Analysis of quantum efficiency and optical enhancement in amorphous Sip–i–nsolar cells

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Abstract
The effect ofi‐layer thickness, tin oxide texture, and back reflector (BR) on optical enhancement has been systematically studied in a series of 20 a‐Si p–i–n solar cells. The internal quantum efficiency has been analyzed by a simple model based on the work of Schade and Smith. The enhancement of optical absorption is characterized bym, a wavelength‐dependent fitting parameter representing the increase in optical pathlength relative to thei‐layer thicknessd. Solar cells with an Al BR have negligible optical enhancement, withm < 1.5, consistent with large parasitic absorption at the Al/Si interface as reported by others. Solar cells on highly textured SnO2with ZnO/Al or ZnO/Ag BR have peak values ofm ∼ 3–4, with ZnO/Ag having slightly larger values than ZnO/Al. It was found thatmhas a strong dependence on the product αd, and that maximum values ofmincrease with reflectivity of the BR. It is shown that a major source of parasitic absorption loss at long wavelengths is light trapping in the textured SnO2front contact. Copyright © 2002 John Wiley & Sons, Ltd.