Plasmonic enhanced solar cells: Summary of possible strategies and recent results

Plasmonic structures for light manipulation at sub-wavelength scale have received great interest in the field of photovoltaic (PV) solar cells for their potential to significantly enhance the cell's efficiency. The performance of any solar cell is determined by the capability to absorb incoming light and produce electric charges, which, in turn, has a number of limiting factors. One is related to the ever-reducing size and acceptance angle of the active region. Another is the limited spectral sensitivity of the active material, which cannot make use of significant parts of the solar spectrum. Correspondingly, the energy harvesting may be improved in two ways, namely by adopting light trapping schemes and by exploiting spectral modification processes to shift frequencies of the solar spectrum, which are initially not absorbed, into the region of maximum absorption of the cell. Plasmonic nanoparticles (NPs) can give a significant boost to both these aspects, by scattering and concentrating the electromagnetic field into the active region of the device, and by doing that within specific spectral regions, which can be properly tuned by optimizing the size, shape, distribution of the plasmonic NPs, and by choosing the right surrounding medium. During the last ten years, many papers have been published on very specific issues, but also on general properties of plasmonics applied to solar cells, with a strong increase between 2006 and 2012, followed by a period of significant, but stable, literature productivity. Given these premises, an organized and schematic summary of the main strategies and of the recent results on the field is given in this review, where different plasmonic approaches are compared and discussed, also by recalling specific examples from the literature and providing a few key conclusions to understand the main aspects and the future perspectives of the field.