自掺杂硫化亚铜纳米晶体等离激元效应及其在CIGS薄膜太阳能电池中的应用研究

Copper chalcogenide is a kind of earth abundant and environment-friendly crystalline material, which is also the building block of new-generation thin film solar cells. Recently, localized surface plasmon resonance (LSPR) was found in heavily self-doped copper(I) sulfide (Cu2-xS) nanocrystals, which was previously considered only existing in noble metal nanoparticles. Furthermore, their resonant frequency, which is fixed in noble metal particles, is variable by modifying cation vacancies. Herein, we propose to systematically study the LSPR properties of Cu2-xS nanocrystals, then introduce them into high-performance CIGS thin film solar cells. The reasons are those: Cu2-xS nanocrystals are capable to acutely scatter the incident light under resonant condition; Strong near field enhancement occurs around dispersed nanocrystals as well. Both of these phenomenon arise from LSPR. So it is proposed that to take these advantages in enhancing the optical absorption of existing CIGS photovoltaic structures, by modifying the device structures with adding proper Cu2-xS components and optimizing their structural parameters related to the above two effects. In addition, the density of cation vacancies will be adjusted on purpose of optimizing the spectral overlapping between LSPR response of Cu2-xS nanocrystals and solar response of CIGS cell, and improving absorption efficiency in near infrared area. All the above proposals aim to fabricate high-performance and low-cost plasmonic CIGS thin film solar cell in the future.

铜硫化合物是一类地球富集的环境友好型晶体材料，是新一代薄膜太阳能电池的基本原料。自掺杂的硫化亚铜（Cu2-xS）纳米晶体最近被发现具有类似于贵金属纳米颗粒的局域表面等离子体共振（LSPR）效应。更重要的是，与贵金属纳米颗粒不同，其共振频率能够通过阳离子空位掺杂浓度调节。由此，本项目提出对Cu2-xS纳米晶体的LSPR性质进行系统性研究，并将其用于提高铜铟镓硒（CIGS）薄膜太阳能电池的光电转换效率。其根据是：Cu2-xS纳米晶体在共振条件下对入射光的散射效果和表面近场增强效应均可以被用于提高CIGS薄膜的光吸收效率。因此可以针对这两点进行参数优化，并以现有CIGS薄膜电池结构为基础构造光吸收效率经LSPR增强的电池器件。其中，可以通过调节空位掺杂浓度，使共振频率更好地匹配CIGS电池对太阳光的响应谱线。以上为未来实现高效率、低成本的光伏器件提供理论支持和实验基础。

自掺杂硫化亚铜（Cu2-xS）纳米晶体材料是近年来被发现具有类似于贵金属的局域表面等离子体共振（Localized Surface Plasmon Resonance, LSPR）效应的半导体纳米材料，并且其共振波长可以经由自掺杂空位浓度精确控制，因此具有应用于增强薄膜太阳能电池效率的巨大潜力。本项目首先以时域有限差分方法（FDTD）作为基础，对不同尺寸和形状的Cu2-xS纳米晶体的LSPR共振吸收峰位和峰宽进行模拟，并在此基础上优化纳米晶体结构参数。通过液相方法合成了尺寸和组分可控的胶态Cu2-xS纳米晶体颗粒，其与LSPR相关的光吸收性能符合预期；通过改进的液相方法直接合成了高溶解性CZT(S,Se)多元胶态纳米晶体，经由表面换链工艺后，通过旋涂/滴涂及后退火工艺构造CZT(S,Se)薄膜太阳能电池原型器件。以此为基础，加入具有1100 nm附近近红外吸收的Cu2-xS纳米晶体，形成内嵌LSPR增强型的太阳能电池器件。电学及电池效率测试表明，通过内嵌的Cu2-xS纳米晶体增强对太阳光近红外部分的吸收，所构造的CZTS太阳能电池原型器件的外量子效率由0.8%提高到了2.1%。以上研究结果对未来提高商用CIGS/CZTS薄膜太阳能电池的性能具有借鉴意义。