In order to find new materials for solar energy to hydrogen conversion the number of pos­sible binary, ternary and quaternary elemental compositions to be evaluated is exceeding the experimental capability. On the other hand, the electrochemical and photophysical pro­perties of these materials cannot be rationally predicted. Thus, in order to evaluate as many as possible materials compositions at a quantitative level a sophisticated strategy for the preparation of ternary and quaternary thin film gradient materials libraries has to be coupled with a high-throughput photoelectrochemical characterization of the materials properties.The fabrication of materials libraries is achieved reactive co-sputtering and thermal processing followed by high-throughput XRD, EDX, SEM, thickness measurements and evaluation of the local electric conductivity. The high-throughput combinatorial photoelectrochemical characterization is performed using a specifically designed optical scanning droplet cell (OSDC). The precisely calibrated system delivers highly reproducible quantitative data from a large number of materials compositions. A variety of photoelectrochemical characteriza­tion techniques are available in the developed scanning droplet cell device allowing deter­mination of different materials properties, such as the type of the semiconductor, the photo­current on-set potential, steady-state photocurrent values at different potentials, surface re­combination rates and corrosion. Photocurrent spectroscopy allows acquisition of IPCE spectra and bandgap energy determination. Automated electrochemical impedance spec­troscopy (EIS) is integrated for studying photoelectrochemical properties. The type of con­ductivity, the flat band potential and carrier density can be extracted from Mott-Schottky plots, while Nyquist plots delivers information about charge transfer resistance and diffusio­nal limitations. Moreover, integrated miniaturized electrochemical oxygen and hydrogen sensors allow on-line detection of evolving product gases.To further understand and optimize the “hits” found in the high-throughput screening additional properties, such as grain boundary recombination and the dependence of electrocatalytic activity on grain orientation have to be evaluated. Scanning photoelectro­chemical microscopy (SPECM) was developed allowing insight into photoelectrochemical processes at the micro scale. Simultaneous measurement of local photocurrent and oxygen evolution rate as function of applied bias potential and illumination spectrum delivers valuable information about photoelectrochemical activity. 

Acknowledgement: The authors are grateful for financial support by the Deutsche Forschungsgemeinschaft in the framework of the SPP1613 (DFG SCHU/ 929 12-1, LU1175/10-1)