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Spectral response measures are particularly important for the characterization of photodetector devices operating at the wavelength 2.55 μm. For each sample elaborated in our laboratory (C.E.M.) and tested experimentally by spectral response, an appropriate theoretical model is proposed to calculate the quantum efficiency. The experimental and theoretical curves are compared by simulation to determine the parameters which are not available experimentally (diffusion length, recombination velocity at the surface, etc.). The modeling of the different devices permits to analyse the situation on the surface and in the bulk. Presented are theoretical models and results after spectral response simulation of Ga1–xInxSbn/Ga1–xInxSbp homojunction grown onto GaSbp substrate, Ga1–xInxSbp/GaSbn ternary heterojunction (x is the indium concentration), and GaSbp/Ga1–xInxAs1–ySbyp/GaSbn (y is the antimony concentration) quaternary heterojunction.

In this work we study the spectral responses of thin films solar cells of heterojunctions based on CuInSe2 and CuInS2. Four-layer structures are studied according to the n+n/pp+ model. First we consider the structure ZnO(n+)/CdS(n)/CuInS2(p)/CuInSe2(p+) where CuInS2 represent the base and CuInSe2 the substrate in this model. Secondly we consider the structure ZnO(n+)/CdS(n)/CuInSe2(p)/ CuInS2(p+), for this model CuInSe2 represent the base and CuInS2 the substrate. ZnO and CdS are used as window layers in each structure. Using the continuity equation that governs transport of carriers in semiconductor material, models for calculating spectral responses are proposed for heterojunctions type n+n/pp+ based on CuInSe2 and CuInS2. For each structure we have presented the energy band diagram based on the Anderson model [1] and determined the expression of the photocurrent. The theoretical results obtained allow to compare the performances of these two models by optimizing the different parameters of each structure (base thickness, diffusion length, recombination velocity at the interface, etc.) in order to improve the overall efficiency of the collection of carriers.

In this article, we study the influence of interface and surface recombination effects on the performance of a solar cell and on the photocurrent profile. This study is applied to chalcopyrite thin film solar cell comprising 4 active layers following the model ZnO(n + )/CdS(n)/CuInS2(p)/CuInSe2(p + ) where CuInS2 represents the base and CuInSe2 the substrate. It is based on the continuity equation of charge carriers in semiconductor material and the consideration of certain optical, geometric and electrical parameters (photon absorption coefficient, diffusion length, recombination velocity at the front and the back surface and at the interface between different layers, thicknesses of the layers, etc.). We also consider monochromatic illuminations ranging from visible to near infrared. The results obtained in two-dimensional and three-dimensional representations, show that surface and interface recombination centers can dramatically reduce the efficiency of the collection of carriers for certain wavelength ranges and that the efficiency depends on the area of photon absorption. The photons generated in the depletion area or close to this area are less affected by surface defects. The losses are related to the charge carriers which cross the interfaces to reach the depletion region and those which are generated in the vicinity of the surface because of the diffusion of the latter are towards the recombination centers.

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