Optical and Electrical Loss Analysis of Thin-Film Solar Cells Combining the Methods of Transfer Matrix and Finite Elements

In order to improve the power conversion efficiency of thin-film solar cells, it is essential to identify and quantify their dominant loss mechanisms and, thus, guide experimental device optimization. We provide this functionality via loss analyses determined from computer-aided modeling and numerical device simulations. Since electrical and optical effects influence each other within solar cells, the consideration of an isolated parameter is often not sufficient for maximizing cell performance. Therefore, a holistic perspective, including both the effects, is developed. Its modeling is achieved by an interplay of an optical transfer-matrix method and a quasi-3-D electrical finite-element method. Optical refractive information and electrical resistivity data have been measured experimentally and put into the model in order to forecast device $I\text{--}V$ curves. Finally, these $I\text{--}V$ curves are used to assign and quantitatively calculate the loss mechanisms of grid shading, reflection, parasitic and incomplete absorption, local maximum power point mismatches, undergrid reverse currents, and ohmic losses. We verified our approach using thin-film CuIn $_{1-x}$ Ga $_{x}$ Se $_{2}$ cells with a variable thick front contact made of aluminum-doped zinc oxide. This discussion guides laboratory work to the relevant loss mechanisms and enables to rapidly test new innovation ideas by means of numerical simulations.