Chaos: A new mechanism for enhancing the optical generation rate in optically thin solar cells
E. Seim, A. Kohler, R. Lukacs, M.A. Brandsrud, E.S. Marstein, E. Olsen, R. Blümel
The photogenerated current of solar cells can be enhanced by light management with surface structures. For solar cells with optically thin absorbing layers, it is especially important to take advantage of this fact through light trapping. The general idea behind light trapping is to use structures, either on the front surface or on the back, to scatter light rays to maximize their path length in the absorber. In this paper, we investigate the potential of chaotic scattering for light trapping. It is well known that the trajectories close to the invariant set of a chaotic scatterer spend a very long time inside of the scatterer before they leave. The invariant set, also called the chaotic repeller, contains all rays of infinite length that never enter or leave the region of the scatterer. If chaotic repellers exist in a system, a chaotic dynamics is present in the scatterer. As a model system, we investigate an elliptical dome structure placed on top of an optically thin absorbing film, a system inspired by the chaotic Bunimovich stadium. A classical ray-tracing program has been developed to classify the scattering dynamics and to evaluate the absorption efficiency, modeled with Beer-Lambert’s law. We find that there is a strong correlation between the enhancement of absorption efficiency and the onset of chaotic scattering in such systems. The dynamics of the systems was shown to be chaotic by their positive Lyapunov exponents and the noninteger fractal dimension of their scattering fractals.
Chaotic scattering of light rays is a feature of many types of surface-structured solar cells. Scattering structures that lead to chaotic scattering have an invariant set of infinitely long-lived trajectories. In this paper, we illustrate how concepts and methods from the field of chaos can provide valuable insights for further developments in a vastly different field: light management in optically thin solar cells.