Ultrafast probes at the interfaces of solar energy conversion materials

Ultrafast carrier dynamics at interfaces plays a major role in governing solar energy conversion efficiency in solar conversion systems, especially in solar cells and photoelectrochemical devices. In this perspective, we discuss recent advances in ultrafast spectroscopic probes to understand the dynamics at such interfaces. Transient reflectance (TR) enables monitoring of the surface carriers that are within ∼10 nm of the surface or interface of interest. Crucial parameters such as surface recombination velocity and carrier diffusion can be determined. When a strong surface or interfacial field is present the reflectance spectrum will exhibit Franz-Kelydesh oscillations. Monitoring the transient formation or decay of such oscillations informs about the interfacial field and is referred to as transient photoreflectance (TPR). Such fields are helpful in designing systems in order to move carriers away from surfaces where photocorrosion can occur and towards catalytic surfaces. Finally, we discuss transient infrared attenuated total reflection (TATR) to probe the ultrafast reaction intermediates in a photo-driven chemical reaction.