Question

Surface Recombination: Suppose I have a sample of 10 μm thick silicon illuminated under 775 nm wavelength light (absorption coefficient 10' cm) at an intensity of 50 mW/cm2. The surface recombination velocity and bulk minority carrier lifetime are 10 em/s (for both respectively. Assume Δη and Δp are » no or po- surfaces) and 10 us, Why is surface recombination referred as a velocity? What is the estimated short circuit current assuming no bulk or surface recombination and perfect transmittance (ie no reflection) of light at the solar cell-air interface and a perfectly reflective back contact? Calculate the quantum efficiency at that wavelength taking into account surface recombination and bulk carrier lifetimes. (Hint: determine generation rate from light absorbed travelling to the back contact and reflected back to the front face separately) a) b) e)

Answer 1

(a) The outer shell electrons remain unpaired, as a result of which voids are created on and inside the surfaces or known as "dangle" bonds. Recombination of electron-hole takes place between conduction and Valence Band on the surfaces. Large number of minority charge carriers are created which are basically referred as "surface recombination velocity".⅝