Operating principles of three-terminal solar cells

Most tandem solar cells are either two-terminal devices where the subcells are electrically connected in series or four terminal devices where each subcell is operated independently. There are trade-offs between the two integration schemes in terms of ease of fabrication, overall efficiency, and spectral sensitivity. Three-terminal (3T) tandem cells can combine the best aspects of both integration schemes if designed properly. Using a 3T design based on an interdigitated back contact (IBC) Si device with conductive front surface, combined with a wider bandgap III-V top cell, we discuss the operation of three terminal tandems in detail. We present technology computer aided design (TCAD) device physics simulations to describe trends in performance. We show that this type of 3T device can provide a robust operating mechanism to efficiently capture the solar spectrum without the need to current match sub-cells or fabricate complicated metal interconnects between cells.