A Single-Junction Cathodic Approach for Stable Unassisted Solar Water Splitting

Abstract

Summary Unassisted solar water splitting is one key step of artificial photosynthesis converting solar energy to chemical fuels. To date, however, there has been no demonstration of efficient and stable semiconductor photoelectrodes without extra surface protection for unassisted solar water splitting. In this work, we show that a single-junction approach of p-type In0.25Ga0.75N nanowires monolithically integrated on n-type Si wafers through an n++/p++-InGaN tunnel junction can drive relatively efficient and stable unassisted water splitting. A photocurrent density of 2.8 mA cm−2 was measured at zero bias versus a platinum counter electrode in a two-electrode configuration, leading to a solar-to-hydrogen efficiency of 3.4%. No performance degradation was observed for ∼300 h of unassisted solar water splitting without using any extra surface protection layers. Such a single-junction photocathode can be further integrated with a narrow band-gap junction, e.g., Si or GaAs, to achieve further improved efficiency for long-term stable solar water splitting.