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Abstract: A new series of four fluorene-thiophene copolymers, PF-co-2%TAQI, PF-co-5%TAQI, PF-co-10%TAQI and PF-co-15%TAQI, were synthesized by the Suzuki cross-coupling polymerization of 9,9-dihexylfluorene-2,7-dibromofluorene and N-butyl 6-[3-(2,5-dibromothienyl)]anthraquinone-2,3-dicarboxylic imide. The polymers have good solubility in common organic solvents and can form thin films by spin coating or casting. The UV–vis and photoluminescence (PL) spectra for the copolymers in dilute solution are similar to those of polyfluorene, i.e. maximum absorption at 381nm and 417nm and PL at 439nm. The UV–vis spectra of the polymer films also exhibit a single peak at 378nm, while an extra emission peak was found at 612nm, 618nm, 628nm and 626nm for PF-co-2%TAQI, PF-co-5%TAQI, PF-co-10%TAQI and PF-co-15%TAQI, respectively, presumably resulting from the excimer of anthraquinone imide groups. The electroluminescent properties of the copolymers were investigated using single-layer (ITO/PEDOT/Polymer/LiF/Al) and double-layer (ITO/PEDOT/Polymer/TPBi/LiF/Al) (TPBi, 1,3,5-Tris(1-phenyl-1H-benzimidazol-2-yl)benzene) LED devices. The double-layer devices based on copolymers emit multicolors under different voltages. The Commission Internationale de l’Eclairage (CIE) coordinates of PF-co-2%TAQI are (0.356, 0.249), (0.285, 0.210), (0.264, 0.277) and (0.240, 0.250) under 12V, 14V, 16V and 18V, respectively. [Copyright &y& Elsevier]

The balance of hole–electron injection is always a vital factor for the luminance, efficiency and working lifetime of quantum‐dot light‐emitting diodes (QLEDs), especially blue QLEDs. However, currently most approaches proposed to solve this issue involve tedious optimization of device architecture or material composition. Here, high‐performance blue QLEDs are reported based on CdZnS/ZnS quantum‐dot (QDs) by utilizing ZnO nanoparticles (NPs) and Al:Al2O3 as electron‐transporting layer (ETL) and cathode materials, respectively. The effect of post‐annealing temperature on the trap state density in ZnO NPs and the related mechanisms are investigated through optical and photoelectron spectroscopies. The method of controlling ZnO NPs annealing temperature leads to controllable electron‐mobility of ETL, which ultimately optimizes the balance of charge injection. Together with partially oxidized Al cathode (Al:Al2O3), high‐performance blue QLEDs are fabricated with luminance and external quantum efficiency (EQE) up to 27 753 cd m−2 and 8.92%. As far as is known, the peak luminance achieved is the record of deep blue QLEDs. This simple method for regulating charge injection balance via annealing temperature requires no modification of device architecture, making it applicable for a variety of QLEDs structures. High‐performance blue QLEDs are fabricated based on a ZnO nanoparticle (NP) electron‐transporting layer and a Al:Al2O3 cathode. The electron mobility in ZnO NP films can be regulated for better electron–hole balance by controlling the annealing temperature, thereby ensuring excellent luminance and recombination efficiency. This simple way to adjust charge injection balance requires no additional modification of the device architecture. [ABSTRACT FROM AUTHOR]

Quasi‐two‐dimensional (quasi‐2D) perovskites are attracting much attention due to their impressive luminescence properties. However, the introduction of insulating bulky cations reduces the charge transport property of mixed‐dimensional perovskites and leads to lowered brightness and increased turn‐on voltage. The trade‐off between high photoluminescence quantum yield (PLQY) and electrical conductivity should be well manipulated to obtain high‐performance perovskite light‐emitting diodes (PeLEDs). Herein, quasi‐2D perovskite BA2(CsPbBr3)n‐1PbBr4‐PEO with high PLQY and excellent carrier injection efficiency is demonstrated by incorporating bulky n‐butylammonium bromide (BABr), CsPbBr3, and polyethylene oxide (PEO). BA can intercalate into the three‐dimensional perovskite framework to form a layered (quasi‐2D) perovskite structure. The ion conductive polymer PEO is used to protect quasi‐2D perovskite crystals. Additional BABr is removed by using anhydrous isopropyl alcohol as a washing agent due to its selective dissolubility. By carefully modulating the optical and electrical properties of quasi‐2D perovskite films, the maximum luminance of PeLEDs is dramatically enhanced from 191 to 33533 cd m−2, which is the brightest green quasi‐2D PeLED reported thus far, leading to an increase in external quantum efficiency from 1.81% to 8.42%. This work provides a promising route to control the optical and electrical properties of quasi‐2D perovskite films for high‐performance optoelectronic devices. A quasi‐2D perovskite with high photoluminescence quantum yield and excellent carrier injection efficiency is demonstrated by incorporating n‐butylammonium bromide, CsPbBr3 and polyethylene oxide. By modulating the optical and electrical properties of quasi‐2D perovskite films, the maximum luminance of PeLEDs is dramatically enhanced from 191 to 33 533 cd m−2, which is the brightest value yet observed for green quasi‐2D PeLEDs. [ABSTRACT FROM AUTHOR]

Colloidal quantum dots light‐emitting diodes (QD‐LEDs) have been investigated for several decades. Compared with their green and red counterparts, the hole injection is more difficult for blue QDs due to their large optical band gap and relatively low highest occupied molecular orbital level. High‐performance blue QD‐LEDs are demonstrated by inserting a thin deoxyribonucleic acid (DNA) buffer layer between hole transport layer and ZnCdS/ZnS core/shell QDs layer. This DNA buffer layer can effectively enhance the hole injection efficiency, meanwhile its high lowest unoccupied molecular orbital level can help the injected electrons to be confined in the emitting layer, thus ensuring the charge balance in the QDs layer and an excellent recombination efficiency. After utilizing DNA as buffer layer, the maximum luminance is significantly increased from 10 218 to 16 655 cd m−2 and the external quantum efficiency is increased from 4.39% to 5.65%. These devices provide a saturated blue emission with emission peak located at 462 nm and full width at half maximum of 21 nm. This saturated blue emission makes it suitable for commercial applications. The results indicate that DNA is a promising material for regulating charge balance in the emitting layer for manufacturing high performance QD‐LEDs. Highly luminescent blue quantum‐dot (QD) light‐emitting diodes are successfully fabricated by introducing a thin deoxyribonucleic acid (DNA) interlayer between the hole transport layer and QDs emitting layer. The DNA buffer layer can effectively enhance the hole injection efficiency and confine the electrons in the emitting layer, thus ensuring the charge balance in the QDs layer and an excellent recombination efficiency. [ABSTRACT FROM AUTHOR]