Two-band optical gain and ultrabright electroluminescence from colloidal quantum dots at 1000 A cm−2

Abstract

Colloidal quantum dots (QDs) are attractive materials for the realization of solution-processable laser diodes. Primary challenges towards this objective are fast optical-gain relaxation due to nonradiative Auger recombination and poor stability of colloidal QD solids under high current densities required to obtain optical gain. Here we resolve these challenges and achieve broad-band optical gain spanning the band-edge (1S) and the higher-energy (1P) transitions. This demonstration is enabled by continuously graded QDs with strongly suppressed Auger recombination and a current-focusing device design, combined with short-pulse pumping. Using this approach, we achieve ultra-high current densities (~1000 A cm−2) and brightness (~10 million cd m−2), and demonstrate an unusual two-band electroluminescence regime for which the 1P band is more intense than the 1S feature. This implies the realization of extremely large QD occupancies of up to ~8 excitons per-dot, which corresponds to complete filling of the 1S and 1P electron shells.

Frequency Stabilization and Optically Tunable Lasing in Colloidal Quantum Dot Superparticles

“…In particular, colloidal QDs are a highly studied medium for optical gain because their energetically well-separated, discrete electronic states theoretically promote low lasing thresholds, high-temperature stability, and large gain coefficients. − Since the first demonstrations of optical gain in QDs, , researchers have focused intensely on pragmatic designs for QD lasers, which have historically been impeded by fast, nonradiative Auger recombination in population-inverted QDs . There have been substantial efforts to reduce the effects of Auger recombination by synthesizing both thick-shelled core/shell QDs − (sometimes termed “giant nanocrystals”) and compositionally graded QDs. − …”

“…We note that collection times for the spectra in Figure are <1 s per spectrum (compared with multiple minutes of light exposure for the data in Figure ), so we do not observe any noticeable spectral instability in this data. Green emission at higher excitation fluenceboth from the 1P state and directly from the bulk-like CdS shell at bluer wavelengthshas been reported from thick-shelled QDs, , and optical fluence-tunable red/green lasing has been reported from microfabricated QD resonators but has not been demonstrated in solution-assembled SPs. The decrease in red lasing as the green lasing increases implies that green lasing from hot carriers occurs faster than carrier cooling, which is consistent with a previous report on tunable red/green lasing (where the green lasing occurs directly from the bulk-like CdS shell) …”

Optically Excited Lasing in a Cavity‐Based, High‐Current‐Density Quantum Dot Electroluminescent Device

“…The external quantum efficiency (EQE) of the device reaches 1.5% at 86 A cm −2 (Figure S6d, Supporting Information), which is comparable to EQEs of high‐ j devices with a traditional “optically lossy” MoO x /Ag anode. [ 36 ]…”

Blue‐Emitting Orthorhombic Boron Nitride Quantum Dots and Quantum‐Dot Light‐Emitting Diodes

“…[1][2][3][4] However, most of recent QLEDs are mainly Cd-based QDs and Pb-based perovskites. [5][6][7][8] The toxicity and accumulative nature of heavy metal Cd or Pb in these quantum dots (QDs) remain critical issues, which greatly limit their sustainable development. [9][10][11][12] Moreover, the performance of blue QLEDs is much lower compared with the red and green ones which have achieved great breakthrough.…”