Unassisted Water Splitting Using Standard Silicon Solar Cells Stabilized with Copper and Bifunctional NiFe Electrocatalysts

Silicon photovoltaic cells functionalized with water-splitting electrocatalysts are promising candidates for unassisted water splitting. In these devices, the total surface of silicon solar cells is covered with electrocatalysts, causing issues with (i) stabilizing silicon solar cells in water and (ii) device efficiency due to parasitic optical absorption in electrocatalysts. We describe and validate a water-splitting device concept using a crystalline silicon solar cell where the front side is covered with an insulating Si3N5 antireflection coating. The Ag contacts, fired through the antireflection coating, are removed and subsequently substituted with NiFe layered double hydroxide (LDH) or Cu/NiFe-LDH electrocatalysts. In this device, only the site of Ag contacts, nearly 2% of the total device area, is covered by the electrocatalyst. We found that this small area of the catalyst does not limit device performance and the addition of a Cu interlayer between Si and NiFe-LDH improves device performance and stability. The unassisted water-splitting efficiency of 11.31%, measured without separating the evolved gases, is achieved using a device composed of three series-connected silicon solar cells and an NiFe-LDH/Cu/Ni-foam counter electrode in a highly alkaline electrolyte.