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Plating processes on aluminium and application to novel solar cell concepts
In this work, aluminum as contact material with low transfer resistance to p- and n-silicon is combined with the zincate process which enables plating on aluminum. In this way the excellent contact quality of aluminum and the high conductivity of plated layers are combined. Examples of application are given on two solar cell concepts. One is the both side aluminum contacted concept suitable for p-type and n-type base material. The double sided metallization approach is called DACAPO (Double sided Aluminum Contacted And Plated Overcoating) process. On p-type wafers, satisfactory results are shown for the metallization in terms of contact geometry (contact width down to 50 μm). Challenges of the approach such as laser and inkjet alignment and resist stability in aluminum etching solution, are discussed. Calculations of VOC and RC in dependence of the contact area show the potential of the DACAPO process for high efficiency solar cells. The second solar cell concept tested with zincate and plating is the IBC (interdigitated back contact) concept. Different possibilities of plating processes on both polarities are discussed in this context. Thickening the aluminum/silicon layer by plating results in an increased FF by 1.3% and consequently in higher cell efficiency up to 20.4%, even on small sized solar cells. The constructed metal stack is characterized by SEM-EDX analyses.