Nanophotonics for Thin films crystalline silicon Solar Cells – NATHISOL

Thin film photovoltaic solar cells are in development to improve the competitiveness of the solar energy, mainly by reducing the need for active material. The most widely used crystalline silicon, thanks to its intrinsic qualities - abundant, non-toxic compound and, after processing, of high electronic quality – suffers from the significant decrease of incident sunlight for active layers of the order of one micron thick. An optical engineering is required in order to maintain the absorption at a high level. Geometrical optics solutions based on a random texturing on the scale of several tens of microns are inadequate, and approaches consisting of diffractive structure of low index materials at the front interface are insufficient.
Recently, innovative solutions have been proposed in the frame of nanophotonics. They consist of either a periodic structure of the active layer at the scale of the wavelength, such as photonic crystals, or of an additional metal structure exhibiting plasmonic effects, also at the scale of hundreds of nanometers. These two structures generate multiple optical resonances in the active layer, contributing to an improved absorption over a wide spectral range, provided the optogeometric parameters of the structure are optimized. Two laboratories within this project, INL and LPN, have theoretically shown very significant increases of the absorption, the first group using photonic crystals, the second one using plasmonic structures. This increase was optically measured in hydrogenated amorphous silicon, prepared at LPICM and then structured at INL, in the frame of the previous ANR "SPARCS" project.
This project, involving INL, coordinator, LPN, LPICM and TOTAL, aims to conceive, fabricate and characterize advanced photovoltaic solar cells based on crystalline silicon technology.
More precisely, we will use an epitaxial crystalline silicon thin film grown by PECVD at low temperature. This material requires an additional transfer step on a substrate but it has potential higher yield than deposited microcrystalline silicon. We will thus explore the potential of both photonic crystals and plasmonic structures, since the integration enables the realization of structures of different kinds and shapes.
The project requires, in addition to the management and valorization, three main tasks: the electromagnetic and electrooptic simulations for the structural optimization, the fabrication including epitaxial layer growth, transfer, nanoimprint replication of patterns over large areas, and the accurate characterization of nanostructured materials, and the morphological, optical and electrical characterization of the fabricated cells. A specific task will address the conditions and the potential of the industrial transfer of our approaches.
The project fits very well the theme 1.3 of the "PROGELEC” call. Results will be published and presented at international and national levels, with a possible valorization of the applications. They may also be of interest for other sectors of photovoltaic and optoelectronics.