Optimization of nano-texture parameters of CdTe/CdS thin film solar cells

The thin film solar cells (TFSCs) are becoming more widely implemented due to their light weight, lower cost, and flexibility when compared to the conventional monocrystalline silicon wafer solar cells. Common materials used in the TFSCs today are amorphous silicon (a-Si) and microcrystalline silicon due to their abundance. However, these materials suffer from decreased absorption efficiency especially in the infrared range due to the sub-micron thickness of the absorber. Cadmium Telluride/Cadmium Sulfide (CdTe/CdS) is a promising candidate for TFSC material due to the near ideal, direct band gap of the CdTe, which allows it to be implemented without suffering greatly from decreased absorption efficiency. Nano-texturing is a widely researched and implemented way to increase the absorption of TFSCs. In this project, the wave optical analyses for the wavelength range of 300-1100 nm were executed using ANSYS High Frequency Structural Simulator (HFSS) to study the interaction of the geometric parameters of the nano-structures in CdS/CdTe TFSCs. A 3X3 factorial design of experiments was implemented to investigate 3 different levels of the height (H), diameter (D), and period (Pd) for a conical shaped nano-texture pattern and to study their effect on the absorption and the short circuit current (J_sc). A total of 27 different combinations were investigated. It was found that the model with H=1000 nm, D=1000 nm, and P/D=1 had the highest J_sc of 26.66 mA/cm², a 29.14 % increase from the planar control cell. In addition, it was noted that when the P/D ratio is 1, an increase in both height and diameter will increase J_sc. Finally, when the height was 200 nm, an increase in the diameter has little to no effect on J_sc. These findings are important to TFSCs manufactures to better design the nano-texturing implemented in TFSCs.