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2007 SNEC International Solar&PV ConferenceAdvanced Hybrid Silicon Solar Cells Dr.Guoxiao Yao CTO of Tianwei Yingli New Energy Resources Co.姚国晓博士姚国晓博士 首席技术官首席技术官 中国天威英利新能源有限公司中国天威英利新能源有限公司 2007年年5月月10日日2007 SNEC International Solar&PV C2007 SNEC International Solar&PV Conference1.Features of Metallization for Screen Printing Silicon Solar Cells2.Features of Metallization for Buried Contact Silicon Solar Cells3.Features of Metallization for Hybrid Silicon Solar Cells4.Processing Technology of Metal Stencils5.Laser-Processed Single-Level&Double-Level Stainless Steel Stencil6.Performance of Hybrid Silicon Solar Cells 7.ConclusionsC2007 SNEC International Solar&PV ConferenceAdvantages:1.Good availability of screen printing machine&firing furnace in the market;2.Simplicity of processing sequence.Disadvantages:1.Relatively wider finger width(150 um),leading to higher shading loss(10%);2.Relatively lower height-to-width aspect ratio(0.06),leading to higher resistive loss,lower FF.3.Lower opening percentage(40%)of screen&gradual degradation of printing lines with the wear and tear of the emulsion layer.Features of Metallization for Screen Printing Solar Cellsrear metal contact2-3 mm150 umFigure 1:The structure of screenprinting solar 2007 SNEC International Solar&PV ConferenceAdvantages:1.Very fine top finger width(25 um),leading to lower shading loss(3%);2.Pretty high height-to-width aspect ratio(as high as 5),leading to lower resistive losses,higher FF;3.Lower contact resistance,further reducing the resistive loses,increasing FF.Disadvantages:1.Much longer metallization process;2.Consuming more wet chemicals,less environmentally friendly.Figure 2:The structure of buried contact solar cells25 umFeatures of Metallization for Buried Contact Solar C2007 SNEC International Solar&PV ConferenceFigure 3:Schematic of a hybrid silicon solar cell structureSP Ag contactp-typeP+n+n+oxideSP Al contact50 umA hybrid solar cell incorporates some of the advantages of buried contact and screen printing technologiesAdvantages:1.Relatively fine top finger width(50 um),leading to lower shading loss(6%);2.Relatively high height-to-width aspect ratio(0.5),leading to lower resistive losses,higher FF;3.Simplicity of processing sequence.Disadvantages:1.Mask manufacturing process complicated&costly;Features of Metallization for Hybrid Solar C2007 SNEC International Solar&PV Conference1.Mask fabrication2.Pattern alignmentKey T2007 SNEC International Solar&PV ConferenceAperture Profile:Cell sideSqueegee side40 mFoilLaserGaussian beam profile:Metal Stencil F2007 SNEC International Solar&PV ConferenceAperture Profile:40 m35 m40 mCell sideSqueegee sideFoilLaserGaussian beam profile:Aids paste transfer!Metal Stencil F2007 SNEC International Solar&PV ConferenceFinished stencilLocal structureFingerStainless Steel Foil Busbar bridgeBusbarSingle-Level Stainless Steel S2007 SNEC International Solar&PV Conferencea stencil-printed finger&busbar68 m(W)x 24 m(H)finger profileProfile of Printed L2007 SNEC International Solar&PV ConferenceDouble-levelBusbar bridgeDouble-levelBridges betweenFinger&busbarDouble-levelFinger bridgeFirst Level=Wire Mesh of a Conventional ScreenSecond Level=Wire Mesh+EmulsionBottom ViewSide ViewDouble-Level Stainless Steel S2007 SNEC International Solar&PV ConferencePrinted FingerPrinted BusbarSingle-LevelStencil PrintingDouble-LevelStencil PrintingPrinting Comparison 2007 SNEC International Solar&PV ConferenceFigure 25:(a)The grooves just after laser scribing shows some islands;(b)the clean grooves after laser scribing and chemical etching.Oxide0.014Single scribingIsland1.67(a)OxideFormed wider groove0.050.026 1.670.05(b)Features&Formation of the G2007 SNEC International Solar&PV Conference1.Print a test pattern on a dummy waferWafer nestStencilA2007 SNEC International Solar&PV Conference2.Indicate 8 alignment points using the laser vision systemPut a pic about laser boxA2007 SNEC International Solar&PV Conference3.Calculate the translation and rotation with respect to the print nestrA2007 SNEC International Solar&PV Conference4.Translate and rotate the groove scribe pattern using softwarer,A2007 SNEC International Solar&PV Conference5.Laser scriber now registered to the stencil print nestr,A2007 SNEC International Solar&PV Conference6.Proceed to cut grooves on process wafersWafer nest7.The stencil is pre-aligned to print directly into the groovesA2007 SNEC International Solar&PV ConferenceFinger Profile:50 m wide&22 m highBusbar Profile:230 m wide&22 m highStencil Printed Finger&Busbar 2007 SNEC International Solar&PV ConferenceCell Results&Best Cell I-V Curve15.80.7633.76194245Average16.40.7734.26254245Best cell(%)FF(%)Jsc(mA/cm2)Voc(mV)Area(cm2)W(m)Cell name 0.005.0010.0015.0020.0025.0030.0035.0040.000.000.100.200.300.400.500.600.70Voltage(V)Current Density(mA/cm2)2007 SNEC International Solar&PV ConferenceCell Results&Best Cell I-V Curve15.80.7633.76194245Average16.40.7734.26254245Best cell(%)FF(%)Jsc(mA/cm2)Voc(mV)Area(cm2)W(m)Cell name 0.005.0010.0015.0020.0025.0030.0035.0040.000.000.100.200.300.400.500.600.70Voltage(V)Current Density(mA/cm2)2007 SNEC International Solar&PV ConferenceQuantum Efficiency of the Best Cell 2007 SNEC International Solar&PV ConferenceLaser cutting and chemical etching suitable for stencil fabricationBoth single-&double-level structured stencils have been fabricated.Double-level stencils allow grid patterns to be printed with high quality in one step.Finger profiles of 50-m wide and 22-m high,in grooves,have been demonstratedA novel alignment method enables selective emitter cell structure,with good matchingBest solar cell has a fill factor of 0.77 and efficiency of 16.4%with excellent IQE at short wavelengths(1 ohm-cm,CZ,textured)C2007 SNEC International Solar&PV ConferenceThanks for your attentionYingli SolarDriving the Future
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