Photoactive nanostructure device by electrochemical processing of silicon

The realization of a photoactive Si-based device that operates in the photovoltaic as well as in the photoelectrocatalytic mode is described. The system is based on self organized nanopore formation in the anodic silicon oxide which is present during current oscillations in fluoride containing electrolytes. Electrodeposition of Schottky barrier and/or catalytic metals into the pores forms nanoemitter contacts. In contact with redox electrolytes, comparably efficient photoelectrochemical solar energy conversion is obtained. With n-type Si, solar-to-electricity conversion efficiencies are between 6% and 7%. For illuminated p-Si, hydrogen evolution is observed. Present limitations in efficiencies are attributed to the non-optimized pore metallization process and reduced interface electronic quality for the photovoltaic system. For p-Si, the low contact potential difference between its Fermi level and the electrochemical potential for hydrogen evolution limits the attainable photovoltage. Routes for improvement of both devices are outlined.