Charge Injection Into Electrodeposited Cu2O From Metallic Stacks and Graphene

Abstract

Cuprous oxide (Cu2O) is a promising semiconductor for photovoltaic applications owing to its direct bandgap, facile fabrication possibilities, and cost effectiveness. However, the efficiency of single photovoltaic cells employing Cu2O is limited to 3%–4% necessitating investigations into material quality and reliable interface conductivity with contact metals. In this article, we systematically investigate the charge transport efficiency between electrodeposited (ED) Cu2O thin films and commonly used metallic stack contact materials, such as Ti/Au, Cr/Au, and Pt. We further explore a large-area CVD-grown graphene monolayer as a transparent contact for Cu2O thin films. Using transfer length measurements (TLMs), we observe thermal emission characteristics with no noticeable Fermi-pinning effects using the metal combinations employed on ED Cu2O. We achieve the lowest reported contact resistivity on Cu2O thin films ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\boldsymbol {\rho }_{C}=2.15 \times 10^{-5} \Omega cm^{2}$ </tex-math></inline-formula> ) using a Ti–Au metal combination with the resistivity scaling exponentially with the barrier height on other metal stacks. In contrast, the true contact resistivity between a single monolayer of undoped graphene and a Cu2O thin film was measured to be an order of magnitude higher ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$5.526\times 10^{-4} \Omega cm^{2}$ </tex-math></inline-formula> ). Despite the higher resistance, this result indicates that further investigations into stacking multiple layers with careful doping control can make large area graphene attractive for photovoltaic applications using functional oxides.