Micro- and nanotopographies for photoelectrochemical energy conversion. I: The photovoltaic mode

The development of an efficient photovoltaic electrochemical solar cell with n-Si (1 0 0) based on the nanoemitter concept is described. The corresponding structure results from the self-organized formation of nanopores in about 10 nm thick silicon oxide during photocurrent oscillations in dilute fluoride containing solutions. The oscillations occur at higher anodic potentials and, due to the stress between Si and its anodic oxide, nanopores form in the oxide. Site selective metal electrodeposition (Pt) into those pores that have contact to the Si substrate and immersion into an acidic iodine-iodide redox electrolyte gives efficiencies in the range of 10%. Model experiments on the electrodeposition of Pt nanoparticles on n-Si (1 1 1) using photoelectron spectroscopy, performed with synchrotron radiation and atomic force microscopy in the contact- and tapping mode show that upon Pt deposition, silicon oxide is formed and step-bunching is observed. Mechanistic models are presented that explain the observed features. Scanning tunnelling experiments are performed with the tip on top of Pt nanoparticles. The resulting local I–V characteristics are interpreted based on a modified MOS (metal-oxide-semiconductor) model.

► The preparation and the operation principles of photoelectrochemical nanoemitter solar cells are described. ► A solar-to-electrical conversion efficiency of >11% is reached. ► The influence of the surface electronic condition of Si electrodes on the surface chemistry is demonstrated. ► Simultaneous oxide formation and step bunching is observed upon Pt electrodeposition. ► The current-voltage behaviour in STS experiments on Pt nanoparticles is analyzed.