Fig. 1. (Color online) (a) An illustration of how quantum confinement affects the energy level distribution near the band edge of QDs. (b) Deviation of the Gaussian HOMO and LUMO of QDs and NCs. When the QD size approaches or becomes smaller than two times of the exciton Bohr radius (2r_B), the spatial restriction of electron and hole wavefunctions leads to significant quantum confinement, which results in discrete energy levels, bandgap widening, and enhanced exciton binding energies. Conversely, QDs with dimensions significantly larger than the 2r_B exhibit weaker confinement, where their properties begin to resemble those of bulk semiconductors.

Fig. 2. (Color online) (a) and (b) are TEM images of QD and NC, respectively. (c) and (e) are high-resolution TEM images of QD and NC, respectively. (d) and (f) are size distribution histograms of QD and NC, respectively.

Fig. 3. (Color online) (a) UV−vis absorption and PL (365 nm excitation wavelength) spectra of NC and QD. (b) TRPL decay curves of NC and QD.

Fig. 4. (Color online) (a) and (b) are UPS spectra of NC film and QD film deposited on ITO glass substrates, respectively. (c) Tauc plots of NC and QD. (d) Device structure of the hole-only device and (e) its corresponding energy band diagram. (f) J−V curves of hole-only devices.

Fig. 5. (Color online) (a) Schematic of the LED architecture and the corresponding (b) energy band diagram.

Fig. 6. (Color online) (a) Current density and brightness vs driving voltage of LEDs employing NC, QD, and MIX emitters. (b) Current density vs brightness curves of LEDs. (c) External quantum efficiency vs current density of LEDs. (d) Mott–Schottky plots of capacitance–voltage characterization for LEDs.

Fig. 7. (Color online) (a) Voltage-dependent EL spectra of LEDs, with photo of working devices at their peak brightness as insets. (b) Evolution of the normalized EL signal of working LEDs under nitrogen atmosphere at an initial brightness of 100 cd·m⁻².