Development and characterization of photovoltaic tandem-junction nanowires using electron-beam-induced current measurements

Nanowires have many interesting properties that are of advantage for solar cells, such as the epitaxial combination of lattice-mismatched materials without plastic deformation. This could be utilized for the synthesis of axial tandem-junction nanowire solar cells with high efficiency at low material cost. Electron-beam-induced current measurements have been used to optimize the performance of single-junction nanowire solar cells. Here, we use electron-beam-induced current measurements to break the barrier to photovoltaic tandem-junction nanowires. In particular, we identify and subsequently prevent the occurrence of a parasitic junction when combining an InP n–i–p junction with a tunnel diode. Furthermore, we demonstrate how to use optical and electrical biases to individually measure the electron-beam-induced current of both sub-cells of photovoltaic tandem-junction nanowires. We show that with an applied voltage in forward direction, all junctions can be analyzed simultaneously. The development of this characterization technique enables further optimization of tandem-junction nanowire solar cells.