Monolithic integration of a p-n junction and porous silicon host matrix for next generation photovoltaics

We report on a novel three-dimensional Si p-n junction that is capable of performing photovoltaic energy conversion. Vertically aligned pores with a very high aspect ratio of ≫ 100 were formed into a p-type Si substrate through an electrochemical etching process. A conformal p-n junction was then created in the etched porous silicon region by introducing phosphorous dopants through proximity rapid thermal diffusion. Al electrodes were subsequently evaporated on the front and back sides of the diode to establish electrical contact to the n-type and p-type regions respectively. Typical device structures resulted in highly three-dimensional diodes with pores extending up to 100 μm deep into the bulk Si. Porous films this thick correspond to an effective internal surface area of ∼ 5150 cm²/cm³. This ultimately makes the device applicable to both inorganic and organic next generation photovoltaics where it is desirable to maximize the amount of interfacing surface to a given photoactive compound. Dark box and illuminated I–V measurements of the device demonstrated successful monolithic integration of a p-n diode and a high internal surface area host matrix.