Designing IBC cells with FFE: Long range effects with circuit simulation

IBC cells with Front Floating Emitter (FFE) pose different design challenges compared to more conventional IBC cells with FSF (Front Surface Field). The FFE enables hole transport over distances that are large compared to the typical BSF or emitter width. The core of the cell design is commonly a device simulation in which, because of the computer resources involved, typically one simulates an as small as possible, but representative part of the solar cell. In an IBC cell this corresponds to 1/2 of the BSF and 1/2 of the emitter. Such a unit cell does not account for important geometric features, such as busbars and pads, edges or interruptions in metallization fingers. We show how to construct an equivalent circuit for our Mercury FFE IBC cells to model features beyond the unit cell efficiently, taking into account the lateral hole transport in the FFE. We compare and calibrate the circuit model against device simulations with quokka.