Operation of the Three Terminal Heterojunction Bipolar Transistor Solar Cell
The three terminal heterojunction bipolar transistor solar cell (3T‐HBTSC) is characterized by a muti‐junction solar cell structure that resembles that of a (npn or pnp) bipolar transistor. The top cell consists of the top np (pn) layers which are made of a high bandgap semiconductor. The bottom n(p) layer is made of a low bandgap semiconductor and, together with the middle p(n) layer, forms the bottom solar cell. The transistor structure allows some simplifications in the layer structure with respect to that of conventional multi‐junction solar cells since, for example, tunnel junctions are not necessary. In spite of the name, in the 3T‐HBTSC the transistor effect has to be avoided since, in the limit, this would result in the voltage of the top cell being limited by the voltage of the bottom cell.