Enabling Silicon for Solar-Fuel Production

Silicon is widely used for photovoltaic applications, due to its superior advantages of low cost and narrow band gap matched to the solar spectrum. It is therefore a perfect candidate for the bottom cell of a tandem design. The thermodynamic and kinetic problems of Si in aqueous solution are considered as the major issues to solve in order to apply it to photoelectrochemical solar-fuel conversion. Surface alteration techniques are important for overcoming these intrinsic drawbacks. An ideal coating should satisfy the BORSA criteria, providing a strong built-in asymmetry, proper optical modulation, minimum resistance losses, chemical stability, and high activity toward the desired reactions. Hybrid configurations, by integrating a molecular sensitized solar cell, a solid-state/quantum dots sensitized solar cell, or an organic solar cell with a Si photocathode or Si photoanode, could be one of the alternative approaches for system integration, depending on the band gap of the water oxidation and water reduction components. In addition, cost-effective fabrication processes like inkjet printing and sol-gel processing as well as screening novel electrocatalysts through compositional and structural modification have been developed and are promising paths for development. Computational screening together with a combinatorial experimental verification provides an effective way to successfully identify novel, extremely durable, and selective photocatalysts and electrocatalysts with high activities.