ABSTRACT
Chiral-induced spin selectivity (CISS) effect provides innovative approach to spintronics and quantum-based devices for chiral materials. Different from the conventional ferromagnetic devices, the application of CISS effect is potential to operate under room temperature and zero applied magnetic field. Low dimensional chiral perovskites by introducing chiral amines are beginning to show significant CISS effect for spin injection, but research on chiral perovskites is still in its infancy, especially on spin-light emitting diode (spin-LED) construction. Here, the spin-QLEDs enabled by 2D chiral perovskites as CISS layer for spin-dependent carrier injection and CdSe/ZnS quantum dots (QDs) as light emitting layer are reported. The regulation pattern of the chirality and thickness of chiral perovskites, which affects the circularly polarized electroluminescence (CP-EL) emission of spin-QLED, is discovered. Notably, the spin injection polarization of 2D chiral perovskites is higher than 80% and the CP-EL asymmetric factor (gCP-EL ) achieves up to 1.6 × 10-2 . Consequently, this work opens up a new and effective approach for high-performance spin-LEDs.
ABSTRACT
Enhanced and balanced carrier injection is essential to achieve highly efficient green indium phosphide (InP) quantum dot light-emitting diodes (QLEDs). However, due to the poor injection of holes in green InP QLEDs, the carrier injection is usually balanced by suppressing the strong electron injection, which decreases the radiation recombination rate dramatically. Here, an electric dipole layer is introduced to enhance the hole injection in the green InP QLED with a high mobility electron transport layer (ETL). The ultra-thin MoO3 electric dipole layer is demonstrated to form a positive built-in electric field at the interface of the hole injection layer (HIL) and hole transport layer (HTL) due to its deep conduction band level. Simulation and experimental results support that strong electric fields are produced for efficient hole hopping, and the carrier recombination rate is substantially increased. Consequently, the green InP QLEDs based on enhanced electron and hole injection have achieved a high luminance of 52 730 cd m-2 and 1.7 times external quantum efficiency (EQE) enhancement from 4.25% to 7.39%. This work has provided an effective approach to enhance carrier injection in green InP QLEDs and indicates the feasibility to realize highly efficient green InP QLEDs.
ABSTRACT
As an effective manufacturing technology, inkjet printing is very suitable for the fabrication of perovskite light-emitting diodes in next-generation displays. However, the unsatisfied efficiency of perovskite light-emitting diode created with the use of inkjet printing impedes its development for future application. Here, we report highly efficient PeLEDs using inkjet printing, with an external quantum efficiency of 7.9%, a current efficiency of 32.0 cd/A, and the highest luminance of 2465 cd/m2; these values are among the highest values for the current efficiency of inkjet-printed PeLED in the literature. The outstanding performance of our device is due to the coffee-ring-free and uniform perovskite nanocrystal layer on the PVK layer, resulting from vacuum post-treatment and using a suitable ink. Moreover, the surface roughness and thickness of the perovskite layer are effectively controlled by adjusting the spacing of printing dots. This study makes an insightful exploration of the use of inkjet printing in PeLED fabrication, which is one of the most promising ways for future industrial production of PeLEDs.
ABSTRACT
The mechanisms for energy transfer including Förster resonance energy transfer (FRET) and radiative energy transfer in ternary-emissive system consists of blended-quantum dots (QDs, red-QDs blended with blue-QDs) emissive layer (EML) and blue-emissive hole-transport material that contained in quantum dot light-emitting diodes (QLEDs) are complicated. As the energy transfer could exhibit either positive or negative impact on QD's photoluminescence (PL) and electroluminescence (EL), it is important to analyze and modulate energy transfer in such ternary-emissive system to obtain high-efficiency QLEDs. In this work, we have demonstrated that proper B-QDs doping has a positive impact on R-QDs' PL and EL, where these improvements were attributed to the B-QDs' spacing effect on R-QDs which weakens homogeneous FRET among R-QDs and near 100% efficient heterogeneous FRET from B-QDs to R-QDs. With optimization based on the analysis of energy transfer, the PL quantum yield of blended-QDs (with R:B blending ratio of 90:10, in quality) film has been enhanced by 35% compared with that of unblended R-QDs film. Moreover, thanks to the spacing effect and high-efficiency FRET from B-QDs to R-QDs, the external quantum efficiency of QLEDs that integrate optimized blended-QDs (R:B=90:10) EML reaches 22.1%, which is 15% higher than that of the control sample (19.2%) with unblended R-QDs EML. This work provides a systematically analytical method to study the energy transfer in ternary-emissive system, and gives a valid reference for the analysis and development of the emerging QLEDs that with blended-QDs EML.
