An optical study of each layer in a-Si:H solar cells

Parasitic optical losses in amorphous silicon based solar cells were determined by evaluating the film layers as they actually exist in the device structure. The absorption coefficient, refractive index, and thickness of all the layers in the cells were calculated simultaneously using absolute spectral response and reflection measurements. A computer program fitted these measurements to the cell´s structure using semiconductor and damped harmonic oscillator models. The algorithm was based on minimization of error using a simplex method. The optical stack was treated coherently, taking into account interference effects that were evident in the spectral response and reflection spectra. Results were tested for consistency by the comparison of paired samples with slightly different structures. It was concluded that the thicknesses, absorption and dispersion of the individual layers in these solar cells could be resolved