2-D SPICE Simulation and Analytical Calculation of Spreading Resistance Effects in Emitter Wrap-Through Cells With Nonsquare Via-Hole Pattern

Abstract

Cell concepts that feature via-holes, like the emitter wrap-through concept, suffer from higher series resistance losses than conventional solar cells. A part of these resistance losses is due to the fact that a small size element, in this case a via-hole, has to collect the current of a wide area on the front side, which leads to the so-called spreading resistance. An analytical equation already exists which describes the spreading resistance effects that are present in these cells. This equation is an accurate description for a quadratic or hexagonal pattern of via-holes. For cells that feature an interdigitated metallization grid on the rear side, like emitter wrap-through solar cells, the arrangement is often nonsquare because the distance between two via-holes is different in the x- and y-directions. In this paper, it is shown that the existing formula is in excellent correlation with the results from simulation program with integrated circuit emphasis (SPICE) simulation if a quadratic symmetry element is chosen. The SPICE simulation is then adjusted for nonsquare symmetry elements, showing that the existing formula is not valid for these arrangements and has to be modified. The derived analytical modification is adapted to yield a better description of the spreading resistance in the emitter of such a cell structure for variable via-hole distances in the x- and y-directions. The relative deviation between the simulation results and the analytic approach is less than 15%. This enables an accurate calculation of the resistance losses of relevant technological configurations.