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Published November 1, 2014 | Published
Journal Article Open

Interface stoichiometry control to improve device voltage and modify band alignment in ZnO/Cu_2O heterojunction solar cells


The interface stoichiometry of cuprous oxide (Cu_2O) was controlled by adjusting the O_2 and Zn partial pressures during ZnO sputter deposition and measured by high-resolution X-ray photoelectron spectroscopy of ultrathin (<3 nm) ZnO films on Cu_2O. Open-circuit voltage measurements for ZnO/Cu_2O heterojunctions under AM1.5 illumination were measured and it was found that a stoichiometric interface can achieve the voltage entitlement dictated by the band alignment, whereas the non-stoichiometric interface showed large open-circuit voltage deficits. These results highlight not only the need for stoichiometric interfaces in Cu_2O devices, but also a reproducible experimental method for achieving stoichiometric interfaces that could be applied to any potential heterojunction partner. Additionally, valence-band offset measurements indicated changing the interface stoichiometry shifted the band alignment between Cu_2O and ZnO, which accounts for the variation in previously reported band offset values.

Additional Information

© 2014 The Royal Society of Chemistry. Received 25 Jun 2014, Accepted 28 Aug 2014; First published online 05 Sep 2014. XPS data were collected at the Molecular Materials Research Center of the Beckman Institute of the California Institute of Technology. The authors would like to acknowledge The DOW Chemical Company for funding and collaborating in this work.

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