The key role and advantages of molybdenum sheets in CIGS thin-film solar cells
In thin-film solar cell technology, copper indium gallium selenide (CIGS) cells have become a research hotspot in the photovoltaic field due to their high conversion efficiency, flexibility and bendability, as well as superior weak light performance. Molybdenum sheets, as the core back electrode material of CIGS batteries, have many unique advantages. Firstly, molybdenum sheets have excellent electrical conductivity and a high melting point, which can effectively collect and transport photogenerated carriers. At the same time, they can withstand the high-temperature selenization process in the preparation of CIGS cells (usually 500 to 600℃). Secondly, a low-resistance ohmic contact can be formed between the molybdenum sheet and the CIGS absorption layer, with a controllable surface roughness, which helps enhance the crystallization quality of the CIGS layer and improve the photoelectric conversion efficiency of the battery. In addition, molybdenum sheets can effectively prevent substrate impurities such as sodium (Na) from diffusing into the absorption layer, prevent selenium (Se) and sulfur (S) from reacting with the underlying material, and ensure the stability of the battery structure.
The Application and Optimization of Molybdenum Sheets in CIGS Batteries
In the preparation of CIGS batteries, the application of molybdenum foils mainly focuses on the preparation of the back electrode and the optimization of battery performance. Usually, a molybdenum layer 0.5 to 1μm thick is deposited on a glass or stainless steel flexible substrate by magnetron sputtering process as the back electrode of the battery. To enhance adhesion, a double-layer molybdenum structure (with a dense bottom layer and a loose top layer) can be adopted. By regulating the grain size and oxygen content of molybdenum, the contact resistance between it and the CIGS layer can be improved. For example, the incorporation of a small amount of oxygen (MoOx) can enhance the carrier collection efficiency and further increase the open-circuit voltage (Voc) and fill factor (FF) of the battery. However, molybdenum as a back electrode material also faces some challenges: The cost of molybdenum targets is relatively high, which affects the economy of large-scale mass production; On flexible substrates, overly thick molybdenum layers are prone to cracking, and the deposition process needs to be optimized. Furthermore, at high temperatures, molybdenum foil may form a MoSe₂ interface layer with selenium. Although this is conducive to ohmic contact, excessive amounts will lead to an increase in series resistance.
The future development trend of molybdenum sheets in CIGS batteries
Although molybdenum plays an important role in CIGS batteries, in order to further improve its performance and reduce costs, the future research directions mainly include: developing molybdenum alloys (such as Mo-Ti) to enhance mechanical properties and make them more suitable for flexible substrates; Explore the combination of ultrathin molybdenum layers with two-dimensional materials such as graphene to reduce costs and maintain electrical conductivity; Optimize the sputtering process to improve the reliability of flexible batteries. Through these improvements, molybdenum sheets are expected to play a greater role in CIGS thin-film solar cells, promoting the further development of photovoltaic technology.
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