On the Electroluminescence Turn‐On Mechanism of Blue Quantum‐Dot Light‐Emitting Diodes

Abstract

Abstract A clear understanding on the fundamental working mechanisms of quantum‐dot light emitting diodes (QLEDs), especially the blue devices, is always sought after. Here the electroluminescence (EL) turn‐on mechanism of blue QLEDs is unraveled by structure engineering of the hole‐transport layers (HTLs). It is demonstrated that the EL turn‐on in blue QLEDs is highly dependent on the charge‐transport polarity of the HTLs. Energy transfer between HTLs and the blue quantum dots (QDs) occurs for the QLEDs based on bipolar HTLs, and, in contrast, charge injection is responsible for EL turn‐on of the blue devices consisting of unipolar HTLs. In addition, large hole‐injection barrier results in serious accumulation of holes at the interface of HTLs/QDs, then inducing serious electrons leakage into the HTLs, thereby leading to poor device efficiency under low driving current. It is suggested here that confining the carriers to the quantum dots and reducing the hole‐injection barrier remain two critical aspects to optimize the performance of blue QLEDs.