Xiao Jianling, Fang Hanlin, Su Rongbin, Li Kezheng, Song Jindong, Krauss Thomas F, Li Juntao, Martins Emiliano R
Opt Express. 2018 Mar 19;26(6):A341-A351. doi: 10.1364/OE.26.00A341.
It is now well established that light trapping is an essential element of thin film solar cell design. Numerous light trapping geometries have already been applied to thin film cells, especially to silicon-based devices. Less attention has been paid to light trapping in GaAs thin film cells, mainly because light trapping is considered less attractive due to the material's direct bandgap and the fact that GaAs suffers from strong surface recombination, which particularly affects etched nanostructures. Here, we study light trapping structures that are implemented in a high-bandgap material on the back of the GaAs active layer, thereby not perturbing the integrity of the GaAs active layer. We study photonic crystal and quasi-random nanostructures both by simulation and by experiment and find that the photonic crystal structures are superior because they exhibit fewer but stronger resonances that are better matched to the narrow wavelength range where GaAs benefits from light trapping. In fact, we show that a 1500 nm thick cell with photonic crystals achieves the same short circuit current as an unpatterned 4000 nm thick cell. These findings are significant because they afford a sizeable reduction in active layer thickness, and therefore a reduction in expensive epitaxial growth time and cost, yet without compromising performance.
现在已经充分证实，光捕获是薄膜太阳能电池设计的一个关键要素。众多光捕获几何结构已应用于薄膜电池，特别是基于硅的器件。砷化镓薄膜电池中的光捕获受到的关注较少，主要是因为由于该材料的直接带隙以及砷化镓存在严重的表面复合这一事实，光捕获被认为吸引力较小，而表面复合尤其会影响蚀刻的纳米结构。在此，我们研究在砷化镓有源层背面的高带隙材料中实现的光捕获结构，从而不会干扰砷化镓有源层的完整性。我们通过模拟和实验研究了光子晶体和准随机纳米结构，发现光子晶体结构更优，因为它们表现出更少但更强的共振，这些共振与砷化镓从光捕获中受益的窄波长范围匹配得更好。实际上，我们表明具有光子晶体的1500纳米厚的电池实现了与未图案化的4000纳米厚的电池相同的短路电流。这些发现意义重大，因为它们能够大幅减小有源层厚度，从而减少昂贵的外延生长时间和成本，同时又不影响性能。
