X-ray Transient Absorption Spectroscopy for Solar Energy Research
Fundamental processes in solar energy conversion involve photon–matter interactions through light harvesting, excited state formation and subsequent transformation to convert light energy to electricity, heat and fuels. Intense pulsed X-ray sources from synchrotrons and X-ray free electrons lasers coupled with ultrafast lasers open up a new opportunity to reveal direct structural information about transient species in solar energy conversion processes, such as photocatalysts, photosensitizers and photovoltaic materials. In particular, transient oxidation states of metal centers in electron donors and catalysts can be unambiguously identified by the accompanying nuclear geometric transformations. X-ray transient absorption spectroscopy (XTA) enables molecular snapshots after the photoexcitation, which will enable molecular movies to be made and have a tremendous impact on our understanding of the coupling between the electron transfer events and structural control parameters of participating partners in solar fuel and solar electricity generation. This chapter describes XTA method developments, examples of its applications in solar energy research and the challenges and perspectives.