基于光谱转换和波导的高效率荧光聚光器件及其关键材料研究

A novel high efficiency Luminescent Solar Concentrator (LSC) based on spectrum conversion and photonic crystal waveguides is proposed and required materials are studied. Like conventional LSCs, photoluminescent particles absorb the solar spectrum and re-emit narrow-band, near-infrared light, which is confined in a wave guide plate that consists of 3D photonic crystals and high-index glasses. The wave guide plate significantly reduces or eliminates the light escape, which dramatically increases the flux gain of the LSC. Ideal fluorescent materials have high absorption over the solar spectrum, narrow emission at near infrared region above the band gap of a high efficiency PV, where the absorption edge and the emission peak are well separated (therefore low self-absorption coefficient), and high emission quantum efficiency. Combinatorial Materials Synthesis and Characterization, a high-throughput materials screening technique, will be used to search such materials. The wave guide will be designed based on the photonic crystal diffraction theory using computer simulations, and fabricated using Holographic Laser Patterning method based on multi-beam laser interference. An ideal LSC should prevent the loss of flux gain due to re-absorption and leaking through the escape cone of the wave guide, the latter becomes dominant factor that renders the flux gain much less than the geometric gain of the 2-D waveguide. All traditional LSCs fail to confine the emission light loss from escape cone and result in a maximum flux gain of only ~10X regardless of the geometric gains. The proposed LSC addresses the limiting factors and improves the gain to more than 100X by understanding the detailed optical loss mechanisms, establishing a quantitative device model, and developing appropriate materials and structures. The proposed research has great impacts on understanding the physics of LSCs, improving its optical concentration and efficiency, and eventually leading to low cost and widespread utilizations of solar energy.

本项目采用"高通量组合材料制备与表征技术"研究高性能无机光致发光材料，具备吸收谱宽且吸收系数大，发射谱窄且与吸收谱不重叠，量子效率高，在介质材料中溶解度高，稳定性好等优点，实现广谱可见光向近红外窄带荧光的高效率转换。利用三维光子晶体实现荧光光子的波导式传播，并组装荧光太阳能聚光器件（简称LSC），其光子增益可超过传统器件100倍以上。通过上述关键材料和器件的研究，建立以性能预测为导向的LSC器件优化物理模型，探索和解决制约LSC器件发展的关键科学问题，阐明LSC器件的光子增益及量子效率损失机制、荧光材料吸收边和发射峰的缺陷调制机制、光子晶体对特定荧光光子的约束机制，为高效LSC器件奠定理基础。同时，我们以寻找特定无机荧光材料为目标制定光电子材料设计的基本路线，完善其高通量搜索和快速研制方法学，以偏折特定波长荧光为目标探索三维光子晶体设计方法学，建立多束激光全息干涉制备方法学。

近年来，太阳能发电作为目前最重要以及最有前途的清洁能源发电方式之一，吸引了广泛关注。然而，在城市建筑中，传统太阳能电池板只能利用面积有限的屋顶铺设，限制了分布式太阳能发电装置的普及。采用荧光太阳能聚光器件（Luminescent Solar Concentrators，LSC）发电技术是利用荧光聚光器吸收漫反射或直射的太阳光，并利用荧光材料将量子效率较低的自然光转换为量子效率较高的荧光，最后利用荧光在波导内发生全反射将其汇聚导入到波导四周太阳能电池板中产生电流。LSC技术被提出已有数十年的历史，受限于荧光材料较低的发光效率与荧光波导荧光逃逸的问题，还未能实现大规模应用。本项目从LSC器件的聚光效率计算入手，通过计算与初步筛选，选择了Al2O3: Cr3+无机荧光材料体系；随后，设计、开发了高通量磁控溅射薄膜沉积系统，利用梯度溅射的方法，制备了Al2O3: Cr3+组合材料芯片，通过同步辐射XRD与XPS表征了样品的结构与成分信息，利用荧光分光光度计表征了薄膜样品的发光性能，根据表征结果研究了Al2O3: Cr3+材料体系的构效关系，并筛选出了性能最好的材料成分；采用双螺旋挤出的方法与原位聚合的方法，制备了PMMA聚光波导，并优化了器件的几何尺寸；采用旋涂和浸渍提拉的方法制备了TiO2光子晶体薄膜，在一定程度上实现了对荧光逃逸的消除；最后，利用Al2O3: Cr3+作为荧光材料设计、组装出LSC器件，并与以有机小分子材料为荧光物质的LSC器件进行了性能对比，为该LSC器件的实际应用提供了基本的认识。上述成果表明，本项目的系列研究成果为LSC器件新材料、新器件的设计与研究提供了新思路，在分布式发电领域具有重要的应用前景。另外，本项目相关材料的高通量实验研究方法与技术有望为更广泛的新材料设计与性能优化提供有力支撑。