2, Walter Schottky Institut, Technische Universität München, Garching, , Germany
Detailed understanding of the opto-electronic properties of semiconductors and the driving forces and loss mechanisms that limit device performance is essential to the development of high efficiency solar energy conversion and storage systems. However, many photovoltaic and photoelectrochemical systems are difficult to model and only few experimental methods are available for direct characterization of dominant loss processes under relevant operating conditions. To this end, empirical extraction of the spatial collection efficiency (SCE) is an operando, analytical tool to study new materials, and devices. Defined as the fraction of charge carriers that are photogenerated at a given location that contribute to the measured current, the SCE provides a functional depth profile of the active regions in the device. By combining incident photons to current efficiency (IPCE) measurements with optical modeling, we have extracted SCE cross-sectional profiles of several materials and photoelectrochemical cells. Thus, SCE extraction provides an in depth understanding of the driving forces and limiting mechanisms in new materials with relatively simple apparatus. For example, analyzing the SCE at different operating potentials while performing different chemical reactions allows distinguishing between bulk and surface losses. By focusing on the SCE at the surface, we were able to discern between surface losses attributed to slow reaction kinetics and fast surface recombination processes through charged band states. In this contribution, we analyze the transport properties of four different phases of copper vanadate photoanodes with a wide range of copper vanadium ratios. The spatial collection efficiency analysis is used to extract the potential dependent surface reactivity and collection length. Phases with a high copper content show a relatively high collection length yet suffer from high losses induced by losses induced by D-D transitions.