维度依赖的色度调控新技术及其在低维单组份白光掺杂钙钛矿纳米晶电致发光器件的应用

White light halide perovskite nanocrystals is key for fabricating white electroluminescent LED with single type of active layer. For solving the problem of low photoluminescence quantum yields of white-emitted halide perovskiten anocrystals based on self-trapped excitons, this project brings out a new solution for white electroluminescent LED with high photoluminescence quantum yields by using doped halide perovskite nanocrystals with low dimensions. The content of the project includes the preparation of doped halide perovskite nanocrystals, the technique of dimensional-dependent color tuning, and the facrication of white electroluminescent LED. The Mn-Pb substitutional doping adoped in this project can not only make single component perovskite with white emission from both band gap and Mn impurities, but also avoid the low photoluminescence quantum yields for self-trapped excitons-induced white emission from deformable lattice and permenant lattice defects. By lowing the dimension of perovskite nanocrystals, the energy transfer from nanocrystals to Mn energy levels can be enhanced. This can avoid both the problems of increased nonirradiation recombination at high Mn doping amount and the issue of insufficent energy transfer efficicy at low Mn doping amount, and hence providing a new technique for tuning white emission. Since single component perovskite nanocrystals are used as the active layer for electroluminescent LED, the problems of fast halide exchange and failure to obtain white light by using different perovskite nanocrystals can be avoided. Our primary results have proved the effectiveness of dimensional-dependent color tuning. The final results of this project will promote the develepment of new emission color tuning technique by dimensions, and the investigation for Mn-Mn interactions and perovskite-Mn energy tranfer at different dimensions. This project will also provide a white LED with high quantum yields.

白光卤化铅钙钛矿纳米晶对组装单组份有源区白光发光器件至关重要。当前白光钙钛矿纳米晶是通过晶格变形和永久缺陷形成的自陷激子实现宽带白光，荧光效率较低。为获得高效白光器件，本项目提出以低维Mn掺杂钙钛矿制备白光LED的方案。内容包括低维掺杂钙钛矿制备、维度依赖的色度调控技术、白光LED器件组装。由于白色荧光来自带隙和替位杂质辐射复合、纳米晶缺陷态较少，从而解决了白光效率低的问题。利用低维纳米晶较弱的电磁屏蔽效应和较强的限域效应改善纳米晶-Mn能量转移效率，可解决高维度纳米晶在高掺杂下非辐射复合增加和低掺杂下能量转移效率不足的矛盾，为高效率白光的调制提供了新技术。以单组份白光纳米晶为有源区构建LED可解决多组份钙钛矿混合造成混色失败问题。项目前期进展已确认了维度对色度调控的有效性，其最终结果将推动色度调控技术、维度依赖的Mn-Mn作用及能量转移效率等问题的解决，提供一种高效率白光电致发光器件。

铅基卤化物钙钛矿由于荧光量子产率高、荧光发射峰窄、独特的缺陷容忍性、发射波长可覆盖整个可见光区等优异光学性质，成为光电功能材料领域热点材料之一。目前白光LED是通过将多种颜色荧光粉混合后制备，但这种荧光粉混合物普遍存在相位分离、色度偏移等缺点。利用紫外LED激发单组分的白色荧光粉是解决上述问题有效办法之一，而制备高荧光量子效率的白色荧光粉成为关键。本文围绕白色荧光卤化物钙钛矿纳米晶的制备及器件组装展开研究，利用具有量子限域效应的二维钙钛矿纳米晶及核-无定形壳结构零维卤化物钙钛矿纳米晶为宿主进行掺杂，克服了弱限域效应三维卤化物钙钛矿宿主材料中纳米晶-Mn杂质能量转移效率不足的缺点，实现了低掺杂量下较高的宿主-杂质能量转移效率，获得了具有白光发射能力的单一组分纳米材料。内容包括：.(1)以二维CsPbBr3纳米片为宿主材料，将MnCl2溶液加入纳米片中进行合成后掺杂，制备了二维掺杂钙钛矿纳米片。相比于尺寸超过波尔半径的三维钙钛矿纳米立方体，二维钙钛矿纳米片较薄的厚度极大加速了MnCl2分子向晶体内部的扩散过程，从而使MnCl2与CsPbBr3的分子交换过程从70小时（三维掺杂体系）缩短到10分钟（二维掺杂体系）。研究确定了Mn:Pb投料比在3-5之间时，纳米片色度处于暖白光区域。.(2)利用热注射法合成了零维核-无定形外壳Mn掺杂钙钛矿量子点。结果表明所制备的量子点可以在较低Mn掺杂量下（6.4%）实现较高的宿主-杂质能量转移效率，量子点导带-Mn能量转移速率常数是传统三维Mn: CsPb(Cl/Br)3纳米立方体的19.3倍。这种低掺杂量下高能量转移效率既可以避免高Mn掺杂量下Mn-Mn相互作用造成的荧光量子效率降低问题，也可以使宿主-杂质间能量转移满足白光纳米晶的要求,从而获得接近于标准白光的量子点。通过聚苯乙烯和量子点溶液混合制备了色度稳定的复合物，将复合物涂覆在紫外LED灯珠表面获得白光器件。.(3)将合成的单组分Mn掺杂的CsPb2ClxBr5-x纳米晶材料作为电致LED的发光层，搭建白光LED器件。该白光LED器件由ITO/PEDOT:PSS/PVK/Mn: CsPb2ClxBr5-x/ZnO/LiF/Al组成，这种结构设计使得来自阴极的电子和阳极的空穴能够在钙钛矿活性层进行高效率的复合发光。本研究为搭建基于单组份电致发光的白光钙钛矿LED器件提供新的思路。