Investigation of light propagation in thin-film silicon solar cells by dual-probe scanning near-field optical microscopy

Energiewende Global climate change, scarcity of resources, and reservations about nuclear energy have triggered a signicant change in energy policy towards sustainability. Even the New York Times and The Economist use the German term Energiewende today to describe the ongoing transition to renewable energy [13]. Huge eorts are necessary to implement this transition. Several technologies for renewable energy are operational and are competing in terms of eciency and energy costs. In the end, the acceptance of renewable energy, depends on reasonable costs. Solar Cells Thin-lm solar cells are likely to reduce costs in comparison to crystalline solar cells as they require less energy during the production process. In the case of silicon-based thin-lm solar cells, the use of abundant and nontoxic material is an additional benet. Furthermore, less silicon is required. However, while the low layer thickness signicantly reduces the cost of production, it also reduces the capacity for light absorption. Weak absorptance has to be compensated for by advanced photon management techniques which trap the light by prolonging the light path inside the absorber layer. Various approaches for light-trapping have been developed, which use a variety of dierent physical phenomena [4]. No matter which kind of light-trapping concept is nally applied, the performance has to be evaluated using a suitable characterisation method. Characterisation Standard characterisation methods, e. g. current-voltage characteristics and quantum eciency measurements, can supply information about whether or not a solar cell equipped with a certain light-trapping concept achieves a higher eciency. Nonetheless, these methods are often restricted to macroscopic information on the entire solar cell. The internal mechanism of light guidance therefore remains unknown. A deeper understanding of the internal mechanism is, however, the basis of a targeted development and implementation of new light-trapping concepts. Simulations are one way of gaining access to microscopic information about the interaction of light with sub-wavelength structures.