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Ophir‐SpiriconLLCPage1
LasersandSolarCellManufacturing
ByDickRieley,SalesManager,MidAltanticandSoutheastRegions,Ophir‐SpiriconLLC
TheGreenmovementisencouragingtheuseofenergyefficienttechnologiessuchassolarcells.Thistechnologyhasbeenmetwithresistanceduetoitsslowreturnoninvestment.Thisiscoupledwiththe
challengeoftheefficiencyofthematerialused.Reducingthecostofmanufacturingsolarcellsislargelyinfluencedbyproductionefficienciesaswellasthetypeofphotovoltaicmaterialsused.Manufacturingefficiencieshavebeenaddressedthroughhighspeed,nearlyfullyautomatedproductionprocessesfrom
handlingofthepanels,depositionofmaterials,tofinalpackaging.Theuseofcosteffectivephotovoltaicmaterials,however,representsarealdilemma.Thelowercostdepositionmaterialsarelessefficient,whereasthehigherefficiencymaterialscostmoreandcanpossesscarcinogenicelementsthatare
federallycontrolled.
Thesolarcellmanufacturingcommunity,althoughaddressingmoreefficientandenvironmentallysafe
materials,hasconcentratedonreducingcoststhroughautomatedprocesses.Thisrequiresmethodsthatareconsistentandreliable.Theriskoftheseoperations,however,isthattheycanproducealarge
quantityoflowcost,highqualitymaterialor,justasquickly,theycanproducesubstandardpanels.
Oneaspectofthemanufacturingprocessthatiscriticalisthescribingofthephotovoltaicmaterialontheindividualcellsonthelargepanels.Lasershaveproventobehighlyreliable,consistent,and
Ophir‐SpiriconLLCPage2
predictableintheirproductionresults.Inthishighspeedmanufacturingarena,laserscaneasilykeepupwithproduction,aresilenttouse,andtypicallycontributetoacleanmanufacturingenvironment.
LaserBeamDiagnostics
However,withallthatlasershavetoofferandtheadvantagestheycanprovide,laserbeamdiagnostics
areanessentialpartoftheprocess,apartthatisoftenoverlooked.Therearetwokeydiagnosticmeasurementsthatareneededtoensurelaserconsistencyfrompaneltopanel:1)laserbeampower,and2)laserbeamdiagnostic‐size,shape,andintensity.
LaserPower:Thefirstmeasurement‐monitortheoutputpowerofthelaserusingaNISTcalibrated,
laserpowermeter.Regardlessofthequalityofthelaserbeam,ifthepowerisbelowspecification,thescribingprocesswillberejected.AsmostlaserscribersoperateatKHzrates,measuringaveragepowerissufficient.Thelaserpowerdetectorshouldhaveanactiveareatwicethesizeofthelaserbeam,with
adynamicmeasurementrangefrom100mWto100W,includingtheNISTcalibrationatthespecificoperationalwavelengthoftheprocess–typically1064nm,or532nm.Laserpower,whenmeasuredonaregularbasis,willprovideabenchmarkofprocessstabilityanduniformity.
WhenalaserpowermeteristiedintothemanufacturinglaserconsolusingUSB,automaticandperiodicmeasurementscanbetakenwithpass/failcriteriaestablishedforimmediatenotificationofameasurementoutofspecification.
LaserBeamDiagnostics:Alongwithlaserpower,thespatialinformationonthelaserbeamisequally
importanttomeasureandcontrol.Laserbeamdiagnosticstypicallyinvolvethreemeasurements;thelaserbeamsize,shape,andintensity.Intheproductionofsolarcells,thelaserbeamisusedtoscribe(ablate)thedepositedlayersofphotovoltaicmaterialdowntothebaseglass,therebyestablishingthe
individualelectricalcircuitcellsonthepanel.Withacontrolledbaselineofspatialmeasurements,theprocesscanbecontrolledwithoutallowingdeviationsinthelaserbeamthatcouldallowresidualmaterialinthescribeareapotentiallycausinganelectricalshortintheoverallpanelcircuit,resultingina
defectivepanel.
Themosttypicalmeasurementsthataremostinformativeforprocesscontrolinclude:
1)Thesizeofthelaserbeam.Theindustrystandardforbeammeasurementis13.5%ofPeak(1/e2).Thisisusefulasthecalculationisbasedonthepeakofthebeamwheretheprocessofablationis
performedandlesssoonthewingsofthebeam.
Ophir‐SpiriconLLCPage3
2)Theelipticity(roundness)ofthelaserbeam.Shouldthebeamelipticitychangefromroundtoout‐of‐roundthentheablationpatternwillchangeandtheuniformityofthescribelineswillnotbeconsistent,
producingofout‐of‐specpanels.
3)Shapeoftheoverallbeam.Thiscanaffectthesizeandeffectivenessoftheablationpatternontheglasspanel.Theabovepictureisa3D/2DimageofatypicalTopHatBeamwheretheenergyisuniform
acrossthetopportionofthebeampattern.Thisisquiteusefulinpreparingauniformscribeofacertainwidthanddepth.Dependingupontheprocess,aGaussianBeampatternmaybecalledforaswell.IneithercaseabeamdiagnosticmeasurementthatcomparestheTopHatorGaussianshapetoanidealfit
isaveryinformativevalue.Trackingthesevaluestomonitorchangeisessentialforcloseandtightprocesscontrolofthesolarcelllaserprocess.
Ophir‐SpiriconLLC
http://www.ophiropt.com/photonics