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Simplified front surface field formation for back contacted silicon solar cells
We investigate the formation of deep Phosphorus diffusion profiles with low surface concentrations in one single diffusion step. Such processes are suited for front surface field formation for n-type back-contact back-junction (BC- BJ) silicon solar cells or p-type silicon solar cells with alternative metallization techniques. The deposition temperature allows accurate control of the sheet resistance whereas the temperature of the in-situ oxidation strongly influences the profile-depth and surface concentration. The newly developed process leads to low dark saturation current densities well below 30 fA/cm2 on alkaline-textured surfaces and low short circuit current loss at the front side. Due to their depth and adjustable surface concentration, the obtained profiles are promising for front-surface- fields (FSF) and novel n-type emitters. A first implementation in BC-BJ solar cells with aluminum-alloyed emitter shows a good blue response of the solar cells and an improved efficiency compared to the reference process by 0.6%abs.