Boosting the photocathode performances of protected Cu2O inverse opals using photonic-crystal heterostructures

Cuprous oxide (Cu₂O) is a highly efficient p-type semiconductor photocatalytic material with the capability for visible light absorption. In this work, three-dimensional Cu₂O inverse opals with different diameters were prepared using the electrochemical deposition method. The photocathode performances were enhanced by adjusting the wavelength of photonic band gap, being co-modified by Au and Ag nanoparticles, applying the protective layers, and fabricating a photonic-crystal heterostructure with another p-type semiconductor. The slow-light effect leads a 23.9 % increase in photocurrent density. The co-modification of Au and Ag nanoparticles achieves a 77 % average increase in photocurrent density compared with pure Cu₂O inverse opals. Conformal protective layers, consisting of ZnO and Al₂O₃ and deposited using atomic layer deposition, prevent the photocorrosion of the Cu₂O photocathode while preserving its photocatalytic activity. After one hour of illumination, the photo-generated current density of protected Cu₂O inverse opals is nearly three times higher than that of their uncoated counterparts. By fabricating Ag-doped ZnO with p-type characteristics and combining it with Cu₂O into a heterostructure, the saturated photocurrent density of the Ag-doped ZnO/Cu₂O heterostructure reaches −3.78 mA/cm², which is almost 3.2 times higher than that of pristine Cu₂O inverse opal at −0.12 V vs RHE.