Study Of Highly Efficient Flexible Cu?In,Ga?Se₂ Solar Cells On Stainless Steel Substrate

Cu?In,Ga?Se₂?CIGS? thin film solar cells are attractive and promising, due to high conversion efficiency, low cost and high stability, which have developed rapidly since the 1970 s. CIGS cells have a crucial advantage from the viewpoint of module fabrication in the backing such as glass, flexible metallic foils, polyimide?PI? foils, or a stainless steel sheet. Among these substrates, SS foil is commonly used because of its advantage of withstand high-temperature and low cost, matching coefficient of thermal expansion?CTE? and roll-to-roll processing enables high throughput manufacturing.In the first part, the influence of the roughness and CTE of the SS on the performance of the CIGS solar cells were investigated. It was found that the SS substrates don't significantly affect the CIGS thin films crystal structure. After the CIGS absorber deposition, the roughness of samples depends on the CIGS thin film. Analyzed with the property of the devices, the SS430 has an advantage over SS304 as the substrate of the CIGS solar cells.In the second part, the effects of T_S2 on the properties of CIGS thin films were systematically investigated. High T_S2 facilitates the grain growth and leads to larger grain size. It was found that the substrate temperature is a very important deposition parameter to adjust the GGI grading profiles and corresponding band gaps of CIGS thin films. High T_S2 leads to more Fe atoms diffusing from SS substrates into CIGS thin films, which will deteriorate the performances of the solar cells. All CIGS thin films show?112?,?220/204? and?116/312? orientations. Shoulder-like two-peak structure of?112? and?220/204? peaks in XRD spectra for CIGS thin films deposited at low T_S2 would be related to notch-like distribution of Ga content. The CIGS thin film solar cells with 9.2% conversion efficiency were obtained for the absorbers deposited at T_S2 of 500 ?C. Higher efficiency of 11.3%was achieved by further optimization.In the third part, the CIGS solar cell was optimized by the preparation of the Ni gird and MgF₂ anti-reflection layer. It was found that the solar cells get a long-term stability with the preparation of Ni gird tested after 120 hours. For the preparation of the MgF₂ anti-reflection layer and the optimization of the process, the loss of light on the surface of the solar cell decreases and the conversion efficiency of solar cell is improved by about 7%.