Silicon nanowire solar cells: from nanostructures to devices Martin Foldyna LPICM-CNRS, Ecole Polytechnique, Université Paris-Saclay, 91128 Palaiseau, France martin.foldyna@polytechnique.edu CEITEC 2017, April 27, Brno, Czech Republic martin.foldyna@polytechnique.edu

From atoms and molecules to devices LPICM research teams 30 countries 120 people From atoms and molecules to devices Nanostructured silicon: thin films and applications PECVD silicon material (Thin films & nanowires) Thin film solar cells Molecular dynamic, physical modeling Organic & Large Area Electronics Flexible electronic for sensor and energy OPV & hybrid solar cells, OLED for lighting Compact modeling of organic electronics Nanomaterial & Nanodevices Carbon nanotubes et graphene synthesis Organization & integration of nano-objects Nanodevices for electronics, sensors and field emission Optical nano-characterization Polarimetric instrumentation Metrology for microelectronics Biomedical apllications Nano-Raman IFSTTAR: Institut Français des Sciences et Technologies des Transports, de l’Aménagement et des Réseaux (LCPC + INRETS)

Outline Motivation Fabrication of nanowires and radial junction devices Solar cells based on plasma enhanced VLS grown nanowires Future prospects of NW solar cell research Conclusions CEITEC 2017, April 27, Brno, Czech Republic martin.foldyna@polytechnique.edu

Why nanowire solar cells? Planar junctions on textured substrates Radial junctions Substrate I P electron hole Substrate I N P 250 nm N N 1-2 µm 100 nm Advantages of using radial junction: Light trapping effect Decouples light absorption and carrier collection Reduces light-induced degradation B.M. Kayes et al., J. Appl. Phys. 97, 114302 (2005); E. Garnett and P. Yang, Nano Letters 10, 1082 (2010). CEITEC 2017, April 27, Brno, Czech Republic martin.foldyna@polytechnique.edu

Plasma enhanced VLS Si nanowire growth Silicon NW growth Plasma enhanced chemical vapor deposition Low-temperature growth using low-melting point metals (Sn: 232 ˚C) Low cost thin film technology used in industry Fabrication possible in one-pump-down process Silicon nanowire solar cell fabrication process Metal droplet preparation Nanowire growth Radial junction formation Device finalization CEITEC 2017, April 27, Brno, Czech Republic martin.foldyna@polytechnique.edu

Plasma enhanced vapor-liquid-solid growth CEITEC 2017, April 27, Brno, Czech Republic martin.foldyna@polytechnique.edu

Bottom-up solar cell fabrication CEITEC 2017, April 27, Brno, Czech Republic martin.foldyna@polytechnique.edu

Cross-section of single radial junction Cross-section position DSi NWs core = 15 nm, 120 nm thick a-Si:H layer FIB image: courtesy of Ileana Florea CEITEC 2017, April 27, Brno, Czech Republic martin.foldyna@polytechnique.edu

Radial junction solar cells 2 µm Radial junction with ITO top contact 1 cm The radial junction density is over 5x108/cm2. S. Misra, L. Yu, M. Foldyna, P. Roca i Cabarrocas, Solar Energy Materials and Solar Cells, 118, 90-95 (2013)  CEITEC 2017, April 27, Brno, Czech Republic martin.foldyna@polytechnique.edu

Measurements at nanoscale Conductive AFM Local conductivity (topological mapping) L. Yu, L. Rigutti, M. Tchernycheva, S. Misra, M. Foldyna, G. Picardi, P. Roca i Cabarrocas, Nanotechnology 24, 275401 (2013). A. Fejfar, M. Hyvl, M. Ledinsky, A. Vetushka, J. Stuchlik, J. Kocka, S. Misra, B. O’Donnell, M. Foldyna, L. Yu, P. Roca i Cabarrocas, Solar Energy Materials and Solar Cells 119, 228 (2013). CEITEC 2017, April 27, Brno, Czech Republic martin.foldyna@polytechnique.edu

Impact of density on performance L. Yu, B. O'Donnell, M. Foldyna and P. Roca i Cabarrocas, Nanotechnology 23, 194011 (2012). CEITEC 2017, April 27, Brno, Czech Republic martin.foldyna@polytechnique.edu

Improving energy conversion efficiency CEITEC 2017, April 27, Brno, Czech Republic martin.foldyna@polytechnique.edu

History of gradual rise of cell efficiencies S. Misra, L. Yu, W. Chen, M. Foldyna, P. Roca i Cabarrocas, Review article, Journal of Physics D: Applied Physics, (2014), 47, 393001-21 CEITEC 2017, April 27, Brno, Czech Republic martin.foldyna@polytechnique.edu

Conclusions NW solar cells have very good light trapping properties High tolerance of the optical performance to structural defects Cost efficient fabrication by plasma-enhanced VLS High efficiency demonstrated even for 100 nm thick absorber Compatible with existing technologies as well as the high performance requirements (tandems) CEITEC 2017, April 27, Brno, Czech Republic martin.foldyna@polytechnique.edu

PhD candidates (some of them doctors already) LPICM Nanowire for PV team Research staff Martin Foldyna Pere Roca i Cabarrocas Jean-Luc Maurice Ileana Florea Wanghua Chen PhD candidates (some of them doctors already) Soumyadeep Misra Alienor S. Togonal Jian Tang Zuzana Mrazkova Mutaz Al-Ghzaiwat CEITEC 2017, April 27, Brno, Czech Republic martin.foldyna@polytechnique.edu

Thank you for your attention. Great thanks to Members of nanowire group at LPICM, Ecole Polytechnique Colleagues from Czech Academy of Sciences Colleagues from IEF, Université Paris-Sud Funding acknowledgement The research was supported by the projects Solarium (ANR-14-CE05-0025) and Platofil (ANR-14-CE26-0020) granted by the French National Grant Agency (ANR). Travelling support from Barrande/PHC project promoting collaboration between LPICM and ACVR. CEITEC 2017, April 27, Brno, Czech Republic martin.foldyna@polytechnique.edu