Tailoring the CdS/CdSe/CdTe multilayer structure for optimization of photovoltaic device performance guided by mapping spectroscopic ellipsometry
Tailoring the CdS/CdSe/CdTe multilayer structure for optimization of photovoltaic device performance guided by mapping spectroscopic ellipsometry
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DOI：
10.1016/j.solmat.2020.110907
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发表时间：
2021-03-01
影响因子：
6.9
通讯作者：
Collins, Robert W.
中科院分区：
文献类型：
--
作者：
Alaani, Mohammed A. Razooqi;Koirala, Prakash;Collins, Robert W.
薄膜 CdTe 覆层太阳能电池是通过溅射法从沉积在透明导体涂层玻璃上的 CdS/CdSe 前层开始制造的。此类器件的性能对包括温度-时间曲线在内的制造细节非常敏感，这会导致 CdSe/CdTe 相互扩散并形成 CdTe1-xSex 带隙梯度吸收器。测绘光谱椭圆光度术 (M-SE) 已应用于 CdS 和 CdSe 薄膜进行过程校准，其中涉及根据有效厚度（体积/面积）与样品上的空间位置来确定沉积速率。目标是通过将电池参数与这两个有效厚度相关联来优化设备的性能。有意的厚度变化以及无意的空间不均匀性分别能够实现粗尺度和精细尺度的优化。使用这些方法，使用 13 nm CdS 和 100 nm CdSe 获得了 CdS/CdSe/CdTe 结构的最高性能太阳能电池。 CdS 厚度增加到 13 nm 以上会导致开路电压和填充因子降低，这是由于形成了 z 接近 0.5 的 CdSe1-zSz 相互扩散区域，合金的电子性能可能会受到影响。我们的结果表明，M-SE 与沉积不均匀性结合使用，可以作为复杂太阳能电池结构工艺优化的可行方法。
Thin film CdTe superstrate solar cells have been fabricated by sputtering starting from CdS/CdSe front layers deposited on transparent conductor coated glass. The performance of such devices is sensitive to the fabrication details including the temperature-time profile, which leads to CdSe/CdTe interdiffusion and formation of a CdTe1-xSex bandgap-graded absorber. Mapping spectroscopic ellipsometry (M-SE) has been applied to the CdS and CdSe thin films for process calibration, which involves determining the deposition rate in terms of effective thickness (volume/area) versus spatial position on the sample. The goal is to optimize the performance of the devices by correlating cell parameters with these two effective thicknesses. Intended variations in the thicknesses along with unintended spatial non-uniformities enable coarse and fine-scale optimization, respectively. Using these methods, the highest performance solar cells from the CdS/CdSe/CdTe structure are obtained with 13 nm CdS and 100 nm CdSe. An increase in the CdS thickness above 13 nm leads to a decrease in open-circuit voltage and fill-factor attributed to the formation of a CdSe1-zSz interdiffusion region with z approaching 0.5, where the alloy electronic properties are likely to suffer. Our results demonstrate that M-SE, exploited in conjunction with deposition non-uniformities, serve as a viable approach for process optimization of complex solar cell structures.