基于表面工程的钙钛矿/氧化物核/壳纳米结构的制备及发光性能研究

Metal halide perovskites (MHPs) have potential applications in luminescence and display because of numerous advantages such as high photoluminescence quantum efficiency, very narrow emission linewidth, low material cost and solution processability. Despite rapid progress in MHPs, low stability has long been the main obstacle hindering the practical application of these materials. We would like to synthesize MHPs nanocrystals (MHPs NPs) by hot injection and precipitation methods with the assistance of ammonium halides with double long alkyl chains as both capping ligands and halide precursors. On the one hand, it is reported that replacement of Cs+ with ammonium will enhance the interactions between ligands and the MHPs surface. Interactions among the ligand moleculars will be also strengthened due to increased alkyl chains. On the other hand, more halide ions will be remained on the surface of MHPs NPs. As a result, the photoluminescent properties and stability of MHPs NPs would be greatly improved and thus the MHPs NPs could be dispersed in polar solvents such as ethanol stably. With the help of surface modification with alkoxy silane, MHPs/oxides core-shell nanostructures would be produced by hydrolysis of silicon, titanium and tin alkoxides. Absorption and Photoluminescence spectra of these core-shell nanostructures will be recorded upon excitation by continuous light source or pulsed laser. The influence of capping ligands, the compositions and thicknesses of the oxides shells on the electronic structure, photoluminescence quantum efficiency (PLQE), lifetime and binding energy of exciton will be investigated in details. Based on these experimental results, we will fabricate several MHPs-based luminescent nanomaterials with high PLQE and stability.

卤化物钙钛矿纳米材料具有高发光量子效率、窄发射半峰宽、成本低廉、易于制备加工等特性，在发光和显示等领域具有广泛的应用前景，但是稳定性差一直是限制其实际应用的瓶颈。本项目拟采用含有双烷基链的卤化铵盐作为卤素前驱体和表面配体来制备卤化物钙钛矿纳米材料，既可以增强颗粒表面与配体之间、配体和配体之间的相互作用实现纳米颗粒表面的钝化，又易于形成富卤离子表面，提高其发光性能和稳定性，实现在极性溶剂中的稳定分散。以此为基础，借助长烷基链硅烷表面改性方法，通过水解/醇解反应在纳米颗粒表面进行氧化物壳层的包覆，制备钙钛矿/氧化物核/壳纳米结构。对这些纳米结构进行稳态和时间分辨吸收和发光光谱表征，系统研究表面配体、氧化物组成和厚度对电子结构、发光量子效率、发光动力学和激子结合能的影响，揭示影响钙钛矿纳米材料发光性能的表、界面因素，合成高稳定性、高效发光的卤化物钙钛矿纳米材料，加速其实际应用进程。

卤化物钙钛矿纳米材料具有高发光量子效率、窄发射半峰宽、成本低廉、易于制备加工等特性，在发光和显示等领域具有广泛的应用前景，但是稳定性差一直是限制其实际应用的瓶颈。本项目通过制备过程中的表面配体和组成调控，合成了多种CsPbX3（X = Cl/Br/I）钙钛矿纳米颗粒，研究了表面配体和组成等对纳米颗粒在极性溶剂、光照和加热过程中稳定性的影响，探究了表面钝化的机制。发现双烷基链卤化铵盐的引入，不仅提高了CsPbBr3纳米颗粒表面配体层的致密程度，而且可以在适当反应条件下引入类PbBr2吸附层实现表面钝化，使其在极性溶剂中的稳定性得到显著增强；CsPbX3钙钛矿纳米颗粒的表面组成是影响其光稳定性的关键因素，可以通过后处理实现表面光诱导自钝化，显著提升光稳定性。多烷基取代的硅烷配体不仅可以保护CsPbX3纳米颗粒免受极性溶剂侵蚀，而且可以诱导生成热力学稳定的正交相CsPbI3纳米颗粒。更重要的是，硅烷类配体可以作为有效连接剂，使多种氧化物的前驱体水解/醇解反应产物在纳米颗粒表面生长，发展了CsPbX3钙钛矿纳米颗粒表面包覆氧化物壳层的通用策略。通过稳态/时间分辨吸收和光致发光光谱等测试，研究了氧化物壳层对钙钛矿纳米颗粒的激子吸收和发射性能的影响，并开展了包覆前后纳米颗粒在含水溶剂、光照和加热过程中稳定性的比较研究，发现这些CsPbX3/氧化物核/壳结构在含水溶剂和加热过程都表现出了显著提升的稳定性。项目实施以来，共发表SCI论文5篇，北大核心中文期刊1篇，申请并获得国家发明专利授权2项，为高稳定金属卤化物钙钛矿纳米颗粒的合成提供了行之有效的方法。培养博士毕业生3名（含共同培养1名），硕士毕业生3名。