A Simple Physical Model for Three-Terminal Tandem Cell Operation
Paul Stradins, Adele Tamboli, Emily Warren
National Renewable Energy Laboratory, Golden, CO, United States

 We present a simple physical model that explains the device operation of a 3-terminal (3T) tandem on 3-terminal IBC Si bottom cell platform. If the IBC cell has two p-n and one high-low (back-surface field, BSF) junctions, the two p-n junctions strongly interact via minority carrier diffusive current through the base. In the two BSF and one p-n junction IBC platform, the BSF terminals interact via ohmic majority current in the base. This interaction considerably widens the “generating” power island in the 2D terminal current J1Jand terminal voltage V1Vplanes, governed by the balance between the generated and dissipated power in the 3T cell. The area and shape of these power islands is determined by dissipative losses in the wafer base and in the cell contacts. Both positive and negative terminal currents are allowed for 3T operation, thus allowing both the top and bottom cells operate at their full light currents, leading to new possibilities for 3T in the modules.