Local Series Resistance Imaging of Silicon Solar Cells With Complex Current Paths

Next-generation highest efficiency silicon solar cells are often designed with elaborate doping and contacting structures that are sensitive to series-resistance-induced losses. Such structures exhibit complex asymmetric current paths, which present conceptual and technical challenges for spatially resolved characterization, which have thus far not been addressed and discussed. We show how series resistance imaging by luminescence can be adapted and interpreted for such complex devices using interdigitated back-contact solar cells as a prime example. Experiments that are supported by simulations for several cell geometries and base materials show that global series resistance and, thus, fill factor (FF) is governed by both electron and hole transport as a function of the resistances along their different current paths. A conductive boundary-based simulation environment for current-voltage (I-V) curves and luminescence images is used to further explain current transport physics and parameter correlations. Agreement within ±30% between series resistance derived from arithmetically averaged local values and conventional global measurements is achieved. The developed 2-D/3-D luminescence-experiment simulation environment opens the path for future accurate comparisons between other local and global characterization methods. Thus, we enable quantitative analysis of local series resistance phenomena induced by design or by production defects for complex silicon solar cells.