A computer simulation model of amorphous silicon solar cells using a Scharfetter and Gummel solution of Poisson’s equation and Taylor and Simmons occupancy statistics for the dangling bond gap states (D states), has been developed. With a suitable choice of parameters, the numerical results for solar cell collection efficiency and dark and illuminated I-V characteristics agree well with experimental values. The model has been used specifically to study the influence of interface states at the TCO-p (transparent conductive oxide), p-i, i-n, and n-metal interfaces and to explain the beneficial role of a graded-band-gap layer at the p-i interface.

The optical properties of CuInSe2 thin films and single crystals are reported. The wavelength dependence of the refractive index and extinction coefficient is measured using multiple angle-of-incidence ellipsometry. Absorption coefficients as high as 6×105/cm are reported—the highest for any semiconductor. CuInSe2 is confirmed to have a room temperature, direct-bandgap transition near 0.96 eV for the single crystals, and 1.02 for the thin films. The difference is proposed to be due to nonuniformity in composition of the polycrystalline material. Additional absorption in the low absorption-coefficient regime is likely due to transitions associated with phonon absorptions for the single crystals. The effects of heat treatments in Ar, N, and O are shown to improve the optical properties of the thin films due to improvement in film compositional uniformity. Heating in high vacuum causes Se desorption near the film surface, causing a related degradation in the absorption characteristics.

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