Highly Porous Cu2O Photocathode via Electrochemical Reconstruction of Dense Thin Films

Abstract

Nanostructured light absorbers in PEC devices offer enhanced charge carrier collection and increased active area compared to planar structures. This article describes a simple two-step electrochemical treatment to obtain such nanostructured films of Cu2O absorber layer. A dense Cu2O film is electrodeposited on FTO coated glass substrate at a potential of −0.35 V (vs Ag/AgCl). This precursor film is then subjected to voltage cycling in a potential range of −0.6 V to 0.6 V, resulting in reconstruction of the top 0.5 μm dense film to 10–30 nm thick nano-walled structure. The reason for this reconstruction is a concomitant etching of Cu2O as Cu2+ ions along with oxidation to CuO. A morphology preserving reduction of the porous CuO during the cathodic scan results in a nano-walled Cu2O. From linear sweep voltammetry of pristine Cu2O and CuO films, we find that reduction of Cu2O to Cu is a slow process in this potential range and hence, Cu-impurity is not observed up to 50 cycles. Such an approach offers production of phase pure nanostructured films comprising features as small as 10 nm without following any complex procedure. The reconstructed porous Cu2O shows > 50% enhancement in photocurrent over dense Cu2O.