多孔硅在太阳电池中应用有着很大的 潜力。
R.Bilyalovetal./SolarEnergyMaterials&SolarCells65(2001)477}485483
withadi!useentranceofthelight,(2)thestackedporouslayershouldnotresultinanexcessivelightabsorption,and"nally(3)thepore"llinge!ectshouldbeavoidedbecausethismightleadtoauniformlyloweredremainingporosity.
3.4.Solarcells
Our"rstattempttorealizeathin-"lmsolarcellonaPSbarrierlayerwasdonebygrowinganepitaxialSilayerat8003Conthe60%singlePSlayer[3].However,thisresultedinahighlydefectedSi-layer.Wehavemodi"edtherealizationpreparationoftheSi/PS/SubstratestructureasdescribedbelowinordertoimprovethequalityoftheSi"lmdepositedonthePSlayer.
TheCVD-processisinitiatedusingDCSat7253CandisappliedonadualPShavingatoplayerporosityofonly20%.Thisallowsthedepositionofahigh-qualityepi-layerwithalowdefectdensity((10 cm\ )asdiscussedpreviously(Fig.1).Afterthegrowthofthishigh-qualitytemplatelayerwithanapproximatethicknessof500nm,theCVD-processiscontinuedat8003Cinordertohaveasu$cientlyhighgrowthrate.Subsequently,ahomogeneouslydopedp>-Si(contactinglayer,1 m\ ;10 cm\ )andp-Si(base,3.5 m\ ;10 cm\ )layeraregrown.Thesamedepositionhasbeenappliedonamono-Siandadual(%)poroussurface.Afterwardsasn>-Siemitterisdi!usedfromPOsolidsources,aremoteplasma nitridedepositionisappliedonthefrontsurface,themesa-etchisperformedandthecontactsareappliedusingmetalevaporation.
Theadvantageofsuchamesa-cellstructureisthattheburiedporouslayerremainsintactsincenoconductingviashavetobeforeseenforthecarriercollectionatthebackside.Thisismoreappropriateinviewoftheultimateapplicationofepi-on-PSoncheaplow-qualitySi-substrates.Firstly,thebarrierlayerandgetteringactivityoftheburiedporouslayermightbedisturbedbythepresenceoftheconductingviasthatcouldallowdi!usionofimpuritiesfromthesubstratetotheSi"lm.Secondly,amesa-celloraninterdigitatedstructurehastheinherentadvantageofallowingamonolithicintegrationofthesolarcellsuptothemodulelevel.ThedataofilluminatedI}Vcharacteristicsforthesethin-"lmsolarcellsarepresentedinTable2.Arelativelylowopen-circuitvoltage(V)andanincreasedrecombinationcurrent areobservedforbothcellswithandwithoutaPSintermediatelayer.Probablythefactthatbothcellshavebeenprocessedsimultaneously(CVDgrowthandsubsequentcellprocessing)givesrisetoastronglydecreasedcarrierlifetimeandanincreasedrecombinationcurrentduetometalcontamination.IndeedCuhavingaveryhighTable2
ExtractedI}Vparametersforathin"lmsolarcellstructureonaSisubstrateandonaPSwithdual(porositystructure
Cell
Reference(epi-on-Si)
DualPS(epi-on-%PS)J(MA/cm ) 19.518.7V(mV) 336362FF(%)58.561.2E!(%)3.94.2