A novel efficient Si-based photoelectrochemical solar cell is described that operates in the photovoltaic and photoelectrocatalytic mode. Silicon surface nanostructuring by electrochemical conditioning was used for the realization of the concept of a nanoemitter solar cell. The cell consists of a nanoporous passivating silicon dioxide mask on the silicon surface, made using a specific anodic conditioning protocol, and metallic nanoemitter islands that were deposited into the oxide nanopores. For efficient devices, a pore deepening procedure was applied. The metal nanorods act as nanoemitters for minority charge carrier collection. The photoelectrochemical solar cell n-Si / SiO2 /Pt / I-/I3- / Pt CE is stable and has efficiencies above 10%. Present limitations in solar-to-electrical conversion efficiency, due to interfacial recombination, will be addressed. The fact, that the observed open circuit voltage is large is explained by the formation of an electrolyte-metal-oxide-semiconductor junction. Due to simultaneous Si oxidation upon Pt deposition we assume an ultrathin oxide layer between the Pt nanoislands and the Si substrate. Model experiments on the electrodeposition process were performed using synchrotron radiation photoelectron spectroscopy (SRPES) to investigate surface chemistry and -electronics. The competition between valence band- and conduction band processes in the metal deposition reactions will be discussed.