Improvements in electrodeposited Cu2O as the wide bandgap cell for a tandem solar architecture

Abstract

Paper presented to the 3rd Southern African Solar Energy Conference, South Africa, 11-13 May, 2015.Cuprous oxide is a well-known wide-bandgap material with Egap commonly reported around 2.0 eV, but with some reports ranging from 1.7eV to 2.5eV. With a bandgap around 2.0 eV it is a great candidate for the top cell of a stack tandem architecture paired with a bottom silicon cell. However the actual reported efficiencies of single junction devices are usually much lower than would be expected, probably rooted in possible defects, nonstoichiometry or microstructural flaws. We report on electrodeposited thin films and their growth modes under different conditions. Microstructural improvements have been made using seeding layers before electrodeposition; these are mainly focused on growing columnar shaped grains. Cu2O that has been electrodeposited has a flowering or dendritic microstructure. When the electrodeposition is seeded appropriately the dendrite arms from the flower no longer grow resulting in nicely faceted grains and a columnar shape. This well-crystallized columnar structure is meant to increase the hole collection length by avoiding recombination at grain boundary defects as a means of increasing the efficiency. Seeding the growth on the films has resulted in Cu2O films that are more controllable in the electrodeposition process, with a more consistent grain orientation. SEM and XRD analysis were performed to show these results.