Effect of microlens arrays on light extraction efficiency in red and green quantum-dot light-emitting diodes

The efficiency of quantum-dot light-emitting diodes (QLEDs) was improved by utilizing a microlens array (MLA) film, and the effect of the MLA film was investigated through optical simulation. The MLA films enhanced luminance by 1.51 and 1.28 times at 5 V for green and red QLEDs, respectively. The green and red QLEDs exhibited high external quantum efficiencies of 14.69 % and 19.87 %, and efficiency enhancement ratios were approximately 56.97 % and 21.68 %, respectively. Furthermore, the electroluminescence spectra remained stable, ensuring color consistency. By altering the dipole orientation of the emitter in the optical simulation, we observed that as the dipole became more vertical, the efficiency improved due to increased light extraction by the MLA. In addition, varying the number of microlens array by changing the microlens radius in the same emission area resulted in a consistent enhancement ratio, while increasing the MLA density significantly improved light extraction. These results suggest that MLA films effectively enhance the efficiency of QLEDs with color stability, providing a strategy for improving their performance.