Quantum-Rod On-Chip LEDs for Display Backlights with Efficacy of 149 lm W-1 : A Step toward 200 lm W-1.

Efficient white light-emitting diodes (LEDs) with an efficacy of 200 lm W-1 are much desirable for lighting and displays. The phosphor-based LEDs in use today for display applications offer poor color saturation. Intensive efforts have been made to replace the phosphor with quantum-dot-based downconverters, but the efficiency and stability of these devices are still in their infancy. Quantum rods (QRs), nanoparticles with an elongated shape, show superior properties such as relatively larger Stokes shifts, polarized emission, and high light out-coupling efficiency in the solid-state. However, these QRs usually suffer from poor optical quality for PL wavelengths < 550 nm. Herein, a gradient alloyed CdSe/Znx Cd1- x S/ZnS and CdSe/CdS/ZnS core/shell/shell QR downconverters showing high efficacy LEDs covering a wide color gamut are reported. These QRs show high stability and a precisely tunable photoluminescence peak. The engineered shell thickness suppresses energy transfer and thus maintains the high quantum yield in the solid-state (81%). These QR-based LEDs attain an efficacy of 149 lm W-1 (@10mA) and wide color gamut (118% NTSC), which is exceedingly higher than state-of-the-art quantum dots and phosphor-based on-chip LEDs.