The fabrication of solar cells is a multi-stage process giving rise to a multitude of combinations of materials and cell parameters such as thickness, thin film growth conditions, ordering of layers and tandem cells. Experimentally investigating these combinations to optimize cell performance is expensive and time consuming. Computer simulations of the optical and electrical functions allow for eliminating large class of ineffective combinations and containing the parameter space significantly. We modeled solar cell as a stack of layers. The wavelength dependent dielectric permittivity function defines the capacity of a material to absorb, reflect and transmit incident light. The light travels from one medium to another following simple principles and laws of reflection and refraction. Three important phenomena namely reflection, absorption and transmission take place at the interface of two layers in the cell structure. A coherent treatment of these phenomena using the incoming and outgoing and reflected electric field in each layer can be done. This approach yields the electric field at any point in each layer thereby helping in calculating the absorbed photons in the layer eventually allowing us to calculate the quantum efficiency (Q.E) and overall reflectance (R) and transmittance (T) of the solar cell. The Q.E. allows the calculation of the short circuit current generated by the solar cell and the R and T allow for the calculation of the reflection loss of the solar cell. The analytical tool used in this thesis is based on such an approach and is used to evaluate the compatibility of the different materials with each other for being used in the solar cell. We used different combinations of Transparent Conductive Oxides (TCOs’) for the solar cells analyzed in the work. The major focus of the thesis is to evaluate the dependence of the optical performance of the solar cell on the thickness of the layers of the solar cell along with different TCOs’. The solar cells considered in the work are Copper-Indium-Diselenide (CuInSe2) and Copper-Indium-Gallium-Diselenide (CIGS, CuInGaSe2). The analysis of CuInSe2 and CuInGaSe2 showed that maximum current is produced when Indium – doped tin oxide (ITO) is used as TCO. The use of ITO as TCO results in highest short circuit current density for both the structures. The combination of Zinc Oxide (ZnO) and Aluminium-doped-Zinc Oxide (ZnO:Al) leads to lowest short circuit current density and highest reflection loss. The use of CuInSe2 produces a high current compared to CuInGaSe2.
Engineering, Physics, Optical Modeling, Solar Cells, Cu(In, Ga)Se2 (CIGS), CuInSe2 (CIS)
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