Light extraction employing optical tunneling in blue InP quantum dot light-emitting diodes

Blue InP quantum dot light-emitting diodes (QLEDs) are promising candidates for environmental-friendly displays. To achieve efficient blue InP QLEDs through light extraction, the internal grating structure is a feasible way to extract waveguide modes, but it may bring complicated fabrication process and deteriorated electrical performance. In this work, we proposed an effective strategy to extract light from waveguide modes to air modes by using a thin hole transport layer (HTL), a high-index substrate, and substrate surface-roughening. Through optical tunneling, the thin HTL and the high-index substrate facilitate light transmission from waveguide modes to substrate modes. Thus, substrate surface-roughening can be applied to further extract light from enhanced substrate modes to air modes. As a result, light extraction efficiency has been significantly improved, leading to an external quantum efficiency enhancement from 2.1% to 2.8%, which is a record value among counterparts to date. This light extraction strategy is simple but effective to exploit the potential of high-efficiency (blue InP) QLEDs.