Metal halide perovskites have received much attention for their application in light-emitting diodes (LEDs) in the past several years. Rapid progress has been made in efficient green, red, and near-infrared perovskite LEDs. However, the development of blue perovskite LEDs is still lagging far behind. Here, we report efficient sky-blue perovskite LEDs by rearranging low-dimensional phase distribution in quasi-2D perovskites. We incorporated sodium ions into the mixed-Cl/Br quasi-2D perovskites with phenylethylammonium as the organic spacer and cesium lead halide as the inorganic framework. The inclusion of the sodium ion was found to significantly reduce the formation of the n = 1 phase, which was dominated by nonradiative transition, and increase the formation of other small-n phases for efficient exciton energy transfer. By managing the phase distribution, a maximum external quantum efficiency (EQE) of 11.7% was achieved in the sky-blue perovskite LED, with a stable emission peak at 488 nm. Further optimizing the phase distribution and film morphology with Pb content, we demonstrated the sky-blue devices with the average EQE approaching 10%. This strategy of engineering phase distribution of quasi-2D perovskites with a sodium ion could provide a useful way for the fabrication of high-performance blue perovskite LEDs.
Quasi-2D metal halide perovskites are promising candidates for light-emitting application owing to their large exciton binding energy and strong quantum confinement effect. Usually, quasi-2D perovskites are composed of multiple phases...
CsPbI3 is attractive for efficient and cost‐effective red perovskite light‐emitting diodes (PeLEDs), but its black phases still suffer from the metastable structure. The incorporation of large‐size organic cations has been widely used to construct quasi‐2D perovskites to stabilize the black phases. However, the multiple‐phase quasi‐2D perovskites usually show abundant interface defects and enhanced Auger recombination, leading to the low luminance and serious efficiency roll‐off in PeLEDs. Herein, highly efficient red PeLEDs are demonstrated with high luminance and low efficiency roll‐off realized by manipulating the crystallization kinetics of phenethylamine bromide (PEABr) incorporated CsPbI3. PEABr‐CsPbI3 nanocrystal films with much larger and more oriented β‐CsPbIxBr3‐x grains are successfully obtained through appropriately increasing PbI2 content and coordinating with anti‐solvent treatment. The carrier recombination dynamics investigations reveal that the trap‐assisted recombination and Auger recombination are greatly reduced in the passivation‐free PEABr‐CsPbI3 films by rational crystallization regulation. A peak external quantum efficiency (EQE) up to 19.6% is achieved in the red PeLEDs with a stable emission peak at 672 nm, which is maintained as high as 17.2% at a high luminance of over 1000 cd m−2. This study could shed light on modulating the crystallization kinetics of pervoskites to optimize carrier recombination dynamics toward high performance PeLEDs.
The
realization of electrically pumped organic semiconductor lasers
needs to suppress singlet–triplet annihilation (STA) as much
as possible. Generally, organic gain medium materials suffer extensive
loss of singlet excitons through STA, resulting in extremely high
lasing threshold current density (J
th)
on the order of 10–100 kA cm–2. Herein, we
study the lasing and electroluminescence (EL) properties of a new
organic gain material, named PIO, with low STA. As shown, it exhibits
remarkable optical gain and EL performance. A low lasing threshold
of 0.47 mJ cm–2 and a high Q-factor
of 6000 are well obtained in the microring resonator. In pulse-driven
organic light emitting diodes (OLEDs), a high current density of 112.4
A cm–2 is achieved. Furthermore, a dynamical model
is used to analysis exciton dynamics, gain behaviors and singlet exciton
loss channels under electrical excitation. It is found that the rate
of STA (k
ST) is at least lower than 1
× 10–10 cm3 s–1 to realize lasing emission with J
th below
the order of 10 kA cm–2. The k
ST of the doped PIO is determined to be 6.6 × 10–12 cm3 s–1. Therefore, it can be predicted
that the lasing threshold J
th of PIO is
about 1.20 kA cm–2.
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