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Published February 2017 | Supplemental Material
Journal Article Open

Polycrystalline Cu_(2)O photovoltaic devices incorporating Zn(O,S) window layers


The tunability of the Zn(O,S) conduction band edge makes it an ideal, earth-abundant heterojunction partner for Cu_(2)O, whose low electron affinity has limited photovoltaic performance with most other heterojunction candidates. However, to date Cu_(2)O/Zn(O,S) solar cells have exhibited photocurrents well below the entitled short-circuit current in the detailed balance limit. In this work, we examine the sources of photocurrent loss in Cu_(2)O/Zn(O,S) solar cells fabricated by sputter deposition of Zn(O,S) on polycrystalline Cu_(2)O substrates grown by thermal oxidation of Cu foils. X-ray photoelectron spectra reveal that Zn(O,S) deposited at room temperature leads to a thin layer of ZnSO_4 at the Zn(O,S)/Cu_(2)O interface that impedes current collection and limits the short circuit current density to 2 mA/cm^2. Deposition of Zn(O,S) at elevated temperatures decreases the presence of interfacial ZnSO_4 and therefore the barrier to photocurrent collection. Optimal photovoltaic performance is achieved at a Zn(O,S) deposition temperature of 100°C, which enables an increase in the short circuit current density to 5 mA/cm^2, although a small ZnSO_4 layer is still present. Deposition at temperatures above 100°C leads to a reduction in photovoltaic performance. Spectral response measurements indicate the presence of a barrier to photocurrent and exhibit a strong dependence on voltage and light bias, likely due to the photodoping of Zn(O,S) layer.

Additional Information

© 2016 Elsevier. Received 21 July 2016; revised 14 October 2016; accepted 29 October 2016; available online 6 November 2016. The authors gratefully acknowledge support from the Dow Chemical Company under the earth-abundant semiconductor project. This material is based upon work supported in part by the National Science Foundation (NSF) and the Department of Energy (DOE) under NSF CA No. EEC-1041895. Any opinions, findings and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect those of NSF or DOE. S.T.O. and A.M.S. acknowledge support from the Joint Center for Artificial Photosynthesis, a DOE Energy Innovation Hub, supported through the Office of Science of the U.S. Department of Energy under Award no. DE-SC0004993. XPS data were collected at the Molecular Materials Research Center of the Beckman Institute of the California Institute of Technology. The authors thank Carol Garland at the Caltech Materials Science TEM facility for training and guidance.

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