All-Solution-Processed Quantum Dot Light Emitting Diodes Based on Double Hole Transport Layers by Hot Spin-Coating with Highly Efficient and Low Turn-On Voltage

Abstract

Poly( N, N'-bis(4-butylphenyl) N, N'-bis(phenyl)benzidine) (poly-TPD) and poly(9-vinylcarbazole) (PVK) are both traditional hole transport layers (HTLs) in quantum dot light emitting diodes (QLEDs). Nevertheless, the low highest occupied molecular orbital of poly-TPD and poor hole mobility of PVK always result in poor performance of QLEDs when individually used as HTLs. Unfortunately, fabricating stepwise HTLs with poly-TPD and PVK faces technical problems until now. We demonstrate an effective method to construct the stepwise poly-TPD and PVK HTLs by utilizing the technique of hot spin-coating PVK in m-xylene on poly-TPD film. During this hot spin-coating process, the underlying poly-TPD remains unwashed and undamaged, benefiting the all-solution-processed QLED fabrication. The optimized all-solution-processed QLED with stepwise poly-TPD and PVK HTLs shows a maximum external quantum efficiency (EQE) of 15.3% and a maximum luminance of 17 110 cd/m with a low turn-on voltage ( V) of 1.75 V. The maximum EQE is about 6.6 times higher than that of the reference QLED using a cold spin-coating process. The enhancement of the QLED performance can be attributed to the improvement of surface morphology and charge injection balance for the hot spin-coating stepwise co-HTLs based QLEDs. This work manifests the positive effect on performance boost by a hot spin-coating strategy toward stepwise co-HTLs formation and paves the way to fabricate highly efficient all-solution-processed light emitting diodes.

Efficient and Spectrally Stable Blue Perovskite Light‐Emitting Diodes Based on Potassium Passivated Nanocrystals

“…The energy level diagram of the device and the related electroluminescence (EL) characterization is presented in Figure S7 (Supporting Information). The valance band of the perovskite films is confirmed via ultraviolet photoelectron spectroscopy (UPS) as shown in Figure S8 (Supporting Information), whereas the others are obtained from literatures . The current density–voltage–luminance curves are shown in Figure S7b (Supporting Information), where a higher current density and luminescence can be observed in the K + ‐based devices.…”

“…Consequently, the maximum EQE is enhanced from 1.19% to 1.63% for the champion device (Figure S11, Supporting Information). Additionally, we use a bilayer HTL of poly‐TPD and poly(9‐vinylcarbazole) (PVK) to promote hole injection further . The energy level and schematic diagram of the device are presented in Figure a,b, respectively.…”

Sodium Ion Modifying In Situ Fabricated CsPbBr3 Nanoparticles for Efficient Perovskite Light Emitting Diodes

“…When the PVK film is spin coated from 8 mg mL −1 chlorobenzene (CB) solution, the LEDs device possesses the best performance. It is conjectured that too thick of PVK may restrict hole injection owing to the lower hole mobility of PVK . To confirm it, the hole‐only devices with the structure of ITO/NiO x (/PVK)/CsPbBr 3 NPs/Au are made and the J – V curves are plotted in Figure S14b (Supporting Information), which indicates the hole injection property gets worse indeed with the increase of PVK thickness.…”

Optimization of the electron transport layer in quantum dot light-emitting devices

“…This recombination has a significant role in electroluminescent devices. Recently, published works exhibit an external quantum efficiency of~20% for CdSe \CdS QLED devices [7][8][9] . However, the heavy metal ion cadmium (Cd) raises health concerns and requires corresponding environmental regulations 9,10 .…”