NSF EPSCoR Kansas Center for Solar Energy Research Annual Program Review June 12-14, 2011 Plasmonic and Photonic Photovoltaics based on graphene and other carbon nanostructures Fengli Wang, Guowei Xu, Jianwei Liu, Caitlin Rochford, Judy Wu Department of Physics and Astronomy, University of Kansas In collaboration with Cindy Berrie, and Tina Edwards Department of Chemistry, University of Kansas Jun Li Department of Chemistry, Kansas State University Ron Hui, Qian Wang Department of Electrical Engineering and Computer Science Francis D Souza, and Navaneetha Krishnan Department of Chemistry, Wichita State University 1 1
Three Generations of Solar Cells I) Wafer based Silicon Lab record: 25% Module record: 23% II) Thin-film Different semiconductor(s) Reduced material cost Lab record: 26% (GaAs) 17% (CdTe) 10% (a-si) Module record: 20% (pc-si) III) Advanced thin-film Circumvent 1 st gen. theoretical limit Maintain low cost Lab record: 34% (tandem) Module record: --- Efficiency, % 100 80 60 40 20 US$0.10/W Enhance efficiency II III Projections: US$0.20/W Goals: ~ 30 /W P ~ 2 /kwh 0 100 200 300 400 500 Cost, US$/m 2 I Ultimate thermodynamic limit at 46200 suns Ultimate thermodynamic limit at 1 sun Shockley- Queisser limit US$2.50/W Reduce cost
Principle of Semiconductor Solar Cells Manipulation of photon absorption and electron transport at nanoscale is the key to high efficiency and low cost PV devices.
Conductivity and Photoconductivity COOH 0.4 CNF/TiO2 nanowire Dia: 90-140 nm 0.2 Spacing between probes: 1-1.5 µm 0.0 Crystallinity in TiO2 shell critical to photocurrent transport Improved dark conductivity and photoconductivity in annealed sample Rochford, C.; et al,. Applied Physics Letters 2010, 97 (4), 043102. Z.Z. Li et al, Nanoscale Research Letters 2010, 5, 1480. COOH hν Current (µa) Current (µa) 1.4 1.2 1.0 0.8 0.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 Li-KSU and Wu-KU S1, Dark S1, 1 Sun S2, Dark S2, 1 Sun annealed 0 10 20 30 40 Voltage (mv) S1, with Dye, Dark S1, with Dye, 1 Sun S2, with Dye, Dark S2, with Dye, 1 Sun annealed 0 10 20 30 40 Voltage (mv) 4
Photonic and Plasmonic photovoltaic Enhanced light absorption via promoted light interaction with photonic or/and plasmonic nanostructures Atwater and Polman, Nat. Mat. Feb. 2010 doi: 10.1038/nmat2629 5
Photonic FTO Photonic dye-sensitized solar cells Hui, Wu KU, D Souza-WSU) Diffraction effect after N3 dye Current Density (A/cm 2 ) 0.0025 0.0000-0.0025-0.0050 wieght line - patterned light line - unpatterned 22 mw -0.0075 32 mw 72 mw 105 mw -0.0100-0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 Potential (V) Efficiency improved dramatically F.L. Wang et al, preprint. 6
On-going work: plasmonic+photonic transparent electrodes Ag nanoparticles on FTO photonic crystals TiO 2 FTO Silver particles Normalized Power absorption 1 0.9 0.8 0.7 Flat interface 0.6 With FTO hemisphere and silver nano particles 0.5 0 0.5 1 1.5 2 2.5 3 Depth into TiO2 layer (µm) With FTO hemisphere (a) Poster by F.L. Wang et al 7
Plasmonic graphene-based solar cells in collaboration with Berrie, Hui, Li, D Souza National Renewable Energy lab, Argonne Nat. lab, Oak Ridge Nat. lab, Iowa State Univ., Univ. of Arkansas Advantages of graphene: Ultra-thin Low cost Abundance of carbon Compatible thermal budget to that of Si (nc and amorphous) films Issues: Improved light scattering required for thin film PVs Interface between graphene and PV materials Industrialization
Graphene: a promising transparent electrode Massless Dirac fermions with high Fermi speed V f ~10 6 m/s high mobility μ ~10 6 cm 2 /Vs σ=enμ high conductivity σ at low carrier density n due to high μ; σ min ~4e 2 /h even at low carrier density 9
Optical Properties of Graphene Gapless semiconductor or semi-metal Fresnel equation in thin film limit: Transmittance Absorption Reflection <0.1% Transparent conductors IR detectors Bio-/chemical-sensors P. Avouris, Nano Letters 10, 4285(2010) 10
Graphene photonic crystals Fabricated using nanoimprint lithography J.W. Li, et al, APL (accepted with minor revisions) and poster by Jianwei Liu et al 11
Optical Transmittance Transmittance vs. conductivity Electrical Conductivity A unique scheme to improve both optical transmittance (broad band) and electrical conductivity 12
Plasmonic graphene: low-cost and high performance PVs In collaboration with NREL, KSU (Li), Hui and Berrie (KU), D Souza (WSU) 300 nm Si Silver hemisphere 1nm thick graphene Plane wave illumination Ag nanoparticles on graphene: sheet resistance reduced by 2-4 times light scattering for enhanced absorption at small solar cell thickness 13
Generating plasmonic graphene Self-assembled Ag nanoparticles on graphene Diameter: 30-80nm Ordered Ag nanoparticles on graphene Diameter: 150-250nm A large range of controlled geometry has been demonstrated. Poster by Guowei Xu et al, preprint. 14
Enhanced light scattering in plasmonic Graphene 10 times enhanced Raman peaks suggest strong light scattering on plasmonic graphene Confirmation of light scattering also in transmission spectra 2-4 times enhanced conductivity Transmittance 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 300 400 500 600 700 800 Wavelength (nm) G_14nm AgNPs G_8nm AgNPs G_4nm AgNPs 15
Summary Carbon-based nanostructures provide a fascinating system for physics studies and are promising for many optical and optoelectronic applications 16
University of Kansas Thin Film and Nanoscience Group July 27, 2010 Dr. Jianwei Liu Guowei Xu Caitlin Rochford Dr. Rongtao Lu Dr. Fengli Wang Dr. Bing Li Caleb Christianson Alan Elliot Gary Melek Logan Wille Mike Dunaway Jon Gregory Richard Lu External collaborations: ANL: Zhijun Chen and Vic Maroni LANL: Javier Baca ORNL: Amit Goyal and Parans Paranthaman NREL: Yanfa Yan 17