The charge carrier transport and recombination dynamics in the quantum dots-based light-emitting diodes(QLEDs)featuring multiple emitting layers(M-EMLs)has a great impact on the device performance.In this work,QLEDs b...The charge carrier transport and recombination dynamics in the quantum dots-based light-emitting diodes(QLEDs)featuring multiple emitting layers(M-EMLs)has a great impact on the device performance.In this work,QLEDs based on M-EMLs separated by polyethyleneimine ethoxylated(PEIE)layer with different stacking sequences of blue(B),green(G),and red(R)QDs layer were used to intuitively explore the injection,transportation and recombination processes of the charge carriers in QLEDs by using the time-resolved electroluminescence(TrEL)spectra.From the TrEL spectra mea-surements,green and red emissions were obtained first in the QLEDs with the EMLs sequences of G/PEIE/B/PEIE/R and B/PEIE/R/PEIE/G along the direction of light emission,respectively.While the QLEDs adopt EMLs sequences of B/PEIE/G/PEIE/R,the blue,green and red emissions were obtained nearly at the same time.The above phenomenon can be attributed to different charge carrier transmission and radiation recombination process in the EMLs due to different valence band offsets and conduction band offsets between R-,G-and B-QDs by using different sequences of EMLs.White emission with coordi-nates of(0.31,0.31)and correlated color temperature(CCT)of 5916 K was obtained in the QLEDs with the EMLs se-quences of B/PEIE/G/PEIE/R,which can be attributed to the relative uniform emission of B-,G-and R-QDs due to the effec-tive injection and radiation recombination of charge carriers in each of the EMLs.The above results have great significance for further understanding and improving the performance of QLEDs with M-EMLs.展开更多
量子点是一种半导体纳米晶体,因其发光波长可调、颜色纯度高、色域广、寿命长、可溶液法制备受到广泛关注。量子点发光二极管(QLED)以其优越的发光性能、高效的能量转换效率,成为下一代平板显示、照明和可穿戴设备等领域的候选方案。顶...量子点是一种半导体纳米晶体,因其发光波长可调、颜色纯度高、色域广、寿命长、可溶液法制备受到广泛关注。量子点发光二极管(QLED)以其优越的发光性能、高效的能量转换效率,成为下一代平板显示、照明和可穿戴设备等领域的候选方案。顶发射是一种发光二极管结构,最后蒸镀的电极方向即为出光方向,不同于底发射,它的出光不需要经过驱动薄膜晶体管(TFT),因此其开口率高,是OLED/QLED显示的一种选择方案。顶发射QLED从顶电极一侧出光,因此,提高顶电极的出光效率是一个重要课题。通常在顶部电极上覆盖一层光提取层(Extraction Layer, EXL),调整功能层和光提取层之间的折射率差异,以提高出光率,同时采用光散射层(Scattering Layer, SCL)抑制微腔效应造成的出光角度不均匀问题。但是,通过调整功能层厚度来匹配光提取层折射率的方法会使得器件的电荷平衡性遭到破坏,同时现有的光散射层的制备过程涉及光刻、刻蚀等工艺,比较复杂,也易破坏器件功能层。基于此,本论文研究了光提取材料的筛选原则,使用了与量子点发光层折射率相匹配的光提取材料,优化光提取层厚度,提升了器件电流效率。另外,通过旋涂工艺,引入了光学纳米材料对出光施加散射,对比发现,粗糙度更大的纳米颗粒能够显著抑制光的角度分布不均匀问题。实验结果显示,优化后的顶电极结构使得器件的电流效率从14.8 cd/A提升到17.9 cd/A,而且器件的出光角度更加分散。Quantum dots are semiconductor nanocrystals that have garnered significant attention due to their tunable emission wavelengths, high color purity, wide color gamut, long lifetimes, and solution-processable fabrication. Quantum dot light-emitting diodes (QLEDs), renowned for their superior luminescent properties and high energy conversion efficiency, are emerging as potential candidates for next-generation flat-panel displays, lighting, and wearable devices. Top-emission is a type of light-emitting diode structure where the direction of the light emission corresponds to the direction of the final deposited electrode. Unlike bottom-emission, top-emission does not require the light to pass through the driving thin-film transistors (TFTs), resulting in a higher aperture ratio, making it a viable option for OLED/QLED displays. In top-emission QLEDs, light is emitted from the top electrode, making the improvement of the top electrode’s light extraction efficiency a critical issue. Typically, a light extraction layer (EXL) is applied over the top electrode to enhance light extraction by adjusting the refractive index difference between the functional layer and the light extraction layer. Additionally, a scattering layer (SCL) is used to mitigate the uneven light emission angle caused by the microcavity effect. However, adjusting the functional layer thickness to match the refractive index of the light extraction layer can disrupt the device’s charge balance. Furthermore, the current preparation process for scattering layers involves complex techniques like photolithography and etching, which can damage the functional layers of the device. In this context, the present study investigates the selection criteria for light extraction materials. By employing light extraction materials that match the refractive index of the quantum dot emission layer and optimizing the thickness of the light extraction layer, the device’s current efficiency is enhanced. Additionally, the introduction of optical nanomaterials via spin-coating applies scattering to the emitted light. Comparative analysis reveals that nanomaterials with greater roughness significantly suppress the uneven angular distribution of light. Experimental results demonstrate that the optimized top electrode structure increases the device’s current efficiency from 14.8 cd/A to 17.9 cd/A, while also achieving a more diffuse light emission angle.展开更多
目的:从文献计量角度分析了2001—2014年间的"QLED"研究发展。方法:基于Web of Science引文数据库,从发表论文数量的变化趋势、研究的国家/地区、研究机构和发表的期刊4个方面分析了2001—2014年国内外研究"QLED"...目的:从文献计量角度分析了2001—2014年间的"QLED"研究发展。方法:基于Web of Science引文数据库,从发表论文数量的变化趋势、研究的国家/地区、研究机构和发表的期刊4个方面分析了2001—2014年国内外研究"QLED"的分布情况。结果:年度发表论文的数量近几年发展迅速,从发文量和研究机构来看,美国、中国、韩国在该领域研究占领先地位,但在总被引频次和篇均被引频次方面,美国发表的论文遥遥领先。结论:中国在"QLED"研究的领域发展迅速,中科院的研究尤为突出,但与美国相比,还有一定的差距。展开更多
Poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt(4,4′-(N-(4-butylphenyl))](TFB),one of the most popular and widely used hole-transport layer(HTL)materials,has been successfully applied in high performance spin-coated quantum...Poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt(4,4′-(N-(4-butylphenyl))](TFB),one of the most popular and widely used hole-transport layer(HTL)materials,has been successfully applied in high performance spin-coated quantum dots-based light-emitting diodes(QLEDs)due to its suitable energy level and high mobility.However,there are still many challenging issues in inkjet-printed QLED devices when using TFB as HTL.TFB normally suffers from the interlayer mixing and erosion,and low surface energy against the good film formation.Here,a novel environment-friendly binary solvent system was established for formulating quantum dot(QD)inks,which is based on mixing halogen-free alkane solvents of decalin and n-tridecane.The optimum volume ratio for the mixture of decalin and n-tridecane was found to be 7:3,at which a stable ink jetting flow and coffee-ring free QD films could be formed.To research the influence of substrate surface on the formation of inkjet-printed QD films,TFB was annealed at different temperatures,and the optimum annealing temperature was found to enable high quality inkjet-printed QD film.Inkjet-printed red QLED was ultimately manufactured.A maximum 18.3%of external quantum efficiency(EQE)was achieved,reaching 93%of the spin-coated QLED,which is the best reported high efficiency inkjet-printed red QLEDs to date.In addition,the inkjet-printed QLED achieved similar T75 operational lifetime(27 h)as compared to the spin-coated reference QLED(28 h)at 2,000 cd·m−2.This work demonstrated that the novel orthogonal halogen-free alkane co-solvents can improve the interfacial contact and facilitate high-performance inkjet printing QLEDs with high EQE and stability.展开更多
Quantum dots (QDs) and QD-based light-emitting diodes(QLEDs) have been widely recognized as the key materials and devices for the next generation display due to their flexible and ultra-high definition characteristics...Quantum dots (QDs) and QD-based light-emitting diodes(QLEDs) have been widely recognized as the key materials and devices for the next generation display due to their flexible and ultra-high definition characteristics, and for color-controllable and healthy solid state lighting [1,2].The external quantum efficiency (EQE), brightness.展开更多
Developing light-emitting diodes(LEDs)with the merits of low driving and high brightness has always been attractive.Considering the carrier dynamic process under electroexcitation,the built-in potential(V_(bi))represe...Developing light-emitting diodes(LEDs)with the merits of low driving and high brightness has always been attractive.Considering the carrier dynamic process under electroexcitation,the built-in potential(V_(bi))represents the moment that the photons start to be produced in a LED.However,it has not been carefully studied and discussed.Here,we observed that by employing an interface regulation strategy to enhance hole concentration,the V_(bi)of quantum dot LEDs(QLEDs)can be reduced.Combined with the characterization methods of Mott–Schottky(MS)and scanning Kelvin probe microscopy(SKPM),the key indicator of V_(bi)on driving voltage for QLEDs is confirmed.Profiting from the reduction of V_(bi),a record-breaking ultra-low turn-on voltage of 2.2 V(@1 cd/m^(2))is achieved in a blue QLED.The blue QLED shows an advantage of high brightness under low driving voltages,i.e.,1000 cd/m^(2)@3.10 V and 5000 cd/m^(2)@3.88 V.This work proposes a reference strategy to predict and analyze the driving voltage issue,which is beneficial to facilitating the development of low-driving QLEDs in the future.展开更多
Perovskite quantum dot light-emitting diodes(Pe-QLEDs)have shown immense application potential in display and lighting fields due to their narrow full-width at half maximum(FWHM)and high photoluminescence quantum yiel...Perovskite quantum dot light-emitting diodes(Pe-QLEDs)have shown immense application potential in display and lighting fields due to their narrow full-width at half maximum(FWHM)and high photoluminescence quantum yield(PLQY).Despite significant advancements in their performance,challenges such as defects and ion migration still hinder their long-term stability and operational efficiency.To address these issues,various optimization strategies,including ligand engineering,interface passivation,and self-assembly strategy,are being actively researched.This review focuses on the synthesis methods,challenges and optimization of perovskite quantum dots,which are critical for the commercialization and large-scale production of high-performance and stable Pe-QLEDs.展开更多
文摘The charge carrier transport and recombination dynamics in the quantum dots-based light-emitting diodes(QLEDs)featuring multiple emitting layers(M-EMLs)has a great impact on the device performance.In this work,QLEDs based on M-EMLs separated by polyethyleneimine ethoxylated(PEIE)layer with different stacking sequences of blue(B),green(G),and red(R)QDs layer were used to intuitively explore the injection,transportation and recombination processes of the charge carriers in QLEDs by using the time-resolved electroluminescence(TrEL)spectra.From the TrEL spectra mea-surements,green and red emissions were obtained first in the QLEDs with the EMLs sequences of G/PEIE/B/PEIE/R and B/PEIE/R/PEIE/G along the direction of light emission,respectively.While the QLEDs adopt EMLs sequences of B/PEIE/G/PEIE/R,the blue,green and red emissions were obtained nearly at the same time.The above phenomenon can be attributed to different charge carrier transmission and radiation recombination process in the EMLs due to different valence band offsets and conduction band offsets between R-,G-and B-QDs by using different sequences of EMLs.White emission with coordi-nates of(0.31,0.31)and correlated color temperature(CCT)of 5916 K was obtained in the QLEDs with the EMLs se-quences of B/PEIE/G/PEIE/R,which can be attributed to the relative uniform emission of B-,G-and R-QDs due to the effec-tive injection and radiation recombination of charge carriers in each of the EMLs.The above results have great significance for further understanding and improving the performance of QLEDs with M-EMLs.
文摘量子点是一种半导体纳米晶体,因其发光波长可调、颜色纯度高、色域广、寿命长、可溶液法制备受到广泛关注。量子点发光二极管(QLED)以其优越的发光性能、高效的能量转换效率,成为下一代平板显示、照明和可穿戴设备等领域的候选方案。顶发射是一种发光二极管结构,最后蒸镀的电极方向即为出光方向,不同于底发射,它的出光不需要经过驱动薄膜晶体管(TFT),因此其开口率高,是OLED/QLED显示的一种选择方案。顶发射QLED从顶电极一侧出光,因此,提高顶电极的出光效率是一个重要课题。通常在顶部电极上覆盖一层光提取层(Extraction Layer, EXL),调整功能层和光提取层之间的折射率差异,以提高出光率,同时采用光散射层(Scattering Layer, SCL)抑制微腔效应造成的出光角度不均匀问题。但是,通过调整功能层厚度来匹配光提取层折射率的方法会使得器件的电荷平衡性遭到破坏,同时现有的光散射层的制备过程涉及光刻、刻蚀等工艺,比较复杂,也易破坏器件功能层。基于此,本论文研究了光提取材料的筛选原则,使用了与量子点发光层折射率相匹配的光提取材料,优化光提取层厚度,提升了器件电流效率。另外,通过旋涂工艺,引入了光学纳米材料对出光施加散射,对比发现,粗糙度更大的纳米颗粒能够显著抑制光的角度分布不均匀问题。实验结果显示,优化后的顶电极结构使得器件的电流效率从14.8 cd/A提升到17.9 cd/A,而且器件的出光角度更加分散。Quantum dots are semiconductor nanocrystals that have garnered significant attention due to their tunable emission wavelengths, high color purity, wide color gamut, long lifetimes, and solution-processable fabrication. Quantum dot light-emitting diodes (QLEDs), renowned for their superior luminescent properties and high energy conversion efficiency, are emerging as potential candidates for next-generation flat-panel displays, lighting, and wearable devices. Top-emission is a type of light-emitting diode structure where the direction of the light emission corresponds to the direction of the final deposited electrode. Unlike bottom-emission, top-emission does not require the light to pass through the driving thin-film transistors (TFTs), resulting in a higher aperture ratio, making it a viable option for OLED/QLED displays. In top-emission QLEDs, light is emitted from the top electrode, making the improvement of the top electrode’s light extraction efficiency a critical issue. Typically, a light extraction layer (EXL) is applied over the top electrode to enhance light extraction by adjusting the refractive index difference between the functional layer and the light extraction layer. Additionally, a scattering layer (SCL) is used to mitigate the uneven light emission angle caused by the microcavity effect. However, adjusting the functional layer thickness to match the refractive index of the light extraction layer can disrupt the device’s charge balance. Furthermore, the current preparation process for scattering layers involves complex techniques like photolithography and etching, which can damage the functional layers of the device. In this context, the present study investigates the selection criteria for light extraction materials. By employing light extraction materials that match the refractive index of the quantum dot emission layer and optimizing the thickness of the light extraction layer, the device’s current efficiency is enhanced. Additionally, the introduction of optical nanomaterials via spin-coating applies scattering to the emitted light. Comparative analysis reveals that nanomaterials with greater roughness significantly suppress the uneven angular distribution of light. Experimental results demonstrate that the optimized top electrode structure increases the device’s current efficiency from 14.8 cd/A to 17.9 cd/A, while also achieving a more diffuse light emission angle.
文摘目的:从文献计量角度分析了2001—2014年间的"QLED"研究发展。方法:基于Web of Science引文数据库,从发表论文数量的变化趋势、研究的国家/地区、研究机构和发表的期刊4个方面分析了2001—2014年国内外研究"QLED"的分布情况。结果:年度发表论文的数量近几年发展迅速,从发文量和研究机构来看,美国、中国、韩国在该领域研究占领先地位,但在总被引频次和篇均被引频次方面,美国发表的论文遥遥领先。结论:中国在"QLED"研究的领域发展迅速,中科院的研究尤为突出,但与美国相比,还有一定的差距。
基金This work was supported by the National Key Research and Development Program of China(No.2016YFB0401600)the National Natural Science Foundation of China(No.U1605244)China Postdoctoral Science Foundation(No.2020M681726).
文摘Poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt(4,4′-(N-(4-butylphenyl))](TFB),one of the most popular and widely used hole-transport layer(HTL)materials,has been successfully applied in high performance spin-coated quantum dots-based light-emitting diodes(QLEDs)due to its suitable energy level and high mobility.However,there are still many challenging issues in inkjet-printed QLED devices when using TFB as HTL.TFB normally suffers from the interlayer mixing and erosion,and low surface energy against the good film formation.Here,a novel environment-friendly binary solvent system was established for formulating quantum dot(QD)inks,which is based on mixing halogen-free alkane solvents of decalin and n-tridecane.The optimum volume ratio for the mixture of decalin and n-tridecane was found to be 7:3,at which a stable ink jetting flow and coffee-ring free QD films could be formed.To research the influence of substrate surface on the formation of inkjet-printed QD films,TFB was annealed at different temperatures,and the optimum annealing temperature was found to enable high quality inkjet-printed QD film.Inkjet-printed red QLED was ultimately manufactured.A maximum 18.3%of external quantum efficiency(EQE)was achieved,reaching 93%of the spin-coated QLED,which is the best reported high efficiency inkjet-printed red QLEDs to date.In addition,the inkjet-printed QLED achieved similar T75 operational lifetime(27 h)as compared to the spin-coated reference QLED(28 h)at 2,000 cd·m−2.This work demonstrated that the novel orthogonal halogen-free alkane co-solvents can improve the interfacial contact and facilitate high-performance inkjet printing QLEDs with high EQE and stability.
文摘Quantum dots (QDs) and QD-based light-emitting diodes(QLEDs) have been widely recognized as the key materials and devices for the next generation display due to their flexible and ultra-high definition characteristics, and for color-controllable and healthy solid state lighting [1,2].The external quantum efficiency (EQE), brightness.
基金support was from the National Key Research and Development Program of China(No.2022YFB3606502)the National Natural Science Foundation of China(Nos.52131304,62004101,62261160392,and 22022205)+1 种基金Jiangsu graduate and practice innovation program(No.KYCX23_0456)the Fundamental Research Funds for the Central Universities(No.30920041117).
文摘Developing light-emitting diodes(LEDs)with the merits of low driving and high brightness has always been attractive.Considering the carrier dynamic process under electroexcitation,the built-in potential(V_(bi))represents the moment that the photons start to be produced in a LED.However,it has not been carefully studied and discussed.Here,we observed that by employing an interface regulation strategy to enhance hole concentration,the V_(bi)of quantum dot LEDs(QLEDs)can be reduced.Combined with the characterization methods of Mott–Schottky(MS)and scanning Kelvin probe microscopy(SKPM),the key indicator of V_(bi)on driving voltage for QLEDs is confirmed.Profiting from the reduction of V_(bi),a record-breaking ultra-low turn-on voltage of 2.2 V(@1 cd/m^(2))is achieved in a blue QLED.The blue QLED shows an advantage of high brightness under low driving voltages,i.e.,1000 cd/m^(2)@3.10 V and 5000 cd/m^(2)@3.88 V.This work proposes a reference strategy to predict and analyze the driving voltage issue,which is beneficial to facilitating the development of low-driving QLEDs in the future.
文摘Perovskite quantum dot light-emitting diodes(Pe-QLEDs)have shown immense application potential in display and lighting fields due to their narrow full-width at half maximum(FWHM)and high photoluminescence quantum yield(PLQY).Despite significant advancements in their performance,challenges such as defects and ion migration still hinder their long-term stability and operational efficiency.To address these issues,various optimization strategies,including ligand engineering,interface passivation,and self-assembly strategy,are being actively researched.This review focuses on the synthesis methods,challenges and optimization of perovskite quantum dots,which are critical for the commercialization and large-scale production of high-performance and stable Pe-QLEDs.
