InGaN/Si Double-Junction Photocathode for Unassisted Solar Water Splitting

Simultaneously achieving efficient and stable operation is a major challenge for developing sustainable and economical solar water-splitting systems. In this work, we demonstrate, for the first time, a monolithically integrated InGaN/Si double-junction photocathode, which can enable relatively efficient and stable unassisted solar water splitting. The device consists of a p-type InGaN top junction, which is monolithically integrated on a bottom Si p–n junction through a dislocation-free n ++ /p ++ InGaN nanowire tunnel junction. With the incorporation of Pt catalysts and a thin Al2O3 surface passivation layer, a solar-to-hydrogen efficiency of ∼10.3% and stable operation of 100 h was measured in 0.5 M H2SO4 in a two-electrode configuration for unbiased photoelectrochemical water splitting. Significantly, such an efficient and stable water-splitting device is achieved using the two most produced semiconductors, i.e., Si and Ga­(In)­N, promising large-scale implementation of efficient, stable, and low-cost solar hydrogen production systems.