Performance enhancement techniques for the front and back of nanostructured “black silicon” solar cells

Nanostructured black silicon (bSi) exhibits a broadband antireflection (AR) response due to graded-index and scattering effects, unlike traditional quarter-wavelength dielectric AR coatings. We present various techniques to improve the front- and back-surface performance of nanostructured bSi solar cells. Ammonium dihydrogen phosphate (ADP) is used for proximity doping to reduce the physical impact on the bSi nanostructures during front-surface emitter formation. An optimum concentration of 2 wt. % of ADP is found to result in a typical solar cell emitter sheet resistivity of 50 Ω / sq. Potassium hydroxide is used to etch off the highly doped region of the bSi solar cell front emitter, which results in lower surface recombination and up to a 23% increase in short wavelength (400 to 600 nm) internal quantum efficiency of the bSi solar cell. To reduce the series resistance and enhance surface passivation, forming gas anneal is employed, improving bSi cell’s overall efficiency by over 31%. By optimizing the back-surface-field formed by sputtered aluminum (Al), the backside recombination rate is reduced, improving external quantum efficiency by up to 11% in the long wavelength (>900 nm) region.