Enhancing solar cell efficiency by lenses on the nano- and microscale

Abstract

Metallic nanoparticles exhibiting plasmonic effects as well as dielectric nanoparticles coupling the light into resonant modes have both shown successful application to photovoltaics. On the larger scale, microconcentrator optics promise to enhance solar cell efficiency and reduce material consumption. Here we want to make the link between concentrators on the nano- and on the microscale. From metallic nanospheres we turn to dielectric ones and then look at increasing radii to approach concentrator optics on the mircoscale. The nano- and microlenses are investigated with respect to their interaction with light using 3D simulations with the finite element method. Resulting maps of local electric field distributions reveal the focusing behavior of the dielectric spheres. For larger lens sizes, ray tracing calculations can be applied which give ray distributions in agreement with areas of high electric field intensities. Calculations of back focal lengths using ray tracing coincide with results from geometrical optics simulations. They give us insight into how the focal length can be tuned as a function of particle size, but also depending on the substrate refractive index and the shape of the microlens. Turning from spherical to segment-shaped lenses allows us to approach the realistic case of microconcentrator optics and to draw conclusions about focus tuning and system design. Despite the similarities of focusing behavior we find for the nano- and the microlenses, the integration into solar cells needs to be carefully adjusted, depending on the ambition of material saving, concentration level, focal distance and lens size, all being closely related. © (2014) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.