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

2. 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)

3. 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

4. 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, (2005); E. Garnett and P. Yang, Nano Letters 10, 1082 (2010).
CEITEC 2017, April 27, Brno, Czech Republic

5. 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

6. Plasma enhanced vapor-liquid-solid growth
CEITEC 2017, April 27, Brno, Czech Republic

7. Bottom-up solar cell fabrication
CEITEC 2017, April 27, Brno, Czech Republic

8. 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

9. 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, (2013) 
CEITEC 2017, April 27, Brno, Czech Republic

10. 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, (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

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

12. Improving energy conversion efficiency
CEITEC 2017, April 27, Brno, Czech Republic

13. 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,
CEITEC 2017, April 27, Brno, Czech Republic

14. 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

15. 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

16. 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-CE ) and Platofil (ANR-14-CE ) 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