Fig. 1: Ultrahigh current densities and brightnesses realized with current-focusing, pulsed cg-QD LEDs.
From: Two-band optical gain and ultrabright electroluminescence from colloidal quantum dots at 1000 A cm−2
a An LED device stack used in the present work. An emitting layer of cg-QDs is sandwiched between a ZnMgO ETL and a TCTA HTL. The HTL is separated from the emitting layer by a current-focusing aperture (50-μm-wide slit) in a LiF interlayer. To enhance the current focusing effect, the Al anode is prepared as a 300-μm-wide strip, oriented orthogonally to the slit. b An optical microscope image of a biased device (V = 5.0 V) shows that the emitting area is confined to 300×50 μm2 dimensions. c The internal structure of the cg-QDs and the corresponding conduction- and valence-band (CB and VB, respectively) confinement potentials. d A simplified energy band diagram of the cg-QD-based LED and a schematic illustration of electron (blue arrow) and hole (red arrow) injections. e, f j−V (panel e) and L−V (panel f) characteristics of ‘planar’ (green triangles) and ‘current-focusing’ (blue squares and red circles) LEDs containing two layers of cg-QDs under d.c. (green triangles and blue squares) and pulsed (red circles) excitation. In the pulsed regime (τp = 1 μs, fp = 100 Hz), the current density reaches 1170 A cm−2. The corresponding peak brightness is 9.8 × 106 cd m−2.
