Solar Selective Absorber Coating Methods Plasma Processes Paul Gantenbein & Elimar Frank SPF - Institut für Solartechnik University of Applied Sciences Rapperswil (HSR)
Optical properties of a selective absorber Optical properties of solar selective absorbers a AM1.5 e T C ( / ) Wien s displacement law: AM 1.5 ideal characteristics Temperature T ( C) Wavelength l max (mm) 200 6.1 250 5.55 300 5.05 500 3.75 thermal radiation @ 100 C 600 3.33 visible range Wavelenght l (mm) Thermodynamics: 2. Law 2
Design types of selective absorber - Intrinsic selective material - Surface texture / geometrical structure - Semiconductor-Metal Combination - Multilayers - Metal-Dielectric - Solar-transmitting / Blackbody-like Nb on Si Structural absorber with transition wavelength l = 1 mm 3
Structural absorber - morphology Thronton-Diagram Ann. Rev. Mater. Sci 1977: 239-260 (Graph: A. -M. Valente-Feliciano) Physical (parameters) processes establishing structural zones film morphology. 4
Substrates for combined absorbers 5
Substrates for combined absorber tubes 6
Substrates for combined absorber tubes 7
Plasma process for absorber preparation RF/MF Power DC Power Target Plasma Substrate Match Box RF Filter Vacuum Chamber to ESCA Machine Deposition Chamber Sample Holder Sample Stack Magnetron Target Sample Heating Magnetron: E B Pressure Control Valve Ar CH 4 / O 2 Process Gases N Experimental 2 / O Setup 2 Vacuum Pumps Reactive Magnetron Sputtering Target Materials: Cr, W, Ti, Ag, Au, Nitrides ) Process Gases: noble gases / reactive gases www.angstromsciences.com 8
Plasma Process Technology Components Magnetron Technology planar / circular http://www.vonardenne.biz Magnetron Technology: http://www.vonardenne.biz http://www.angstromsciences.com D. Depla et al. Plasma Deposition Processes 9
Coating Methods - RF excitation system Plasma Ignition Frequency Electrical Parameters Lindas Pranevicius - Coating Technology Handbook 10
Coating Methods Ion Energy / Sputter Yield ev to K: 1eV~1.16*e4K Schematic of a cathodic arc deposition system. Emission characteristics of a cathodic arc source. H. Randhawa - Coating Technology Handbook 11
Coating Methods / Plasma potential Electrical Parameters / Ion Energy floating metal surface (sheet) Ion Energy / Sputter Yield ev to K: 1eV~1.16*e4K Electron cross-section in Argon. Sputter yield Y as a function of the Ar+ ion energy at normal incidence in a magnetron sputtering process. Schematic illustration of the plasma sheaths which form between a plasma apparatus walls for large anode and small anode. Scott G. Walteon and J. E. Greene Plasma Deposition Processes 12
CERMET absorber surface Substrate Bias Voltage Surface roughness optical & stability behaviour SEM AFM Dielectric/Cr 120 nm a-c:h/cr CERMET auf on Si REM-Lab Uni BS R a = R a (U B ) U B Structural absorber with transition wavelength l = 1 mm 13
Chemical composition of an absorber coating Process Gas Composition / Substrate Temperature rf-power Structural absorber with transition wavelength l = 1 mm 14
Multilayer Absorber Reflection R(l) in function of Wavelength l - sandwich layer layer Schichtdicken thickness C1 (n, Chromanteil k) d= d = d1, d1; d2, d2; d3 d3 (nm) [nm] R(l) no SiO 2 R(l) d1 SiO 2 R(l) d2 SiO 2 R(l) d3 SiO 2 R(l) d4 SiO 2 120 nm (n L ) (n f ) CERMET 4 3 2 1 Cu (n s ) Multi-layer on IR-Reflector 15
Scale up of substrate bias - Plasma Potential variation Absorber film properties depending of the plasma potential / Bias Patentschrift: DE 198 30 404 B4 16
Multilayer solar selective absorber Cermet / SiO 2 1.0 0.9 0.8 AM 1.5 BB 373 K Reflectance R(l) [-] 0.7 0.6 0.5 0.4 0.3 1) 120 nm 0.2 2) 0.1 0.0 0.3 0.4 3) a-c:h/cr CERMET C E R - M a-c:h E + T - SiO 2 0.6 0.8 1 1.5 2 3 4 6 8 10 15 20 Wavelength [mm] REM-Lab Uni BS R(l) of three multilayer systems on copper metal sheets. a sol = 95.0 % to a sol = 95.2 % ; e th = 3.1 % to e th = 3.7 %. 18
Absorber Coating Process Parameter List (incomplete) Geometry: Substrate Surface Orientation to Plasma Source Vacuum Chamber design Vacuum Chamber: Base Pressure / Rest Gases Vacuum Pump Technology Plasma Ignition: Reactant : Substrate: Time: Frequency (DC, MF, RF, HF) Plasma Generator Technology / Plasma Density Coating Material Educt / Target Material / Process Gases Process Pressure / Plasma Density Material (el. behaviour) Roughness Temperature Speed Coating time 19
Tube Absorber Coating Machine Harding G. L.; US Patent 4309261 (1982) 20
Tube Coating Machine High Temperature Solar Selective Absorber Coatings Tube Holder (n tubes) D H Step 4 Step 3 Von Ardenne GmbH Postanschrift: Plattleite 19/29 01324 Dresden Deutschland L T Step 1 Process Flow Direction Step 2 L L = length of the coating machine 39m L T = length of the tubes 4m D H = Diameter of the tube holder 1.8m D T = Diameter of the Absorber tube 70mm Source: Von Ardenne GmbH Plattleite 19/29 01324 Dresden Germany 21
Selective absorber - literature CERMET CERMET W-Al Mo-Si 2 O 3 N 4 3 A. R. Antonaia Escobar-Galindo et al. et al. 23
Thank you for your attention! paul.gantenbein@solarenergy.ch www.solarenergy.ch 24