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1、BOOMERANG·TRANSACTIONSSpectroscopyofSolarCellsN.J.Ekins-Daukes,M.Guenette∗SchoolofPhysics,UniversityofSydney,NSW2006,Australia(Dated:May15,2006)Theoperationofasolarcelllendsitselftospectroscopicanalysis.Itisshownthatasolarcellcanbeunderstoodatthefundamentallevelsimplythrou
2、ghageneralisedPlanckformalism,allowingfundamentallimitstobeplacedontheefficiencyofasolarcell.Importantly,thisapproachalsoallowsspectraobtainedfromsolarcellstobeinterpreted,providinganinsightintothefundamentaloperationofsolarcelldevices.I.INTRODUCTIONPhotovoltaicsolarcellscon
3、vertsunlightintoelectricityandeffectivelyoperateaselectronicheatengines.Inmostelectronicdevices,itisnotnecessarytoconsidertheun-derlyingthermodynamicsofthedevicetoappreciatetheprincipleofoperation,andthesubjectisoftenomittedentirelyfromsemiconductorphysicstexts.Nevertheless
4、,byconsideringthethermodynamicsofasolarcell,itispossibletoshowthatasolarcell,lightemittingdiodeandphotodetectorareessentiallythesamedevice,operatingindifferentthermodynamicregimes.Inthisarticletheprinciplesofsolarenergyconversionarebrieflyreviewed,withaparticularemphasisonho
5、wspectroscopyprovidesaninsighttotheoperationofasolarcell.MostenergysourcesonEarthcanbetracedbacktothesun.ThesolarpowerdensityinEarthorbitisap-proximately1350W/m2[1],droppingtoapproximately1000W/m2afterabsorptionthroughtheEarth’satmo-FIG.1:Solarspectralirradiance,showingthe
6、extraterrestrialsphere[2].Figure1comparestheextraterrestrial,airAM0andterrestrialstandardAM1.5G.mass0(AM0)solarspectrumagainstthestandardAM1.5globalspectrum,indicatingthattheatmosphereismainlytransparentatvisiblewavelengths,buthasre-gionsofsignificantabsorptionintheinfrared
7、.Theex-2.16×10−5[4].TheassociatedenergyfluxisgivenbytheR∞traterrestrialsolarspectrumcloselyresemblestheemis-integralEn(E)dEandisequivalenttotheStefan-0sionofablackbodyat6000Kandcanbeaccuratelymod-4Boltzmannlaw,σTwhereσistheStefan-BoltzmannelledusingageneralisedformofthePlan
8、ckequation[3]:constant.Themostgeneralformofsolarenergyconvertoris2πE2showninfigure2.Anabso