An Overview of Solar Cell Technology

1 An Overview of Solar Cell TechnologyMike McGeheeMaterials Science and EngineeringGlobal Climate and Energy ProjectGlobal Climate and Energy ProjectCenter for Advanced Molecular PhotovoltaicsPrecourt InstituteStanford UniversityKonarkaNanosolarJohn Benner provided the slides with the NREL Photovoltaic (PV) MarketsResidential RooftopCommercial RooftopGround mounted (Usually 2utility scale)How cheap does PV need to be to compete w/ coal?June 2008 Installed System Price per Watt, 2008-20113Q10 Breakout$ $ $ $ Renewable Energy Laboratory Innovation for Our Energy FutureOriginal Source: Deutsche Bank, January 2011; Systems are global ( , blended across geographies)My source: R.

2 Swanson, IEEE PV Specialists Conf., June 20114PV is a booming industry, especially in China5 But not everyone prospered in 2011 Solyndra SpectraWatt and Evergreen Solar went bankruptJon Stewart, The Daily ShowSolyndra, SpectraWatt and Evergreen Solar went makes the PV industry so it ti ?interesting? PV addresses the energy problem which many passionately PV addresses the energy problem, which many passionately want to solve. By 2050 the world will need~30 TW of 2050 the world will need 30 TW of power. Some think PV could provide 20 % of that. It takes a panel rated at 5 W, to average 1 W of power through the day and year, so gp gyywe would need 30 TW of PV capacity.

3 At $1/W, the industry would take in $30 trillion. The industry is now well over $40 are many approaches to making PV cells and experts do not agree on which one is the bestand experts do not agree on which one is the bestSi180 National Renewable Energy Laboratory Innovation for Our Energy Future20x-100x500xCu(In,Ga)Se2 ~ 1-2 umc-Si ~ 180 umLots of records in 2011!More factors that make the plot pinteresting The overall global economy has been turbulent for a few years. Government policies are constantly policies are constantly changing.

4 When an industry based on manufacturing grows faster than 40 %/year in spurts, it is hard for the supply chain to always provide ypppyypwhat is p-n junction photovoltaic ( Solar ) cellEffi ili itThermalization of excess energySources of energy lossEfficiency limitsBelow band gap photons not absorbedexcess energyCBVBI ncreasing VOCand decreasing JSCM ultijunctions: The Road to Higher EfficienciesHigher-efficiency MJ cells require new materials that divide the Solar spectrum equally to provide current matchGe provides lattice match but the bandgap is too eVNew Solar JiISC2009 Tokyo University, March 3, 2009 JSH 13p4567891234 Energy (eV)Junction MJ CellConventionalMJ CellSolar Junction World RecordWorld s most efficient Solar cellsolar cell ever 418-655 suns418-655 suns14 PROPRIETARY AND CONFIDENTIAL.

5 PROPERTY OF Solar JUNCTION. PROPRIETARY AND CONFIDENTIAL. PROPERTY OF Solar JUNCTION. 2010 Production by Cell TypeNational Renewable Energy Laboratory Innovation for Our Energy FutureSource: PV News, May 2011 Silicon PVSilicon FeedstockIngot GrowthSlicing WafersCell FabricationModule EncapsulationPhotovoltaic SystemNational Renewable Energy Laboratory Innovation for Our Energy FutureSimple Cell Technologies continue to improve- efficient planar cells on CZ siliconNational Renewable Energy Laboratory Innovation for Our Energy FutureSource.

6 J-H Lai, IEEE PVSC, June 2011 In September 2011 there were protests at a Chinese PV factory over pollution in the riverChemical and Engineering News, September 26, 2011 #CHINAA fter this presentation was given, a article with a response from Suntech was published at on Silicon PVConclusions on Silicon PV Progress has been better than many expected. Modules are being sold at $1/W, but not for profit. $1/W w/ profit seems inevitable. It is not yet clear that $ Si cells can be made Film Solar Cells A thin film of semiconductor is deposited by low cost methods. Less material is used Less material is used.

7 Cells can be flexible and integrated directly into roofing CdS P-type CdTe3~8 umGlass SuperstrateTransparent Conducting Oxide um~1000 umCdTeCdTeSolar Cell withSolar Cell withCdSCdSwindow layerwindow layerCdTeCdTeSolar Cell with Solar Cell with CdSCdSwindow layerwindow layerMetalBack Contact: CathodeP-type CdTeMetalAbsorber layer3~8 umTransparent Conducting Oxide N-type CdS Window umGlass SuperstrateFront Contact: Anode~1000 umIncident Light22 CdS: tends to be n-type, large bandgap( ) Cadmium Telluride Solar CellsCadmium Telluride Solar Cellsglass Direct bandgap, Eg= d ffi i(Rd173%) Good efficiency ( ) High module production speed Long term stability (20 years)CdS/CdTeImage from Rommel NoufiSchematic from Bulent BasolCdTe: Industrial StatusCdTe: Industrial StatusFirst Solar is the leader.

8 It takes them hours to make a 11 % Manufacturing Cost 2006: $ $1 23/tt2007: $ : $ : $ : $ energy payback time is p yyOne reason cells on the roof don t have 17 3 % % efficiencyThh lli i d t i t ilt thi CdS litht h i25 From Reuben CollinsThe challenge in industry is to implement thin CdS layers without having a much of a problem is the toxicity of Cd?It is probably manageable First Solar will recycle theIt is probably manageable. First Solar will recycle the panels when the customer is done with (InGa1)Se2Cu(InxGa1 x)Se2 World record efficiency = %.

9 Many companies are evaporating, printing, sputtering and electrodepositing it. Some are manufacturing ~30-50 MW/yr. Handling a 4-element compound is toughHandling a 4element compound is Solar , CAGlobal Solar Energy AZGlobal Solar Energy, AZEnergy Photovoltaics, NJISET, CAITN/ES, COWurth Solar , GermanySULFURCELL, GermanyNanoSolar Inc., CADayStar Technologies, NY/CAMiaSole, CAHelioVolt Tx,yCIS Solartechnik, GermanySolarion, GermanySolibro, SwedenCISEL FranceHelioVolt, TxSolyndra, CASoloPower, CACISEL, FranceShowa Shell, JapanHonda, JapanSolyndra s CIGS comparison of Solyndra s modules to their to Avoid HeatingPlease view the videos on their website to see the manufacturing and installation went wrong?

10 There are significant disadvantages to using cylinders ( more area more dark current)area, more dark current). Just about everything in the factory had to be custom built to enable the use of The glass cylinders are not as cheap as those used in fluorescent light tubes. The price of crystalline silicon dropped faster than Solyndra expected. Building a second factory wasn t a great Roscheisen explained the disadvantages of the Solyndra approachMartin Roscheisen explained the disadvantages of the Solyndra approach back in 2009. ( ) s Roll-to-Roll CoatingSee videos of the coating machine and module packaging on Nanosolar s is a 16-page white paper on the Nanosolar website describing this s Cell and Module DesignMiasol Miasol Sputters CIGS on steel foil % efficient modules verified by NRELF llttdfkidl Fully automated process for making modules Should be shipping ~ % efficient modules at around $ soonIs there enough Te for CdTe?