title: Ultrathin Epitaxial Silicon Solar Cells with Inverted Nanopyramid Arrays for Efficient Light Trapping.
abstract: Ultrathin c-Si solar cells have the potential to drastically reduce costs by saving raw material while maintaining good efficiencies thanks to the excellent quality of monocrystalline silicon. However, efficient light trapping strategies must be implemented to achieve high short-circuit currents. We report on the fabrication of both planar and patterned ultrathin c-Si solar cells on glass using low temperature (T < 275 °C), low-cost, and scalable techniques. Epitaxial c-Si layers are grown by PECVD at 160 °C and transferred on a glass substrate by anodic bonding and mechanical cleavage. A silver back mirror is combined with a front texturation based on an inverted nanopyramid array fabricated by nanoimprint lithography and wet etching. We demonstrate a short-circuit current density of 25.3 mA/cm(2) for an equivalent thickness of only 2.75 μm. External quantum efficiency (EQE) measurements are in very good agreement with FDTD simulations. We infer an optical path enhancement of 10 in the long wavelength range. A simple propagation model reveals that the low photon escape probability of 25% is the key factor in the light trapping mechanism. The main limitations of our current technology and the potential efficiencies achievable with contact optimization are discussed.
authors.affiliation: Centre de Nanosciences et de Nanotechnologies, CNRS, University Paris Sud, Université Paris-Saclay , C2N-Marcoussis, 91460 Marcoussis, France.
authors.forename: Alexandre
authors.initials: A
authors.lastname: Gaucher
authors.affiliation: Centre de Nanosciences et de Nanotechnologies, CNRS, University Paris Sud, Université Paris-Saclay , C2N-Marcoussis, 91460 Marcoussis, France.
authors.forename: Andrea
authors.initials: A
authors.lastname: Cattoni
authors.affiliation: Centre de Nanosciences et de Nanotechnologies, CNRS, University Paris Sud, Université Paris-Saclay , C2N-Marcoussis, 91460 Marcoussis, France.
authors.forename: Christophe
authors.initials: C
authors.lastname: Dupuis
authors.affiliation: LPICM, CNRS, Ecole Polytechnique, University Paris-Saclay , 91128 Palaiseau, France.
authors.forename: Wanghua
authors.initials: W
authors.lastname: Chen
authors.affiliation: LPICM, CNRS, Ecole Polytechnique, University Paris-Saclay , 91128 Palaiseau, France.
authors.forename: Romain
authors.initials: R
authors.lastname: Cariou
authors.affiliation: LPICM, CNRS, Ecole Polytechnique, University Paris-Saclay , 91128 Palaiseau, France.
authors.forename: Martin
authors.initials: M
authors.lastname: Foldyna
authors.affiliation: Institut des Nanotechnologies de Lyon (INL), Université de Lyon , UMR5270, CNRS-INSA-ECL-UCBL, Ecole Centrale de Lyon, Ecully 69134, France.
authors.forename: Loı̈c
authors.initials: L
authors.lastname: Lalouat
authors.affiliation: Institut des Nanotechnologies de Lyon (INL), Université de Lyon , UMR5270, CNRS-INSA-ECL-UCBL, Ecole Centrale de Lyon, Ecully 69134, France.
authors.forename: Emmanuel
authors.initials: E
authors.lastname: Drouard
authors.affiliation: Institut des Nanotechnologies de Lyon (INL), Université de Lyon , UMR5270, CNRS-INSA-ECL-UCBL, Ecole Centrale de Lyon, Ecully 69134, France.
authors.forename: Christian
authors.initials: C
authors.lastname: Seassal
authors.affiliation: LPICM, CNRS, Ecole Polytechnique, University Paris-Saclay , 91128 Palaiseau, France.
authors.forename: Pere
authors.initials: P
authors.lastname: Roca I Cabarrocas
authors.affiliation: Centre de Nanosciences et de Nanotechnologies, CNRS, University Paris Sud, Université Paris-Saclay , C2N-Marcoussis, 91460 Marcoussis, France.
authors.forename: Stéphane
authors.initials: S
authors.lastname: Collin
keywords: crystalline silicon; light trapping; low-temperature epitaxy; nanoimprint lithography; solar cells