SnS/PbS nanocrystal heterojunction photovoltaics.

We report advances in the growth, characterization and photovoltaic properties of SnS nanocrystals, with controlled < 10 nm size, and their inclusion into a lead chalcogenide solar cell. The SnS/PbS nanocrystalline film heterojunction is shown to display a type II band alignment, in which the direction of flow of the photocurrent depends on the order of the layers and not the relative work functions of the contacts. On placing the SnS layer next to the indium tin oxide (ITO) cathode we observe a dramatic increase in V(oc) to as much as 0.45 V. Our results suggest that SnS nanocrystal films can be used in multi-junction solar cells, that a SnS/PbS heterojunction on its own shows photovoltaic behaviour, and that a SnS layer in an ITO/SnS/PbS/Al device is acting to suppress the flow of an electron injection current.