Junction Engineering in Si Photoanodes for Efficient Photoelectrochemical Water Splitting

Effective photovoltage generation and charge transport are crucial for a photoanode to achieve efficient photoelectrochemical water splitting. Although research in a Si/catalyst integrated photoanode has made great progress, the reported photovoltages are still far below the theoretical maximum of Si photovoltaics due to the interfacial defects induced at the Si/catalyst contact. Here, we report a junction interlayer design that enables the integration to generate high photovoltage along with high catalytic activity. Intrinsic and doped amorphous Si layers are deposited on crystalline Si to passivate surface defects and form charge extraction contacts. This passivation contact greatly increases the charge carrier lifetime by two orders of magnitude, forming the basis for high photovoltage generation. Conductive indium tin oxide is introduced to avoid direct Si/catalyst contact that causes interfacial charge recombination defects while facilitating charge transport to the catalyst. It also prevents Fermi level pinning on interfacial defects, allowing the high work function of the catalyst to further increase band bending in Si for high photovoltage generation. This photoanode exhibits a record high photovoltage of 707 mV, a low onset potential of 0.84 V versus reversible hydrogen electrode (RHE), and a photocurrent density of 38 mA cm–2 at 1.23 V versus RHE.