RayFlare: flexible optical modelling of solar cells

Abstract

Optical modelling is a key part of the design of solar cells, as the number of absorbed photons in the photovoltaic layer(s) fundamentally limits the current which can be generated by the cell. Some types of cell design, such as multi-junction cells (where multiple semiconductors with different bandgaps are stacked in a single structure to each absorb a different part of the solar spectrum) or ultra-thin solar cells (Hirst, 2019), require even more careful optical design. In the first case, it is generally desirable to match the current generated in each layer, requiring tuning of e.g. the bandgaps and layer thicknesses, while in the second case light-trapping structures such as gratings or surface textures are required to maintain high absorption and thus current while reducing the semiconductor thickness. Light-trapping structures range from the relatively simple (e.g. dielectric layers used as antireflection coatings on the front surface of all commercial solar cells) to highly engineered structures for very specific purposes (e.g. diffraction gratings for ultra-thin gallium arsenide (GaAs) solar cells for space applications). As such, many different simulation methods exist which are appropriate for modelling the effect of different light-trapping structures.