Design study of a nanowire three-terminal heterojunction bipolar transistor solar cell

We present an optical design study on a nanowire heterojunction bipolar transistor solar cell. The simple structure of this novel architecture of double-junction solar cell, allows for independent power extraction from the two junctions and makes the nanowire growth easier than in current-matched double-junction solar cells as there is no need for tunnel junctions and only three main semiconductor regions must be grown. We show that the nanowire heterojunction bipolar transistor solar cell design results in an optical performance similar to comparable planar devices, with the nanowires only covering 1/3 of the substrate area. Furthermore, it allows for the growth of lattice-mismatched semiconductor combinations, which increases the detailed balance efficiency limit.