Carrier recombination spatial transfer by reduced potential barrier causes blue/red switchable luminescence in C8 carbon quantum dots/organic hybrid light-emitting devices

Abstract

The underlying mechanism behind the blue/red color-switchable luminescence in the C8 carbon quantum dots (CQDs)/organic hybrid light-emitting devices (LEDs) is investigated. The study shows that the increasing bias alters the energy-level spatial distribution and reduces the carrier potential barrier at the CQDs/organic layer interface, resulting in transition of the carrier transport mechanism from quantum tunneling to direct injection. This causes spatial shift of carrier recombination from the organic layer to the CQDs layer with resultant transition of electroluminescence from blue to red. By contrast, the pure CQDs-based LED exhibits green–red electroluminescence stemming from recombination of injected carriers in the CQDs.

Quasi‐White Light‐Emitting Devices Based on SiC Quantum Dots

“…It also suggests that the presence of the TPBI layer helps to stabilize the device structure and improve its performance. There are potential barriers for carriers at the SiC QD–ITO interface and the SiC QD–Al interface, as shown by the schematic diagram in Figure , therefore, at low bias the carrier transport is dominated by direct quantum tunneling . Note that in Figure , the ITO anode and the Al cathode have work functions of 4.7 and 4.3 eV (below the vacuum energy level), respectively .…”

“…There are potential barriers for carriers at the SiC QD-ITO interface and the SiC QD-Al interface, as shown by the schematic diagram in Figure 4, therefore, at low bias the carrier transport is dominated by direct quantum tunneling. [49] Note that in Figure 4, the ITO anode and the Al cathode have work functions of 4.7 and 4.3 eV (below the vacuum energy level), respectively. [50] The lowest unoccupied molecular orbital and highest occupied molecular orbital of TPBI have energy levels of 2.8 and 6.3 eV, respectively.…”

“…Several models had been employed to describe the carrier transport mechanism of the LEDs (especially organic LEDs), such as Fowler-Nordheim tunneling, Poole-Frenkel emission, trap-limited transport, space charge-limited current, and direct injection models. [45][46][47][48][49] For comparison, Figure 3b shows the fits of the measured J-V curve (V > 6.6 V) for device A by using Fowler-Nordheim tunneling (J ¼ a i V 2 Á expðÀb i =VÞ),…”

“…It can be seen that each curve can only be fitted by using different models at different regions of voltages, and this suggests that the carrier transport mechanism varies with bias voltage. Several models had been employed to describe the carrier transport mechanism of the LEDs (especially organic LEDs), such as Fowler–Nordheim tunneling, Poole–Frenkel emission, trap‐limited transport, space charge‐limited current, and direct injection models . For comparison, Figure b shows the fits of the measured J – V curve ( V > 6.6 V) for device A by using Fowler–Nordheim tunneling (), Poole–Frenkel emission (, and direct‐injection () models, respectively, where a and b are fitting constants determined by device parameters.…”