Coherent optical analysis of the ZnO/CdS/Cu(In,Ga)Se2 thin film solar cell

Objectives

- The Cu(In,Ga)Se2 solar cell presents a complex optical system. Modifying the structure of the solar cell changes the optical properties in a way that is difficult to predict. The first aim of the present work is therefore to establish a model system of the CIGS solar cell which allows the simulation of the optical cell properties such as transmittance, reflectance, and absorptance.
- The model system requires the optical constants n(delta) and k(delta) of each material in the cell structure as basic input parameters. The second task therefore consists in determining the optical constants of the thin film components of the CIGS solar cell.
- In the next step, the optical model is employed to quantify optical losses in the layer system of the CIGS solar cell. Besides the standard cell structure, the loss analysis will also address solar cells with reduced absorber thickness. The particular aim of the loss analysis is to identify potentials for optical optimization.
- The optical model further serves to estimate the short circuit current density of the solar cell from simulated absorption in the CdS/CIGS layers. These simulations shall predict optimized layer systems, i.e. favorable configurations of layer thicknesses and materials.
- The function of the single layers in the CIGS solar cell is of primarily electronic nature. However, each layer also constitutes part of the optical system. The aim of this work is to elucidate the influence of the individual layers on the optical cell properties. In particular, experiments that vary the thicknesses of each layer of the cell structure shall serve to clarify the impact of the specific layer on the short circuit current density of the device. The experiments further serve to test the applicability of the optical model.