Simple and scalable fabrication approaches of Nanophotonic structures for PV

Transcription

1 Simple and scalable fabrication approaches of Nanophotonic structures for PV Fabien Sorin Surface du Verre et Interfaces (SVI), UMR 125 CNRS/Saint-Gobain, 39, Quai Lucien Lefranc, Aubervilliers, Cedex, France JNPV, December 12th 2012

2 2 Outlook Context and Challenges Nanophotonic structures and fabrication strategies Bragg mirrors: how to stack films of different optical properties Diffraction gratings: using nanoimprint Lithography Plasmonics: self organized metallic nanoparticles Conclusion

3 3 Surface du Verre et Interface (SVI) A unité Mixte de Recherche CNRS / Saint-Gobain Recherche In Aubervilliers near Paris 12 researchers and engineers 10 Students and Postdocs Research topics Heterogeneous Reactive Materials Making Glass Thin films and Nanostructures Functionalizing Glass Expertise in Nanostructures and thin-film processing Nanostructures optical properties A strong focus on PV

4 4 Saint-Gobain Context Strategy of energy efficient habitat Heat management Lighting: Natural / efficient artificial Energy production and storage: PV! Photovoltaics at SG Saint-Gobain Solar Thin-film technology : Avancis See Dr. Arouna Darga (LGEP) Poster (CZTS cells)! Light management is an old theme at SG: Anti-reflection coatings Saint-Gobain Glass: Albarino Glass Albarino Glass Can we use and develop processes for Nanophotonic structures?

5 5 Motivation and Challenges Improve light absorption in ultra thin layers Why go thin? How? Reduce production costs (reduced material usage, higher throughput) Avoid material shortage Usage of materials with poor electronic properties Flexible substrates Challenge: loss of absorption? Coherent light trapping in 1 µm thick layer using guided modes and local field effects Bragg mirrors (1D Photonic crystals) Gratings (2D Photonic crystals) Plasmonic (Scattring of matallic objects) Materials and Processes Challenge: Surface area, Price and Compatibility

6 6 Distributed Bragg Reflectors: Principle Absorbing medium Distributed Bragg Reflector

7 7 Bragg Mirrors: Fabrication approach High and low index refraction layers from scalable liquid-based processing Process already in use for some Saint-Gobain products High index layer Lox index layer Dense TiO2 layer Dépôt spin-coating Calcination (450 C, 1h) Porous layer (50 à 70%, 60nm): SiO 2 + Latex de PMMA puis calcination (450 C,1h) e=135nm MEB MEB e=140nm n TiO2 ~ 2,07 (in NIR) n SiO2p ~ 1,17 (in NIR) MEB

8 8 Bragg Mirrors: First results 10 layers 3 x 3 cm 2 Substrat 8 layers structure Almost 90% reflection - SiO 2 50% porosity e = 140nm +/- 3nm - TiO 2 dense e = 104nm +/- 11nm See Barbara Brudieu s poster!! Normal Incidence

9 9 Gratings: principles Periodic texturation for improved coupling of incident light to absorbing layer Objective: coupling free space propagating light to confined states in the layer Extensive work in litterature Using propagative guided modes At the front or at the back of the cell Optical coupling depdends on materials, Indices, period optimization needed Grating can be carved in the material itself Recent review: Mokkapati & Catchpole, JAP 112, (2012) Absorbing medium Using evanescent modes Absorption can surpass the Yablonovitch limit Yu et. al., PNAS 107, (2010) Structures with feature sizes of 1x10-7 m over 1x1 m 2!!

10 10 Gratings: Fabrication Simple process: NanoImprint Lithography (NIL) Mask: Small Silicon master made by lithography Reported on PDMS mold Repeated use of one master Imprinted layer: Sol-gel process and deposition by spin coating Low pressure and low temperature I PDMS stamp, II gel thin film, III glass substrate, IV silica based textured film C. Peroz et. al., Advanced Materials 21, 555 (2009) J. Teisseire et. al., APL (2011)

11 11 Gratings: results Large area : Step and repeat process Optimization of structure for light trapping 200nm thick GaAs absorber Optimization on Λ, ff and h, 1D structure using RCWA Reach 40% increase in absorption See poster: NIL of silica material!

12 12 Plasmonics: what use for PV? - Resonant excitation of surface plasmons-polaritons and confinement of EM energy at the metal-semiconductor interface - Resonant excitation of local surface plasmons in nanoparticles embedded in absorbing medium - Scattering of light and coupling to guided modes S. Basu Mallick et al, MRS Bulletin 36 (2011) Ferry et al, Optics Express 18, A237 (2010) (50 % increase in efficiency)

13 13 Plasmonic Structures We are developping a process to self-organize metallic nanoobjects over large area Preliminary experimental and theoretical results Flat layer 5µm NP array Reflection and transmission measurement at normal incidence With integrating sphere Evidence of scattering resonance on reflection and transmission spectrum

14 14 Plasmonics: simulation Simulation tool: Rigorous Coupled Wave Analysis (RCWA) for periodic structures Top view a Definition of system: Square nanoparticles Geometrical cross section as measured on SEM pictures Volume of silver layer conserved See Arthur Le Bris s Poster!

15 15 Conclusions We realized light trapping structures using simple and scalable fabrication approaches The optical effects targeted have been characterized and modeled Next steps: effect of the structure on light absorption, on J sc and overal efficiency. Structures optimization: ordered vs random, front vs back, etc Posters: «Plasmonic structures for enhanced light absoprption in ultra thin sloar cells» A. Le Bris «Light trapping structures for thin-film solar cells» B. Brudieu «NIL for silica materials» J. Teisseire

16 16 Collaborators Surface du verre et interfaces Barbara Brudieu Arthur Le bris Fatah Maloum Jérémie Teisseire Elin Sondergard Etienne Barthel Laboratoire de la Physique de la matière condensée (Ecole Polytechnique) Barbara Brudieu Géraldine Dantelle Prof. Thierry Gacoin Saint-Gobain Recherche François Guillemot Thank You!