Molding hemispherical microlens arrays on flexible substrates for highly efficient inverted quantum dot light emitting diodes

Highly efficient flexible red quantum-dot light-emitting diodes (QLEDs) are successfully fabricated by molding hexagonally close-packed hemispherical microlens arrays (MLAs) on the front side of poly(ethylene-terephthalate) (PET) substrates. Compared with the conventional device, the external quantum efficiency (EQE) of the MLA-containing QLED is increased by a factor of 64%, from 8.6% to 14.1%. And a record-maximum luminous efficiency of 24.8 lm W-1 is achieved at an applied voltage of 3.0 V after introducing the MLAs into the device. The emission distribution of the device is largely changed due to the introduction of MLAs, displaying an anisotropic and non-Lambertian profile, i.e., higher emission intensity at high viewing-angle directions in its emission pattern than the Lambertian distribution. However, the EL spectra and the color coordinates of the QLEDs are hardly affected by the introduction of microstructured MLAs.