Abstract
Electroluminescence efficiency is crucial for the application of quantum-dot light-emitting diodes (QD-LEDs) in practical devices. We demonstrate that nitrogen-doped carbon nanodot (N-CD) interlayer improves electrical and luminescent properties of QD-LEDs. The N-CDs were prepared by solution-based bottom up synthesis and were inserted as a hole transport layer (HTL) between other multilayer HTL heterojunction and the red-QD layer. The QD-LEDs with N-CD interlayer represented superior electrical rectification and electroluminescent efficiency than those without the N-CD interlayer. The insertion of N-CD layer was found to provoke the Förster resonance energy transfer (FRET) from N-CD to QD layer, as confirmed by time-integrated and -resolved photoluminescence spectroscopy. Moreover, hole-only devices (HODs) with N-CD interlayer presented high hole transport capability, and ultraviolet photoelectron spectroscopy also revealed that the N-CD interlayer reduced the highest hole barrier height. Thus, more balanced carrier injection with sufficient hole carrier transport feasibly lead to the superior electrical and electroluminescent properties of the QD-LEDs with N-CD interlayer. We further studied effect of N-CD interlayer thickness on electrical and luminescent performances for high-brightness QD-LEDs. The ability of the N-CD interlayer to improve both the electrical and luminescent characteristics of the QD-LEDs would be readily exploited as an emerging photoactive material for high-efficiency optoelectronic devices.
Highlights
Graphene is a one-atom-thick graphitic layer with a unique bi-conical zero bandgap electronic structure, and importantly, the bandgap could have been modulated by changing the size, shape and edge states of graphene via quantum confinement and/or edge auxochromic effect[17,18,19]
The QD-LEDs and/or hole-only devices (HODs) with/without N-carbon nanodots (CDs) interlayer were comparatively characterized by electrical measurement and electronic structure analyses
This study investigated the roles of nitrogen-doped CD (N-CD) interlayer inserted between the hole transport layer (HTL) and QD layers for high-efficiency QD-LEDs
Summary
Graphene is a one (or few)-atom-thick graphitic layer with a unique bi-conical zero bandgap electronic structure, and importantly, the bandgap could have been modulated by changing the size, shape and edge states of graphene via quantum confinement and/or edge auxochromic effect[17,18,19]. Due to the ease of the electronic structure and optical property manipulation, the graphene nanostructures (i.e., graphene nanodot, graphene quantum dot, carbon nanodot, etc.) have been exploited as hole (or electron) transport layer or lumophore layer for optoelectronic devices[23,24,25]. The carbon nanodots (CDs), fabricated by bottom-up solution synthesis, have been demonstrated as an emerging photoactive layer with the capacity of ultraviolet (UV)–visible fluorescence[26,27], luminescence up-conversion[28,29], and hot carrier generation[30], all of which are endowed by the aforementioned physical properties. The QD-LEDs and/or hole-only devices (HODs) with/without N-CD interlayer were comparatively characterized by electrical measurement and electronic structure analyses. The synthesis and diverse spectroscopic characteristics of the N-CD layer were demonstrated
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