solarcell203-200326231350.pdf............

bnjhj

1. SOLAR CELL

2. Introduction
Powercrisisisoneofthemajorconcernsintoday’sworld.Duetodriveofthehuge
numberofmoderntechnology,thedemandoffuelisincreasingdaybyday.Atthe
sametimethenaturalsourcesarereducing.Anotherconcernofusingthisfossil
fuelistoits’detrimentaleffectonenvironmentbecauseburningofthisfuel
generatescarbon-di-oxidethatultimatelyincreasetheglobalwarmingdueto
greenhouseeffect.Therenewableenergysourceswouldbethepromising
candidateforresolvingthepowercrisisandenvironmentalconcern.
Renewableenergyistheenergythatcomefromnaturalresourceslikesunlight,
wind,tides,rain,biomass,geometrical,hydroetcthatgeneratesenergywith
renewability.Amongalltheavailablerenewableenergysources,solarenergy
gainedmuchinterestbecauseofthelimitlessavailabilityandnon-toxicity.Solar
cellsareusedforgeneratingpowerfromsolarenergy.
Solarcellsarephotovoltaic(PV)devicethatconvertstheenergyofsunlightinto
electricalpowerwithoutanychemicalreaction.Solarenergyisabundant,
inexhaustibleandclean.Itisfreefromanykindofpollution,needsnomovingparts,
consumesnofuelandrequireslittlemaintenance.

4. Solar Radiation Pattern
ALLAHHASmadethesunasoriginofhugeenergyneededfordrivingvarioussystemson
earth.Theprocessbywhichthissolarheatenergytravelsthroughspaceintheformof
electromagneticwavesisknownasradiation.Thesuncanbeconsideredasablackbody
havingatemperatureof5800Konitssurface.Thetotalenergyemittedfromthesun’s
surfaceisabout63,000,000W/m2.Itemits1.1x10e20Kw-hr/sec

5. Solarirradiance:
Thesolarenergyvariesbecauseoftherelativemotionofthesun.Thisvariationsdepend
onthetimeofdayandtheseason.Theamountsofsolarenergyarrivingattheearth's
surfacevaryovertheyear,fromanaverageoflessthan0,8kWh/m2perdayduringwinter
intheNorthofEuropetomorethan4kWh/m2perdayduringsummerinthisregion.The
differenceisdecreasingfortheregionsclosertotheequator.Irradianceisdefinedasthe
amountofelectromagneticenergyincidentonasurfaceperunittimeperunitarea.There
aredifferentwaystomeasurelight,howeverintermsofSolarandPV(photovoltaic)
technologytheequationisshownbelow:
Irradiance = Power / Area

7. ThesunalsoproducesGammaraysonitssurfaceduringthenuclearfusionprocesswhichis
convertedintoalowerenergybeforeitreachestheearth’ssurface.Italsoemitsultraviolet,
X-rays,infrared,visiblelight,radiowaves.Thespectrumofthesolarradiationisinarangeof
100nmto1mm.
UltravioletC(UVC):ithasarangeof100to280nmwavelength.Ultravioletmeansithasa
radiationathigherfrequencythanthevioletlightwhichalsoinvisibletothehumaneye.The
mostofitisabsorbedbytheatmosphere.Thusaverylittleportionofitreachesthesurface
oftheearth.
UltravioletB(UVB):Therangespansfrom280to315nmwhichisalsoabsorbedbythe
atmosphereinahugeamount.Itisresponsibleforthephotochemicalreactionleadingto
theproductionoftheozonelayer.Itisveryharmfulforthehealth.itcausessunburnand
damagesDNA.
UltravioletA(UVA):Therangeofitswavelengthspansfrom315to400nm.Thiscanalso
damageDNAandisabletocausecancerviaindirectroutes.
Visiblelight:Spansfrom380to780nm.Itisvisibletohumaneyeasitsnamesuggests.Itis
thestrongestoutputrangeofthesun’stotalirradiancespectrum.
Infrared:spansfrom700nmto1,000,000nm.Itisatypeofelectromagneticradiation
whichisinvisibletohumaneye.Onthebasisofwavelengthitcanbedividedintothree
parts:
Infrared-A:700nmto1,400nm
Infrared-B:1,400nmto3,000nm
Infrared-C:3,000nmto1mm.
Solarradiation:

8. Photo Voltaic or PV Mechanism
Photovoltaicsisthedirectconversionoflight(photon)intoelectricityattheatomic
level.Somematerialsexhibitapropertyknownasthephotoelectriceffectthat
causesthemtoabsorbphotonsoflightandreleaseelectrons.Whenthesefree
electronsarecaptured,anelectriccurrentresultsthatcanbeusedaselectricity.
ThephotoelectriceffectwasfirstnotedbyaFrenchphysicist,EdmundBequerel,in
1839,whofoundthatcertainmaterialswouldproducesmallamountsofelectric
currentwhenexposedtolight.In1905,AlbertEinsteindescribedthenatureoflight
andthephotoelectriceffectonwhichphotovoltaictechnologyisbased,forwhich
helaterwonaNobelprizeinphysics.ThefirstphotovoltaicmodulewasbuiltbyBell
Laboratoriesin1954

9. Bandgap diagram of conductor, semiconductor and Insulator

10. Conductors:Atabsolutezerotemperaturealargeamountofelectronsremainonthe
conductionband.Thevalancebandandconductionoverlapseachother.Thereisno
forbiddenenergygap.Astheresistancebeingverylow,ahugenumberofchargecarriersare
availablehere.So,electricitycanpasseasilythroughtheconductors.
Insulators:Electricitycannotpassthroughthesematerials.Thevalancebandremainsfullof
electronsandtheconductionbandremainsempty.Theforbiddenenergygapbetweenthe
conductionbandandthevalencebandiswidest.Thedifferenceismorethan10ev.Alarge
amountofenergyisneededtocrosstheforbiddenenergygap.
Semiconductors:Theelectricalconductivityisbetweenconductorsandinsulators.The
forbiddenenergygapofasemiconductorisnearlysameasinsulatorandisnarrower.The
valueofEg=1.1eVforsiliconcrystalandEg=0.7eVforgermaniumat0K.Asemiconductor
remainspartiallyfullvalencebandandpartiallyfullconductionbandattheroom
temperature.So,siliconandgermaniumareinsulatorsatabsolutezerotemperature.Onthe
otherhandwiththeincreasingoftemperaturetheelectricalconductivityofsemiconductors
increases.

11. Working Principle of Solar Cell
P-type and N-type Materials
AtomicdistributionsofSi(2+8+4);B(2+3),andP(2+8+5).Eachsiliconatomhasfour
electronsinitsvalancebandandtheseelectronsmakebondswithotherSiliconatom
Dopingprocessisneededtoobtainn-typeorp-typeSi.
Si-atom N-type Si-atom
P-type Si-atom

12. Working Principle of Solar Cell
P-NJunction:
Whenwebringp-typeandn-typematerialtogether,adiffusionoccursonthesurfacebetween
them.Electronsstartstodiffusefromn-typetop-type.Similarly,holesdiffusesfromp-type
regionton-typeregion.Thisdiffusioncreatesaelectron-holefreeregioninaveryshort
distanceattheinterfaceregion.Thisthinlayeriscalleddepletionregion.

13. Working Principle of Solar Cell
Thesolarcellisconsideredasamajorcandidateforobtainingenergyfromthesunasitcan
convertsunlightdirectlytoelectricitywithhighconversionefficiency.Itcanprovidenearly
permanentpoweratlowoperatingcost,andisalmostfreeofpollution.

14. SolarCellDeviceStructure:
Solarcellsaremainlyformedbycreatingp-njunctionsregioninsemiconductors.Figure
showsacross-sectionalschematicofatypicalsolarcell.

15. Thefirstlayeriscalledemitterlayerwhichisusuallymoreheavilydopedandthinnerthan
thebaselayer.Thebaselayeristhickerandlightlydopedandmostofthelightabsorption
happensinthislayer.Lowerdopingcauseshigherminoritycarrierlifetimeandhigher
diffusioncoefficients,whichinturnimprovesthecarrierdiffusionlength.Lowerdopingin
thebaseincreasesthedepletionregioninthebase,whichcanaidincarriercollectiondueto
theelectricfield.Ifthedopingistoolowitmayincreasethedarkcurrent,whichmay
degradetheperformance.
Solar Cell Device Structure:

16. Siliconsolarcellsareofdifferenttypes:
i)Monocrystallinesiliconsolarcell,
ii)Polycrystallinesolarcell,
iii)Amorphoussiliconsolarcell.
Types of Solar Cell
Monocrystallinesolarcells,alsocalled“singlecrystalline”cellsareconsideredtobemade
fromaverypuretypeofsilicon.Polycrystallinesolarcells,alsoknownaspolysiliconand
multi-siliconcells.Amorphoussiliconsolarcellsbelongtothecategoryofsiliconthin-film.
Theword“amorphous”literallymeansshapeless.Thesiliconmaterialisnotstructuredor
crystallizedonamolecularlevel,asmanyothertypesofsilicon-basedsolarcellsare.Itis
madebylayeringseveralphotovoltaicmaterialsdepositedontoasubstrate.

19. Appealing Characteristics
•Consumes no fuel
•No pollution
•Wide power-handling capabilities
•Solar power helps to slow/stop global warming.
•Solar power saves money.

21. Solar cell –Working Principle