Current Transport Properties of CuS/Sn:In2O3 versus CuS/SnO2 Nanowires and Negative Differential Resistance in Quantum Dot Sensitized Solar Cells

The structural, optical, and electrical transport properties of nanowires obtained by the deposition of Cu over Sn doped In2O3 and SnO2 nanowires followed by processing under H2S between 100 and 500 °C have been investigated for their use in quantum dot sensitized solar cells. We find that the CuS/Sn:In2O3 nanowires obtained between 100 and 200 °C consist of hexagonal CuS and cubic In2O3 but higher temperatures lead to the formation of Cu0.23In2.59S4 nanowires. Moreover, we observed the existence of SnO2 quantum dots in tetragonal Cu2SnS3 nanowires obtained at 400–500 °C which are responsible for ultraviolet emission at 3.65 eV and a breakdown of the dipole forbidden rule in SnO2.The CuS/Sn:In2O3 nanowires obtained at lower temperatures exhibit better rectifying current–voltage characteristics and higher currents, but we did not observe negative differential resistance, as expected from a p–n tunnel junction, although this occurred by bringing Sn:In2O3 nanowires in weak contact with p-type CuS, similar to...