Microstructure analysis of the epitaxial growth of cu₂o on gold nano-Islands

Cuprous oxide is a well-known wide-bandgap material with E_gap commonly reported around 2.0 eV, but with some reports ranging from 1.7eV to 2.5eV. With this bandgap it is a great candidate for the top cell of a stack-tandem solar cell architecture paired with silicon. However, the actual reported efficiencies of single junction Cu₂O 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 and making doped electrodeposited layers. Cu₂O that has been electrodeposited has a flowering/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 by avoiding recombination at grain boundary defects as a means of increasing the efficiency. SEM and TEM were used to verify the growth of the grains and the epitaxial relationship between the gold nanoislands and the Cu₂O.