Tailoring phase and oxidation states of Cu by varying oxygen gas flow rates in rf sputter deposition for photovoltaic devices

摘要

Cuprous oxide (Cu_2O) is a natural p-type semiconductor with a direct bandgap of ~2eV [1-3] with high optical transparency in the visible region, non-toxicity, and low cost for mass production. In addition, Cu_2O thin films have high exciton recombination energy and theoretical power conversion efficiency of 20%, making them potentially useful in optical photovoltaic devices such as inorganic solar cells [4-6], organic solar cells (OSCs) [7-9] and organic light emitting devices (OLEDs). Although Cu_2O offers great advantages in application, the difficulty of growing single phase Cu_2O without cupric oxide (CuO) contamination still remains. Various deposition methods for the formation of Cu_2O have been attempted such as thermal and chemical oxidation [10,11], electrodeposition, and sputter deposition [12,13]. Among those techniques, sputter deposition holds the greatest promise of controlling the ratio of cupric to cuprous oxide in copper oxide films.