN structure with plane shape package. At the experimental stage, several samples were prepared and tested to verify the performance of GRIN structure. The LEE increment of GRIN structure with plane shape package is still not obvious, but the LEE of GRIN structure with lens is improved by 6.85%.This paper also further explore the optimization method of GRIN structure, the RI of each encapsulant layer of single chip high-power LED and the lens shape of the GRIN structure of the multi-chip LED is optimized based on the analysis of light extraction process of GRIN structure, and their light extraction performance is simulated and analyzed.