ABSTRACT CdTe solar cells have become a competitive player in the commercial photovoltaic market competing with CIGS and Si wafers. Considerable research attention has been devoted to increasing the overall conversion efficiency of CdTe which reached 22%. Among the challenges facing this technology is the scarcity of Te. In this paper, we investigated the use of an ultra-thin CdTe layer, which would result in a substantial decrease in Te consumption by almost 90%. However, this substantial decrease in the absorber thickness must be accompanied by some embedded nano-light-trapping structures. The purpose of these nanostructures is to increase the light absorption of the UV-VIS and NIR wavelengths which leads to an increase in the generated photo-current. Also, an electron reflector layer must be added between the metallic contact and the thin absorber layer to mitigate the high recombination rate. Additionally, three different metallic contacts were explored: Au, Ag, and Al. The absorption in the CdTe layer which is responsible for the photo-generated current and the parasitic absorption in the metallic back contact, as well as the short circuit current densities, were determined and analyzed. The numerical Wave optics finite element method and the analytical transmission line theory were utilized. It was noted that these nanostructures showed a substantial increase in the absorption in the active CdTe layer in the visible and NIR range. A net increase in the short circuit current density of 36 % has been realized with the top nano-structured CdTe layer comparing to the flat reference cell with the same absorber volume. Furthermore, the Ag metallic back-contact outperforms both Al and Au and achieved the highest short circuit density and the lowest parasitic absorption. These findings would open a new route to integrate optimized and efficient light trapping nano-structures to further enhance the material utilization and the efficiency of the ultra-thin CdTe solar cells.

中文翻译：

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具有电子反射层的超薄 CdTe 太阳能电池中周期性纳米结构的光学建模

摘要 CdTe 太阳能电池已成为商业光伏市场中与 CIGS 和 Si 晶片竞争的竞争者。相当多的研究注意力已经投入到提高 CdTe 的整体转换效率上，达到 22%。这项技术面临的挑战之一是 Te 的稀缺性。在本文中，我们研究了超薄 CdTe 层的使用，这将导致 Te 消耗量显着降低近 90%。然而，吸收器厚度的这种大幅减少必须伴随着一些嵌入的纳米光捕获结构。这些纳米结构的目的是增加 UV-VIS 和 NIR 波长的光吸收，从而增加产生的光电流。还，必须在金属触点和薄吸收层之间添加电子反射层，以降低高复合率。此外，还探索了三种不同的金属触点：Au、Ag 和 Al。确定和分析了 CdTe 层中的吸收，它负责光生电流和金属背接触中的寄生吸收，以及短路电流密度。利用数值波动光学有限元方法和解析传输线理论。注意到这些纳米结构在可见光和 NIR 范围内的活性 CdTe 层中的吸收显着增加。与具有相同吸收体体积的扁平参比电池相比，顶部纳米结构的 CdTe 层实现了 36% 的短路电流密度净增加。此外，Ag 金属背接触优于 Al 和 Au，并实现了最高的短路密度和最低的寄生吸收。这些发现将为集成优化和高效的光捕获纳米结构开辟一条新途径，以进一步提高超薄 CdTe 太阳能电池的材料利用率和效率。