基于二维ZnO纳米墙网络的高效钙钛矿LED的制备及发光特性研究

Due to the excellent properties including direct band-gap, high quantum efficiency, tunable emission wavelength and solution-processed method, etc., organic-inorganic hybrid perovskites have a great potential application in low-cost, high-brightness light-emitting diodes (LEDs). However, due to the difficulty in obtaining a complete coverage perovskite layer with a controllable morphology, and an absence of reasonable device configuration design for reduced interfacial potential barrier and effective carrier injection behavior, as well as a lack of incisive understanding on electroluminescent mechanisms of perovskite-based LEDs, there is still lack of significant breakthrough that can bring perovskite-based LEDs into the commercialization stage, such as a low external quantum efficiency and a relatively large turn-on voltage. Under such circumstance, we plan to fabricate a novel perovskite-based device structure, where high-quality two-dimensional ZnO nanowall networks are employed as the electron-supplying layer and a braced frame for a promoted surface coverage of CH3NH3PbX3 layer simultaneously. In addition, a Mg component gradually changed Zn(Mg)O layer is introduced between ZnO electron-supplying layer and CH3NH3PbX3 emissive layer as a graded electron barrier layer to improve the electron injection process; p-MgxNi1-xO materials with adjustable band-gap are used as the hole-supplying layer to achieve a reasonable energy band matching with CH3NH3PbX3 emissive layer. By using the well-designed device structure, the carrier injection and recombination efficiency are promoted substantially. This project will provide theoretical and experimental foundations for the fabrication and development of high-efficiency CH3NH3PbX3-based LEDs.

有机/无机杂化钙钛矿材料具有直接带隙、高内量子效率、带宽在可见光区连续可调以及可溶液制备等优良特性，在低成本、高亮度发光二极管（LED）领域具有巨大的应用潜力。然而，由于钙钛矿薄膜在表面覆盖率提升与微结构控制方面存在困难，已报道的器件结构在界面势垒调控和载流子平衡注入方面还有很大缺欠，加之目前对器件的电致发光机理认识还不够透彻，使得钙钛矿LED研究在改善器件外量子效率及开启电压等特性上遇到了瓶颈。由此，本项目提出构筑一种新的钙钛矿LED结构，采用二维ZnO纳米墙网络作为电子提供层，利用其纳米墙网络框架结构提升钙钛矿层的覆盖率并对膜层内纳米晶粒的尺寸进行调控，在ZnO与钙钛矿之间引入梯度Zn(Mg)O 势垒层优化电子的注入过程，同时利用带隙可调的p-MgxNi1-xO材料实现与钙钛矿层的合理能带匹配，以此提升载流子的注入和复合效率。该项目的开展将为高效钙钛矿LED的研制提供理论和实验依据。

有机/无机杂化钙钛矿材料具有直接带隙、高内量子效率、带宽在可见光区连续可调以及可溶液制备等优良特性，在低成本、高亮度发光二极管（LED）领域具有巨大的应用潜力。然而，由于钙钛矿薄膜在表面覆盖率提升与微结构控制方面存在困难，已报道的器件结构在界面势垒调控方面还有很大缺欠，加之目前对器件的电致发光机理认识还不够透彻，使得钙钛矿LED研究在改善器件外量子效率及开启电压等特性上遇到了瓶颈。由此，本项目提出构筑一种新的钙钛矿LED结构，采用二维ZnO纳米墙网络作为电子提供层，利用其纳米墙网络框架结构提升钙钛矿层的覆盖率并对膜层内纳米晶粒的尺寸进行调控，以期获得致密、均匀的钙钛矿薄膜。利用稳态和瞬态荧光测试，结合第一性原理计算，探究钙钛矿薄膜中多种辐射跃迁机制，并通过卤素离子置换反应实现材料发光波长的连续可调。基于有机-无机杂化CH3NH3PbBr3和无机CsPbBr3钙钛矿材料，申请人成功制备出了高性能的绿光LED，最大亮度为3809 cd·m−2，外量子效率为2.39%。在未封装、大气环境下，该器件可在直流驱动下连续工作10小时以上，发光强度衰减低于20%。此外，基于低成本、适用于大规模生产的全溶液工艺，申请人进一步对器件的温度/湿度稳定性进行提升。在高湿、高温环境下（75%相对湿度，120℃），器件可连续工作12 小时以上。进一步，申请人在器件结构中引入表面等离子体和同轴核壳结构理念，对器件的发光效率和工作稳定性进行了大幅改善，器件的外量子效率提升了55%，在空气环境下放置30天后仍可稳定工作。这些工作为新型、低成本钙钛矿LED的制备研究提供了可能的方案。