面向超薄晶硅太阳电池的无序化调制二维纳米光子晶体陷光特性研究

Nanophotonic-crystals (NCs) light-trapping which was developed recently is a promising technique for efficient light absorptions and conversions. Recent reports show that disordered-structures can be introduced into perfect periodic NCs to further improve the overall light-trapping performance, especially on broad -band and on wide-angle. In order to achieve highly efficient light-trapping on sub-10 μm crystalline silicon (c-Si) flake, this proposal is provided to study the effects of disorders, including local defects, symmetries-destroys, periodic-randomizations, etc., on the light absorptions of c-Si NCs. The absorption properties related to individual disorders are first investigated in details by theoretically and experimentally, to evaluate the relations between local disordered-structures and the efficiencies of light-trapping. Absorptions from periodic, quasi-periodic, quasi-random NCs are employed to study the dependences of light-trapping on the wave lengths and incident angles, which can help to understand the coherent and localization properties, respectively, related to periodical and disordered structures. Combine the concept of impedance matching with disordered-NCs, highly efficient broad-band (and wide-angle) light-trapping in thin c-Si film that approaching the theoretical (Lambertian) limit will be achieved. The successful implementation of this proposal may help to provide theoretical and technical supporting toward high efficiency and cost-effective c-Si thin film solar cells.

纳米光子晶体陷光是近年来发展起来的具有广泛应用前景的新型光能高效吸收和转化技术。近期研究发现在光子晶体阵列中引入无序化结构调制有助于在宽带、广角范围内进一步提升陷光效果。本项目基于10 μm厚度超薄晶硅高效光利用目的，以硅基二维纳米光子晶体为研究对象，结合实验和数值模拟详细考察局部缺陷、晶胞对称性破缺、周期结构随机化等无序化调制对光子晶体光吸收的影响，探讨无序化结构对电场能量分布和陷光效率的作用机制；通过对比研究周期、准周期、准随机等结构陷光效果与入射光波长和角度的依赖关系，理解与无序化相关的宽带、广角陷光机制；进一步通过结构设计和制备技术研究，在高效无序化调制纳米光子晶体中引入具有出色阻抗匹配特性的光学结构，探索突破吸收极限的途径。本项目的成功实施有望为面向下一代高性能超薄晶硅太阳电池的效率提升和成本降低提供理论和技术方面的支撑。

超薄晶硅电池在有效降低材料成本的同时，在柔性光伏器件等领域也展现出广泛应用价值和前景。但是随着硅片吸收层厚度降低，衬底对入射光的吸收能力也随之减弱，导致电池性能达不到预期。纳米二维光子晶体通过特殊的耦合方式，实现对入射光的有效调控，在薄硅上展现出较好的陷光特性。本项目通过实验和数值模拟相结合的方式，考察了几种二维光子晶体陷光结构，具体的结果和结论如下：1）在20μm厚度薄硅的正反两面分别针对短波和长波陷光，制备出双面微纳米倒金字塔周期阵列结构，光电流密度高达39.86 mA/cm2；2）采用原位金属催化腐蚀技术，重构纳米锥/纳米柱二元结构，在深度仅仅1.5μm的绒面下，结构在400-800 nm波段的反射率低至1.5%；3）采用一步法金属催化腐蚀在多晶硅表面制备出高效陷光绒面，帮助黑硅电池效率由17.8%提高到18.3%，具有直接的推广价值。这些先进陷光结构设计，对推动超薄晶硅太阳电池领域的发展起到关键作用，有助于加速光伏制造成本的大幅降低。