Enhanced photoelectrochemical properties of Z-scheme ZnO/p-n Cu2O PV-PEC cells

Abstract

We have tailored a photovoltaic-photoelectrochemical (PV-PEC) cell by integrating p-n Cu2O thin films and ZnO nanorods (NRs) on conductive oxide substrates for water splitting. The combined PV-PEC cell can benefit not only from the high oxidation potential of ZnO NRs but also from the visible range light absorption of Cu2O photovoltaics. Differently from previous methods to fabricate p-n Cu2O junctions, we employed the type transition from p-to n-Cu2O by a simple solution treatment and then p-Cu2O was coated on n-Cu2O to smoothen the p-n junction interface. We for the first time produced p-n homo-junction Cu2O layers using the identical electrodeposition process. After Au thin film coating on n-Cu2O and p-n Cu2O layers by sputtering high-density ZnO NRs were grown by the hydrothermal method to construct the Z-scheme band structures. By comparing the photoresponses of ZnO NRs/Au/n-Cu2O and ZnO NRs/Au/p-n Cu2O, we could elucidate the effect of the built-in potential on PEC properties by p-n Cu2O. ZnO NRs/Au/p-n Cu2O showed the onset potential of -0.330 V which is more cathodic by 0.167 V than ZnO NRs/Au/n-Cu2O. Also, its photocurrent was 0.206 mA/cm(2) under 0.2 V vs SCE which is 237% higher than that of ZnO NRs/Au/n-Cu2O. These enhancements are attributed to the internal electric field by the p-n junction and the efficient charge separation and migration by utilizing both the p-n junction and the Z-scheme. (C) 2018 Elsevier B.V. All rights reserved.