Enhancing Luminous Efficiency of Quantum Dot-Based Chip-on-Board Light-Emitting Diodes Using Polystyrene Fiber Mats

Abstract

Even though chip-on-board light-emitting diodes (COB LEDs) with quantum dots (QDs) are attracting much attention for their high optical performance, their luminous efficiency (LE) is still low owing to total internal reflection. To overcome this problem, in this study, a microfiber-silicone hybrid (MFSH) structure is proposed to enhance the LE of QD-based COB LEDs. Polystyrene (PS) fiber films were fabricated by electrospinning and subjected to planar compression modeling to precisely control their film thickness. Subsequently, these films were coated with silicone to finish packaging the COB LEDs. Their diffuse reflectance of the MFSH structures before and after silicone resin encapsulation was analyzed, witnessing a diffuse reflectance at 450 nm of 97.7% when the pure fiber-film thickness increases to $220~\mu \text{m}$ . While applying to COB LEDs, the light output power of devices with MFSH structure increases first and then decreases, causing by the balance of light extraction by the scattering fiber and absorption by the difference between chip height and fiber film thickness. Finally, to increase the light-extraction capacity of COB LEDs, the thickness of the microfiber films was optimized to $25~\mu \text{m}$ at which their LE increased by 29.7% and 31.7% for the blue LED source and QD-based COB LED source, respectively. Therefore, the MFSH structure is an effective packaging method to produce highly efficient COB LEDs.