金属/稀土上转换复合纳米结构中的等离激元荧光增强效应及其在薄膜太阳电池中的应用

We investigate plasmon enhanced fluorescence (PEF) in hybrid nanostructures composed of nano-metal and rare-earth-doped upconversion (UC) nanocrystals and its application in thin film solar cells. Shape, size, and phase-controlled UC materials with wide infrared absorption spectra are designed and synthesized using different rare earth ions co-doped in host material with chemical methods. New type and well-defined hybrid nano-metal/isolated layer/ UC nanocrystal superstructures are synthesized and characterized. Optical absorption spectra, UC emission spectra, transmission electron microscopy, and time-resolved photoluminescence are measured. The interaction between the incident laser, nano-phosphor and plasmon in these hybrid nanostructures is studied systemically. .Single metal particles or Au/Ag bimetal nanocomposites are fabricated by ordinary physical or chemical methods. Quasi-periodic metal nanostructures formed using these nano-metal are coupled with UC nanocrystals. The influence of the features (size, shape, distribution, and composition) of these nanostructures on surface plasmon resonance (SPR), local field enhancement (LFE), nonradiative resonant energy transfer and pumping threshold in the hybrid nanostructures is investigated. Calculations using Mie theory and Finite Difference Time Domain (FDTD) electromagnetic modeling methods are applied to analytically determine SPR and LEF. Moreover，we investigate the role of the isolate layer in PEF by changing its thickness and using different oxides (SiO2, TiO2, ZnO). The efficiency of the radiative decay rate and non-radiative coupling to the particle as well as their distance dependence is examines and established. .In order to fully characterize the radiative decay rate and enhanced electric fields at resonance, the size and shape of the metal particles, as well as the distance between the particles are needed to be controlled. The related parameters are designed using FDTD modeling. The designed templates are fabricated by electron beam lithography or focused ion beam milling technique. Ordered array templates are coupled with the synthesized UC nanocrystals. The detailed near-and far-field electromagnetic responses of metal periodic nanostructures are calculated using FDTD modeling. The electromagnetic coupling mechanisms between the emitter and the particle are studied by analyzing the role of the plasmon modes and their nature (dipole, multipole or interface mode). The dependence between the UC efficiency and the geometrical parameter of the ordered array template is investigated, providing insights into the role of localized and propagating plasmonic modes in the overall enhancement. The optimized UC superstructures are applied to thin film solar cells to investigate their responses to sub-bandgap infrared irradiation and improve the efficiency of the cells. New theoretical models for PEF will be developed based on both the experimental and theoretical results from this project.

研究纳米金属与稀土掺杂上转换纳米晶复合结构中激发光、纳米发光体以及等离激元相互作用新规律，探索基于纳米金属结构的新型上转换材料与薄膜光伏器件。具体包括，研究金属纳米结构/隔离层/稀土掺杂纳米晶复合结构体系的可控制备；研究准周期性金属纳米结构以及材料特性对复合结构中的表面等离激元共振频率的调制、局域电场的增强以及共振荧光的电荷、能量转移的途径和激发阈值的影响；研究纳米隔离层和周围环境对表面增强荧光和减少淬灭的影响；研究基于周期性金属纳米结构的复合体系中的等离激元光学现象和相关机理，可控地调节纳米金属的形状、大小、材料和结构周期，探索产生巨大荧光增强效应的本质；设计与制备上转换薄膜太阳电池，实现器件性能的提高；结合实验、理论研究结果，阐明表面荧光增强的物理机制，发展、完善表面荧光增强或淬灭的理论模型。作为基础研究，该课题将促进国内亚波长光子学、等离激元学、纳米发光材料和新型薄膜太阳电池的发展。

研究纳米金属与稀土掺杂上转换纳米晶复合结构中激发光、纳米发光体以及等离激元相互作用新规律，探索基于纳米金属结构的新型上转换材料与薄膜光伏器件。具体包括，研究金属纳米结构/隔离层/稀土掺杂纳米晶复合结构体系的可控制备；研究准周期性金属纳米结构以及材料特性对复合结构中的表面等离激元共振频率的调制、局域电场的增强以及共振荧光的电荷、能量转移的途径和激发阈值的影响；研究纳米隔离层和周围环境对表面增强荧光和减少淬灭的影响；研究基于周期性金属纳米结构的复合体系中的等离激元光学现象和相关机理，可控地调节纳米金属的形状、大小、材料和结构周期，探索产生巨大荧光增强效应的本质；设计与制备上转换薄膜太阳电池，实现器件性能的提高；结合实验、理论研究结果，阐明表面荧光增强的物理机制，发展、完善表面荧光增强或淬灭的理论模型；设计与制备了光转换纳米材料和等离激元光伏增强薄膜太阳电池，实现器件性能的显著提高，有光转换纳米材料或等离激元结构的薄膜太阳电池的光电转换效率相对传统的没有结构修饰的光伏器件提升了4.5%-14.5%；围绕新型、高性能纳米金属复合材料问题，提出并研发出分子束外延MBE大面积制备贵重金属单元和多元合金纳米粒子点阵制备技术，借助高性能、原子尺度分辨透射电镜TEM技术研究了贵重金属纳米团簇结构动力学，揭示了贵重金属纳米团簇结构动力学的新现象和机制；我们还将激光剥离技术引入到染料敏化太阳电池DSSC光阳极的制备工艺中，提出并研发出一种激光辅助低温膜转移法高性能DSSC光阳极制备技术，实现了高效率柔性DSSC器件的制备。该方法工艺简单、可重复性好、具有普适性，适用于多种导电基底，具有较大的应用潜力。作为基础研究，该课题将促进国内亚波长光子学、等离激元学、纳米发光材料和新型薄膜太阳电池的发展。