What is the best strategy for light-trapping in ultrathin solar cells?

Stéphane Collin1,2

1Centre de Nanosciences et de Nanotechnologies (CNRS, Université Paris-Saclay)

2Institut Photovoltaïque d'Ile-de-France (IPVF)

"Reducing the thickness of solar cells without compromising performance is an important route towards material, energy, and cost savings. Efficient light absorption and hence high power conversion efficiency could be maintained in ultrathin absorbers using light-trapping structures that enhance the optical path, but the best strategy to trap sunlight in a solar cell is still under debate. In this contribution, we present a universal model for broadband absorption, resulting in new upper bounds for light-trapping in solar cells. Our theoretical framework is based on the description of multiple overlapping resonances in the frequency domain. It has a very broad domain of validity, encompassing and extending the whole scope of previous theories, including isotropic scattering induced by random texturing and multi-resonant effects induced by periodic nanopatterning. We also discuss state-of-the-art ultrathin solar cells. The theoretical upper bounds are compared with the best experimental and numerical results published in the literature, and shed a new light on the room for further improvements. We will discuss challenges and prospects for ultrathin single-junction and multi-junction solar cells."