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
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
In blue quantum dot light emitting diodes(QLEDs),electron injection is insufficient,which would degrade device efficiency and stability.Herein,we employ chlorine passivated ZnO nanoparticles as electron transport laye...In blue quantum dot light emitting diodes(QLEDs),electron injection is insufficient,which would degrade device efficiency and stability.Herein,we employ chlorine passivated ZnO nanoparticles as electron transport layer to facilitate electron injection into QDs effectively.Moreover,it suppresses exciton quenching at the QD/ZnO interface by blocking charge transfer channel.As a result,the maximum external quantum efficiency of blue QLED was increased from 2.55%to 4.60%,and the operation lifetime of blue QLED was nearly 4 times longer than that of the control device.Our work indicates that election injection plays an important role in blue QLED efficiency and stability.展开更多
Display devices have significantly changed our daily life for decades,from the watches,television,to the laptop and smartphone.As the desire of advanced display device with high-resolution,long operation life and ligh...Display devices have significantly changed our daily life for decades,from the watches,television,to the laptop and smartphone.As the desire of advanced display device with high-resolution,long operation life and lightweight properties,several display techniques have been demonstrated.There are mainly four types of electronic display device:cathode ray tube(CRT),liquid-crystal display(LCD),organic light-emitting diode(OLED),and micro-LED.Due to the different working principles and device structures,each type of display device has its special characteristic properties.The performance of devices could be adjusted through the material selection or device design.With careful device structure regulation,not only the efficiency but also the stability would be improved.Herein,a brief review of innovative strategies towards the structure design is presented.展开更多
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.
基金Project supported by the National Key R&D Program of China(Grant Nos.2016YFB0401702 and 2017YFE0120400)the National Natural Science Foundation of China(Grant Nos.62005114,62005115,and 61875082)+5 种基金Key-Area Research and Development Program of Guangdong Province,China(Grant Nos.2019B010925001 and 2019B010924001)Guangdong University Key Laboratory for Advanced Quantum Dot Displays and Lighting(Grant No.2017KSYS007)Natural Science Foundation of Guangdong Province,China(Grant No.2017B030306010)Guangdong Basic and Applied Basic Research Foundation,China(Grant No.2019A1515110437)Shenzhen Peacock Team Project(Grant No.KQTD2016030111203005)High Level University Fund of Guangdong Province,China(Grant No.G02236004).
文摘In blue quantum dot light emitting diodes(QLEDs),electron injection is insufficient,which would degrade device efficiency and stability.Herein,we employ chlorine passivated ZnO nanoparticles as electron transport layer to facilitate electron injection into QDs effectively.Moreover,it suppresses exciton quenching at the QD/ZnO interface by blocking charge transfer channel.As a result,the maximum external quantum efficiency of blue QLED was increased from 2.55%to 4.60%,and the operation lifetime of blue QLED was nearly 4 times longer than that of the control device.Our work indicates that election injection plays an important role in blue QLED efficiency and stability.
基金Projects(71572028,71872027)supported by the National Natural Science Foundation of China。
文摘Display devices have significantly changed our daily life for decades,from the watches,television,to the laptop and smartphone.As the desire of advanced display device with high-resolution,long operation life and lightweight properties,several display techniques have been demonstrated.There are mainly four types of electronic display device:cathode ray tube(CRT),liquid-crystal display(LCD),organic light-emitting diode(OLED),and micro-LED.Due to the different working principles and device structures,each type of display device has its special characteristic properties.The performance of devices could be adjusted through the material selection or device design.With careful device structure regulation,not only the efficiency but also the stability would be improved.Herein,a brief review of innovative strategies towards the structure design is presented.
