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FDTD simulation of light propagation inside a-Si:H structures

Pinho, P. ; Fantoni, A. F.

Materials Research Society Symposium Proceedings Vol. 1245, Nº A15-04 , pp. -- - --, January, 2010.

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We have developed a computer program based on the Finite Difference Time Domain
(FDTD) algorithm able to simulate the propagation of electromagnetic waves with wavelengths
in the range of the visible spectrum within a-Si:H p-i-n structures. Understanding of light
transmission, reflection and propagation inside semiconductor structures is crucial for
development of photovoltaic devices. Permitting 1D analysis of light propagation over time
evolution, our software produces results in well agreement with experimental values of the
absorption coefficient. It shows the light absorption process together with light reflection effects
at the incident surface as well as at the semiconductor interfaces. While the effects of surface
reflections are easily taken into account by the algorithm, light absorption represents a more
critical point, because of its non-linear dependence from conductivity. Doping density, density of
states and photoconductivity calculation are therefore crucial parameters for a correct description
of the light absorption-transmission phenomena through a light propagation model.
The results presented in this paper demonstrate that is possible to describe the effect of
the light-semiconductor interaction through the application of the FDTD model to a a-Si:H solar
cell. A more general application of the model to 2D geometries will permit the analysis of the
influence of surface and interface roughness on the device photovoltaic efficiency.