Light induced water splitting using multijunction thin film silicon solar cells

It has been widely recognised that fossil fuel reserves are not suffcient to cover the energy demand of our societies in the future, even if the energy utilisation would stagnate on today's level. The extent of the problem is also associated with the emission of the greenhouse gas CO$_{2}$ upon combustion of fossil fuels that can lead to unpredictable climate changes on earth. Nature's own processes of fuel generation based on biomass utilisation are considered to be not effcient enough to replenish the used resources on a short time scale. To relieve this predicament, a transition from fossil fuels to renewable energy sources is therefore imperative and unavoidable. Renewable and carbon-free energy from wind and solar radiation are the only means which can fully replace fossil fuels and are able to cover an increasing energy demand in the future. But up to now, these fluctuating energy resources lack an appropriate and effcient storage technology. Light induced water splitting, a process that mimics natural photosynthesis, provides a viable example of an ecofriendly energy concept as it converts solar energy into a storable and clean chemical fuel with a high gravimetric energy density, namely hydrogen. To be competitive with fossil fuels or hydrogen production by other means, this process must however become highly effcient and low-cost. In this regard, the utilisation of semiconductor based devices for the photoelectrochemical generation of hydrogen from water and sunlight is a promising and elegant means to store renewable energy and has been attracting considerable interest among research groups worldwide. To split water effciently into its components hydrogen and oxygen the semiconductor photoelectrode has to meet several requirements [...