Feasibility of porous silicon as a primary material in solar cells

Porous silicon was anodically etched as a function of hydrofluoric (HF) acid concentration and current density to determine the relationship between photoluminescence peak emission wavelength and the parameters of each etch condition. This was done to study the feasibility of fabricating a three-band-gap solar cell on a single wafer silicon sample. The design required that two regions of the wafer sample be etched under different conditions so that two distinct energy band gaps could be produced. One region was first anodically etched in a solution of 10% HF. That region and a second region were then anodically etched in a solution of 20% HF. The third energy band gap for the solar cell was that of native crystalline silicon. The results were characterized by photoluminescence (PL), capacitance, and current-voltage (I-V) curves obtained in the dark and under one sun illumination. Results obtained from PL showed that each etch concentration (except 15% HF) produced a characteristic peak wavelength, 5% HF created 589 nm, 10% HF created 611 nm, 20% HF created 663 nm, and 25% HF created 652 nm. Results obtained from capacitance measurements showed that porous regions between 3 and 10 nm were produced in 10 min etches. Results obtained from (I-V) curves showed non-linear behavior. Photovoltaic behavior was seen under one sun illumination with I-sc of about - 0.02 mA, V-oc of about 0.1 V and a calculated fill factor of about 0.2. (C) 1999 Elsevier Science B.V. All rights reserved.