Thin-film Silicon Photovoltaics Miro Zeman Delft University of Technology, Photovoltaic Materials and Devices group
Outline 1. Introduction 2. Cost and performance 3. Key challenge: Increasing efficiency New materials Light trapping Nano-imprint lithography Modeling New concepts 4. Summary and outlook
LATEST ACHIEVEMENTS
Record thin-film Si solar cell: Stabilized efficiency LG Electronics record solar cell Triple junction: a-si/μc-si/μc-si) Courtesy of Dr. Heon-Min Lee, LG Electronics Advanced Research Institute
1 INTRODUCTION
Message Matured low-cost technology with potential for further cost reduction Suitable for very large-scale (TW) implementation Sunbelt regions, BIPV Global research effort to enhance the performance Focus: Light management, thin design, new materials and concepts All PV technologies can benefit from the achievements
2 COST AND PERFORMANCE
Oerlikon Solar THINFAB TM 140 production line Some unique features: Lowest module manufacturing cost: 0.35/Wp enabling electricity production at 0.07/kWh Guaranteed performance: 10.8% module efficiency, >97% fab yield, 140 MW fab output Fastest module energy payback time: less than 1 year Clean module design: no toxic elements and lowest CO 2 footprint of 21g CO 2 /kwh Source: OERLIKON SOLAR (http://www.oerlikon.com/solar/thinfab/downloads/factsheet_thinfab.pdf)
Competitive performance of micromorph modules Oerlikon Solar outdoor test facility (Arizona/USA) Courtesy of Dr.Juergen Sutterluetti and Dr.Stefan Sellner OERLIKON SOLAR
Competitive performance of micromorph modules c-si (class A): P nom : 220 Wp with Cum. Energy Yield [kwh/kwp] = 3336 kwh Micromorph: P nom : 125 Wp with Cum. Energy Yield [kwh/kwp] = 3450 kwh (+3.4%) Courtesy of Dr.Juergen Sutterluetti and Dr.Stefan Sellner OERLIKON SOLAR
HyET Solar flexible modules Unique product and technology A flexible and lightweight PV product for application on lightly constructed rooftops with a very large world wide market Product passed the IEC certification tests successfully Broad technology based on roll-to-roll deposition steps, wet chemical steps as well as lamination steps Courtesy of Dr. Edward Hamers, HyET Solar
3 KEY CHALLENGE: Increasing efficiency
State-of-the-art Modules: Best thin-film Si R&D modules: 11-12% Commercial modules 6-10% (total area efficiency) Best thin c-si on glass mini-module 10.4% (CSG Solar) Solar cells: Best thin-film Si solar cells: η in = 16.3% (USSC triple-junction solar cell) η st = 13.4% (LG Electronics triple-junction solar cell) Challenge: Stabilized efficiency of thin-film Si solar cells > 20 %
Increasing efficiency Delicate interplay: Material and interface processing Defect engineering (V oc, FF) Spectral utilization Multi-junction concept Intermediate reflectors (η) Light trapping Rough interfaces Back reflector, TCO (J sc ) International research effort to increase the efficiency
Thin-film Si solar cell structures: superstrate configuration Single-junction Double-junction Triple-junction Glass plate Glass plate Glass plate TCO TCO TCO a-si:h μc-si:h a-si:h a-si:h a-sige:h μc-si:h a-si:h a-sige:h/μc-si:h a-sige:h/μc-si:h TCO Metal η st =10.1% (a-si) Oerlikon η in =10.9% (μc-si) EPFL-IMT TCO Metal η st =12.3% (a-si/ μc-si) Kaneka η st =12.3% (a-si/ μc-si) Oerlikon* TCO Metal η st = 13.4% (a-si/μc-si/μc-si) LGE
Thin crystalline Si solar cell on glass Glass plate Intermediate layer p-type Crystalline silicon (total thickness 5-10 μm) Metal n + -type resist Metal η=4.7% (EBC 10 μm pc-si) HZB η=8.4% (LC 10 μm pc-si) UNSW+Suntech Si deposition process: 1. Crystallization of a-si films Deposition of a-si (PE-CVD) Crystallization of a-si layers (Solid phase crystallization) 2. Crystallization of Si films Deposition of Si (e-beam evaporation or sputtering at elevated temperatures) Crystallization of Si layers (Line-shaped e-beam and laser crystallization)
3.1 IMPROVING EFFICIENCY: New materials
New materials: Amorphous and microcrystalline Si alloys Application in tandem a-si/μc-si solar cell ZnO Back contact n- SiO X µc-si:h (1.1μm) p- SiO X n- SiO X a-si:h ZnO Front contact 250 nm p-sio x Glass 1 μm M. Despeisse et al,, Physica Status Solidi A, 208 (8), 2011. (EPFL-IMT)
3.2 IMPROVING EFFICIENCY : Light trapping
Light trapping: Scattering at rough interfaces Flat surface Randomly-textured surface Modulated surface texture Modulated multisurface texture Glass Glass Glass Glass TCO TCO TCO TCO Si Si Si Si TCO TCO TCO Metal Metal Metal Metal multi-step processes in TCO deposition multi-surface approach
Light trapping: Scattering at rough interfaces Modulated surface-textured substrates σ RMS = 221 nm σ RMS = 297 nm Tokyo Institute of Technology Delft University of Technology A. Hongsingthong et al., Applied Physics Express 3 (2010) 051102. (Tokyo Tech) O. Isabella, J. Krč, and M. Zeman, Applied Physics Letters 97, 101106 (2010). (TU Delft)
Light trapping: Modulated surface textures Manipulation of scattering level EG1 σ RMS = 297 nm 1.0 0.9 0.8 0.7 EG3 σ RMS = 630 nm H T 0.6 0.5 EG5 σ RMS = 742 nm 0.4 0.3 0.2 0.1 Flat glass / AZOR (ref.) EG1-based substrates EG2 / AZOR EG3 / AZOR EG4 / AZOR EG5 / AZOR EG1 / AZOR EG1 (offset) 0.0 300 400 500 600 700 800 900 1000 1100 Wavelength [nm] O. Isabella, P. Liu, B. Bolman, J. Krc, M. Zeman, Mater. Res. Soc. Symp. Proc. Vol. 1321, 2011. (TU Delft)
Light trapping: Modulated surface textures Improved AR and scattering 1.0 Single-junction a-si solar cells 0.9 0.8 J ph = +8.46% 0.7 0.6 EQE 0.5 1 μm 0.4 0.3 0.2 0.1 0.0 Flat glass / AZOR (1.2 m) EG5 / AZOR (1.2 m) 400 500 600 700 800 Wavelength [nm] O. Isabella, P. Liu, B. Bolman, J. Krc, M. Zeman, Mater. Res. Soc. Symp. Proc. Vol. 1321, 2011. (TU Delft)
3.3 IMPROVING EFFICIENCY : Nano-imprint lithography
Light trapping: Scattering and diffraction Nano-imprint lithography Any rough morphology possible with high-fidelity Periodic surface textures (1-D and 2-D diffraction gratings) Decoupling optical and electrical properties of electrodes Thin TCO layers (suppressing parasitic absorption) New concepts (3-D solar cells, plasmonics, nano-antenas) Texture A stamp PDMS Nano-imprinting stamp Texture A Master Master Replica Replica
Light trapping: Scattering at rough interfaces Nano-imprint + new TCO layer (In 2 O 3 :H (IOH)*) Master ZnO back Replica incoming light incoming light mc-si:h interlayer a-si:h ZnO front ZnO back mc-si:h interlayer a-si:h In 2 O 3 :H NIL resin C. Battaglia et al., Nano Letters 11, 661 665, 2011. (EPFL-IMT) *T. Koida, H. Fujiwara, and M. Kondo, Japanese Journal of Applied Physics,46(28), L685, 2007. (AIST)
Light trapping: Scattering at rough interfaces Nano-imprint + new TCO layer Flat Substrate J top sc ZnO back [ma/cm 2 ] mc-si:h J bottom sc [ma/cm 2 ] V oc [mv] FF Eff [%] [%] Master 11.9 12.1 1385 72.6 12.0 a-si:h Replica+ITO 12.4 11.8 1362 69.5 11.2 In 2 O 3 :H glass Replica+InO:H 12.9 13.0 1359 68.7 12.0 Flat+InO:H 10.4 6.7 1421 81.2 7.7 25.9 ma/cm 2 with 250nm a-si, 30nm IRL, 1.1 μm μc-si No AR coating. C. Battaglia et al., Nano Letters 11, 661 665, 2011. (EPFL-IMT) Ch. Ballif et al., PV-IEEE, 2012. (EPFL-IMT)
Light trapping: Periodic diffraction gratings Angle-selective manipulation of light scattered at the rough interfaces using 1-D and 2-D diffraction gratings Grating structures fabricated by OM&T, Moser Baer
Light trapping: Random versus periodic texture Glass Glass TCO TCO Si TCO Metal Si TCO Metal Absorption enhancement: Random texture 4 n 2 Periodic (square) texture π 4 n 2 Periodic (triangular) texture 2π/ 3 4 n 2 (thick film, single wavelength) Yablonovitch et al., JOSA, 1982. Z. Yu, A. Raman and S. Fan, Optical Express, 2010. (Stanford University) F.-J. Haug, K. Söderström, A. Naqavi, and C. Ballif, J. Appl. Physics 109, 084516, 2011. (EPFL-IMT)
3.4 IMPROVING EFFICIENCY: Modeling
3-D optical modeling: Single-junction solar cell Optimization of 2-D gratings and evaluation of absorption losses Absorptance and optical losses 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 2 D grating: P 1 = 600 nm, P 2 = 600 nm, h = 300 nm 2-D 15.87 ma/cm 2 1-D 13.80 ma/cm 2 Flat 11.54 ma/cm 2 0.0 350 400 450 500 550 600 650 700 750 800 850 900 950 1000 Wavelength [nm] R Front ZnO:Al p n Back ZnO Ag i - 2-D gratings i - 1-D gratings Flat O. Isabella, S. Solntsev, D. Caratelli and M. Zeman, Progress in Photovoltaics, 2012. (TU Delft)
3-D optical modeling: Triple-junction Si solar cell Optimization of 2-D gratings and intermediate and back reflectors 1.0 0.9 35.32 ma/cm 2 IOH (125 nm) IR1 (30 nm) IR2 (80 nm) i bottom nc-si (2800 nm) i top (175 nm) i middle (175 nm) Absorptance [-] 0.8 0.7 0.6 0.5 0.4 0.3 31.30 ma/cm 2 25.43 ma/cm 2 Schockley-Queisser limit 43.33 ma/cm 2 (350-1110 nm) 30.66 ma/cm 2 BAZO (70 nm) Ag (100 nm) 0.2 0.1 0.0 Target: J Ph-tot = 30 ma/cm 2 η= 17% No light trapping (2 passes) Tjedje-Yablonovitch limit Deckman-Wronski limit nc-si:h on 2-D gratings 400 500 600 700 800 900 1000 1100 Wavelength [nm] O. Isabella, M. El-Shinawy, S. Solntsev, M. Zeman, OSA conference, Eindhoven, 2012. (TU Delft)
3.5 IMPROVING EFFICIENCY: New concepts
Plasmonics Localized surface plasmon resonance in Ag NPs Resonance wavelength can be tuned to NIR R. Santbergen et al., Journal of Optics 14, 024010, 2012 (TU Delft) C. Eminian et al., Prog. Photovolt., 19, 260, 2011 (EPFL-IMT) E. Moulin et al., Thin Solid Films, 516, 6813, 2008 (FZ Julich)
Plasmonics ITO a-si:h/µc-si:h Textured BR σ RMS =40nm Plasmonic BR σ RMS =22nm Ag NPs BR ZnO:Al Ag Glass Broadband high haze factor Smooth surface for high-quality film growth H. Tan, R. Santbergen, A.H.M. Smets, M. Zeman, Nano Letters 12, 4070, 2012. (TU Delft)
Plasmonics Comparable to state-of-the-art surface-textured substrate Strong scattering without introducing high surface roughness No degradation of V oc and FF compared to a-si flat cell H. Tan, R. Santbergen, A.H.M. Smets, M. Zeman, Nano Letters 12, 4070, 2012. (TU Delft) H. Tan, R. Santbergen, G. Tao, A.H.M. Smets, M. Zeman, IEEE-JPV, 2012. (TU Delft)
Flattened Light-Scattering Substrate (FLiSS) Flat FIG. 1. Concept of the FLiSS for thin-film solar cells. 2-D photonic crystal with flat surface High-quality Si active layer (high V oc and FF) Light trapping in the IR region (high J sc ) H. Sai et al., Applied Physics Letters 98, 113502, 2011.
Flattened Light-Scattering Substrate (FLiSS) FIG. 5. J-V curves and corresponding J-V parameters of the μc-si:h cells (1 μm thick) fabricated on a flat substrate, a reference textured substrate, a 2D ZnO grating and a FLiSS. H. Sai et al., Applied Physics Letters 98, 113502, 2011.
FLiSS substrate optimization 1.0 0.9 450 nm inverted pyramid Absorptances and reflectance [-] 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 Total J ph = 46.19 ma/cm 2 R (9.45 ma/cm 2 ) Front IOH (3.43 ma/cm 2 ) p + n (1.17 ma/cm 2 ) ZnO:Ga (type a) (1.44 ma/cm 2 ) Dead (n) a-si:h (2.19 ma/cm 2 ) Ag (1.08 ma/cm 2 ) i-layer (27.43 ma/cm 2 ) 1 μm μc-si:h 2000 nm 0.0 300 400 500 600 700 800 900 1000 1100 1200 Wavelength [nm] O. Isabella, H. Sai, M. Kondo and M. Zeman, IEEE-JPV, 2012
Thin crystalline Si on glass: new concepts E-beam crystallized Si material: Nanostructuring process: Nanosphere lithography (NSL) Reactive ion etching (RIE) Si nanowires High light absorption, new concepts for cell structures S. Schmitt et al., Nano Letters, 2012. (Cooperation Max-Planck-Institut Erlangen and Helmholtz Zentrum Berlin)
SUMMARY and OUTLOOK
Summary Performance (η>20%): Increase V oc (growth on textured substrates) Si quantum dot New materials: Absorber materials stable against LID Si based alloys with O, C, and Ge Light management: Low absorption TCOs and ARC 2-D or 3-D PC based flat substrates Novel 2-D or 3-D solar cell structures New ideas and concepts are welcome Si nanowires 100 nm S. Perraud et al., PSS-C, 2012 (Snapsun project) S. Schmitt et al., Nano Letters, 2012. (Cooperation Max-Planck-Institut Erlangen and Helmholtz Zentrum Berlin)
FP7 Project Fast Track 20 participants 10 research partners 10 industry partners Duration: March 1 st 2012- Febr. 28 th 2015 Contribution: 9.300.000 EU Aims: Redesign TFSi solar cells, Up-scaling of nano-imprinted substrates Bringing this next-generation technology towards the market with 12% module efficiency Development of a low-cost large-area deposition technology see Poster 3DV.1.45 Courtesy of Dr. Aad Gordijn, (FZ Jülich)
Future research outlook Solar cell structure: Thin-film Si based multi-junction cells J ph (300-1100nm)=43.2 ma/cm 2 EQE=0.70 V oc /E gap =0.55 FF=0.75 η 3stack = 18.3% η 4stack = 21.2% Glass plate Front contact Top cell (E gap =1.95eV) a-si, a-sic, a-sio Top middle cell (E gap =1.47eV) a-sige:h Bottom middle cell (E gap =1.12eV) nc-si Bottom cell (E gap =0.75eV) nc-sige Back contact
Future research outlook Solar cell structures: Single-junction c-si film solar cell J ph (300-1100nm)=43.2 ma/cm 2 EQE=0.80 V oc /E gap =0.65 FF=0.80 η 1stack = 21.0% Glass plate Intermediate layer Crystalline silicon (total thickness 5-10 μm) Metal Si resist Metal
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