The Fabrication and Analysis of Bifacial Solar Cells from Dendritic Web Silicon Substrates

Abstract

Bifacial solar cells, which respond to light incident on either the front or the back surface, have been fabricated using dendritic web silicon as the substrate material. Both p‐type and n‐type substrates have been used, with resistivity ranging from 0.2 to 100 Ω‐cm for p‐type and from 0.2 to 10 Ω‐cm for n‐type. The thickness of the web substrates varied from 100 to 160 μm. The performance of the cells was found to depend strongly on substrate resistivity, with the highest resistivity giving the best results. Efficiencies in excess of 15% under front illumination, and approaching 15% under back illumination, have been measured. The efficiency under back illumination decreases dramatically with resistivity because of a decrease in minority carrier diffusion length, as deduced from measurements of internal quantum efficiency. The ratio of short‐circuit current under back illumination to short‐circuit current under front illumination also decreases with illumination level below 1 sun. The observed effects of resistivity and illumination level on cell performance are throught to be a consequence of the presence of extended defects (dislocations decorated with precipitates) in web material.