Light extraction from quantum dot light emitting diodes by multiscale nanostructures
Improving the light extraction efficiency by introducing optical–functional structures outside of quantum dot light emitting diodes (QLED) for further enhancing the external quantum efficiency (EQE) is essential for its application in display and lighting industrialization. Although the efficiency of QLED has been optimized by controlling of the synthesis of the quantum dots, the low outcoupling efficiency is indeed unresolved because of total internal reflections, waveguides and metal surface absorptions within the device. Here, we are utilizing multiscale nanostructures attaching to the outer surface of the glass substrate to extract the trapped light from the emitting layers of QLED. The result indicates that both the EQE and luminance are improved from 12.29% to 17.94% and 122400 cd m-2 to 178700 cd m-2, respectively. The maximum EQE and current efficiency improve to 21.3% and 88.3 cd A−1, respectively, which are the best performance among reported green QLED with light outcoupling nanostructures. The improved performance is ascribed to eliminate total internal reflection by multiscale nanostructures attached to the outer surface of the QLED. Additionally, the simulation result of Finite-difference time domain (FDTD) also demonstrates the light trapping effect is reduced by the multiscale nanostructures. The design of the novel light outcoupling nanostructure for further improving the efficiency of QLED can promote its application in display and lighting industrializations.