Effect of patterned substrate on light extraction efficiency of chip-on-board packaging LEDs

We studied the effect of substrate with patterned structure on the light extraction efficiency (LEE) of chip-on-board (CoB) packaging light-emitting diodes (LEDs) by optical simulations based on Monte Carlo ray-tracing method. Two kinds of typical patterned substrates were analyzed which were with conical and spherical structure, respectively. Results show that when the encapsulation layer is without phosphor particles, patterned structures strongly enhance the LEE compared with the flat substrate. The maximum LEE enhancement reaches 41.1% at 1/2 inclination angle α of 30° for the conical structure and 39.5% at 1/2 center angle β of 50° for the spherical structure. However, with the phosphor concentration in the encapsulation layer increasing, the LEE enhancement effect of patterned structures significantly reduces. Even, the enhancement effect almost disappears at the high phosphor concentrations which result in low color correlated temperatures (CCT) of 4000-6000K.