Photon-Assisted Electrochemical Construction of <0001>-n-ZnO/<111>-p-Cu2O Photovoltaic Devices with Intermediate TiO2 Layer

The Cu₂O/ZnO photovoltaic (PV) device is a realistic candidate for next generation thin film solar cell.  The conversion efficiency for the electrodeposited super-straight type PV device was lower than that for the thermally prepared substrate-type PV cell.  We developed a photon-assisted electrochemical process to construct the substrate-type PV device without the reduction of the Cu₂O.¹  Here, we show the photon-assisted electrochemical process to construct the substrate type Cu₂O/ZnO PV device with a photovoltaic performance. 

The Cu₂O layer was prepared by heteroepitaxial electrodeposition on <111>Au/Si wafer substrate in an alkaline solution containing copper acetate and lactic acid.  The ZnO layer was stacked on the Cu₂O layer by elecrodeposition in a zinc nitrate solution with light irradiation.  The PV device was fabricated by stacking the top Al electrode by evaporation.

The light irradiation was needed to grow the <0001>-ZnO layer having the columnar grain morphology and 3.3 eV bandgap energy on the Cu₂O layer without the reduction to metallic Cu.  The thickness increased with the deposition time up to 30 min and then decreased.  And the pores could be observed for the ZnO layer at the deposition time over 30　min.  The <0001>-ZnO/<111>-Cu₂O PV device showed a photovoltaic performance under AM1.5 illumination, and the performance changed depending on the deposition time, which strongly affected the structure of the resultant ZnO layer.  The best photovoltaic performance with short-circuit current density of 2.93 mAcm² could be obtained for the substrate-type <0001>-ZnO/<111>-Cu₂O PV device prepared at 30 min for the ZnO deposition.

 

Ref. 1.    B. M. Fariza, M. Izaki, et al., Thin Solid Films, 520(2012), 2261.