Discussion and Simulation about the Evaluation of the Emitter Series Resistance

The emitter series resistances (Rs,emi) can be extracted from experimentally measured JV curves using the two-light intensity method (TLIM) but it can also be calculated from the emitter geometry using analytical formulas and finally also computed with arbitrary precision using finite element simulation (FES). On the one hand formulas and FES consider Rs,emi as distributed, on the other hand the TLIM assumes Rs,emi not to be distributed. The derivation of formulas for a lumped Rs,emi assumes a spatially uniform current density source, which is the case in short circuit condition (Jsc), less at maximum power point (mpp) and is wrong at open circuit. We compare at mpp the results of TLIM, analytical formulas and FES for which the current density source is a 1D simulated JV curve. In the case of a low/high sheet resistance homogeneous emitter, but also for a selective emitter, these methods agree well and the impact on cell efficiency is particularly small. This is partially explained by the fact that the voltage drop and so the spatial distribution of the current density source over the emitter is small at mpp. We also clarify many issues about the various methods used and discuss the limitation of not taking into account Joule losses induced by diffusion.