Tunneling effect in quantum-dot light-emitting diodes

Charge carrier transportation in semiconductor films is a fundamental but crucial process for the light-emitting diodes. Although there have been many studies on charge transport properties of devices based on traditional inorganic crystals and organic amorphous films, such charge behavior within emerging quantum-dot light-emitting diodes (QLEDs)—which are composed of amorphous nanocrystal films with strong quantum confinement effects—has rarely been discussed. Here, we demonstrate that the tunneling effect really occurs in the hybrid QLEDs with ZnO as the electron-transport layer. By suppressing the thermal effect, a negative differential resistance (NDR) phenomenon is observed by decreasing the working temperature of the QLED low to 150 K. Two types of quantum dots (QDs) with different shell structures (i.e., different tunneling barrier) are used to comparatively examine the tunneling effect. The current density–voltage properties of the QLEDs reveal that the device based on QDs with the sharp core-shell structure (i.e., larger tunneling barrier) exhibits more obvious NDR behavior, which is attributed to the stronger tunneling effect. Our results offer significant insight into the charge dynamics and working mechanism in the QLEDs.