Photovoltaic (PV) properties of porous silicon (PS) produced by a novel stain (chemical) etch solution based on fluoroboric (HBF4) acids are described for the first time. Sandwich structure devices in which semi-transparent continuous gold electrodes are deposited on stain-etched PS have been observed to show high efficiency in photocurrent under visible light exposure. Additionally, palladium (Pd) metallization of the nanoporous silicon (Si) has been performed using a new technique of electroless metal deposition (EMD). The resulting sandwich devices show effective PV results, and with the use of a nitrogen dye laser, the decay dynamics of the stain etched and electroless metal-deposited PV devices have been characterized in the dark and under room light (RL). The PV decay times are observed to be of the order of microseconds, and vary with etch duration as well as with the details of the EMD. Therefore, the metal-coated PS has great potential for application in solar cells and photodetectors, since efficient, stable and widely photoresponsive devices can be produced. The process is also more cost-effective than current technologies since there is no necessity for antireflection coatings, and there is also a reduction of device fabrication steps. (C) 2001 Elsevier Science B.V. All rights reserved.