Analysis of the effects caused by parameter inhomogeneity with a 2D modelling tool based on circuit simulation

In silicon solar cells many parameters may be laterally inhomogeneous, e.g. Rs, Rp and lifetime. In recent years powerful tools for imaging inhomogeneous properties have been established. Examples of measurements show that the potential distribution is a key parameter. A circuit simulation program with input options for several inhomogeneous parameter sets was developed in the European project PORTRAIT. The program is introduced and applications are demonstrated on example situations of parameter inhomogeneities: the potential distribution caused by a severe shunt, the impact of regions of low lifetime beneath the front metallisation, different lifetime distributions for a n-type solar cell with rear side emitter, the impact on the IV parameters when the two parameters lifetime and parallel resistance are inhomogeneous and the fill factor loss caused by finger interruptions. Excellent agreement of the simulated potential distribution resulting from strong shunts with Voc-PL measurements is demonstrated. The experimental observation that higher efficiencies are reached if impurities are concentrated locally instead of widely spread is confirmed. For finger interruptions a strong position dependence of these interruptions was observed.