Solar TechnologySolar Technology

bybySandrio ElimSandrio ElimSCI 322U – Energy and Society IISCI 322U – Energy and Society IIPortland State University – Summer 2003Portland State University – Summer 2003

Thursday, July 17, 2003Thursday, July 17, 2003

22

OutlineOutline

HistoryHistory Available Available

TechnologyTechnology New MethodsNew Methods New MaterialsNew Materials ConclusionConclusion

33

History - TimelineHistory - Timeline

17001700 Solar furnace by Antoine LavoisierSolar furnace by Antoine Lavoisier

18391839 Photoelectric effect by Antoine Cesar BecquerelPhotoelectric effect by Antoine Cesar Becquerel

18831883 First solar electric module by Charles FrittsFirst solar electric module by Charles Fritts

19051905 Light behaves like particle by Albert EinsteinLight behaves like particle by Albert Einstein

19151915 Robert Millikan proved that Albert Einstein was Robert Millikan proved that Albert Einstein was rightright

19181918 Method to grow silicon by Dr. Jan CzochralskiMethod to grow silicon by Dr. Jan Czochralski

1941 1941 ~~

Russell Ohl invented a silicon solar cellRussell Ohl invented a silicon solar cell

44

Available TypesAvailable Types

Monocrystalline SiliconMonocrystalline Silicon Polycrystalline SiliconPolycrystalline Silicon Amorphous SiliconAmorphous Silicon

55

Monocrystalline SiliconMonocrystalline Silicon

are made of silicon wavers are made of silicon wavers cut from one homogenous cut from one homogenous crystal in which all silicon crystal in which all silicon atoms are arranged in the atoms are arranged in the same direction. The same direction. The monocrystal is monocrystal is manufactured using the manufactured using the "CZOCHRALSKI GROWTH "CZOCHRALSKI GROWTH TECHNOLOGY". Hereby a TECHNOLOGY". Hereby a round bar of silicon is round bar of silicon is drawn with a speed of a drawn with a speed of a few centimeters per hour few centimeters per hour from pure molten silicon. from pure molten silicon.

Source: Wafertech

66

Polycrystalline SiliconPolycrystalline Silicon

are poured and are are poured and are cheaper and simpler to cheaper and simpler to make than monocrystalline make than monocrystalline silicon. Whilst setting the silicon. Whilst setting the different crystals are different crystals are formed that give the formed that give the material its characteristic material its characteristic flaky blue metallic color. flaky blue metallic color. The efficiency of The efficiency of multicrystalline cells is multicrystalline cells is however somewhat less however somewhat less than that of than that of monocrystalline cells. monocrystalline cells.

Source: Kyocera Co. Japan

77

Amorphous SiliconAmorphous Silicon

are made with help of a are made with help of a deposition technique, like deposition technique, like plasma deposition. These plasma deposition. These are called amorphous are called amorphous silicon Cells, which are silicon Cells, which are relatively cheap, but with relatively cheap, but with low efficiency. low efficiency. "AMORPHOUS" means: No "AMORPHOUS" means: No crystalline structure. III/V crystalline structure. III/V solar cells are cells with a solar cells are cells with a high efficiency, but are high efficiency, but are made of very expensive made of very expensive semi-conducting materials. semi-conducting materials. Furthermore there are Furthermore there are various types of thin film various types of thin film polycrystalline cells and polycrystalline cells and cheap organic cells. cheap organic cells.

Source: GFa - Visolar

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Silicon Crystals Silicon Crystals Comparison Comparison TypeType Efficiency in Efficiency in

LabLabEfficiency in Efficiency in ProductionProduction

MonocrystallinMonocrystallinee

2424 14-1714-17

PolycrystallinePolycrystalline 1818 13-1513-15

AmorphousAmorphous 1313 5-75-7Source: Solar Server.de

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New MethodsNew Methods

Surface StructuringSurface Structuring Tandem CellTandem Cell Concentrator CellConcentrator Cell Gratzel CellGratzel Cell MIS Inversion Layer MIS Inversion Layer

CellCell Lower cost substrateLower cost substrate

1010

New Methods – Surface New Methods – Surface StructuringStructuring Construction of the cell Construction of the cell

surface in a pyramid or surface in a pyramid or spherical structure, so spherical structure, so that incoming light hits that incoming light hits the surface several the surface several times. times.

Source: Kyosemi Company Japan.

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New Methods – Surface New Methods – Surface StructuringStructuringProduct of Kyosemi Co.Product of Kyosemi Co.

Single cell diameter = 1.8 mmSingle cell diameter = 1.8 mm

Measurement temp: 25ºCMeasurement temp: 25ºC

Voc = 0.578 VVoc = 0.578 V

Isc = 0.698 mAIsc = 0.698 mA

Vpm = 0.482 VVpm = 0.482 V

Ipm = 0.666 mAIpm = 0.666 mA

Pmax = 0.321 mW/cmPmax = 0.321 mW/cm2 2 3.21 kW/m 3.21 kW/m22

1212

New Methods – Surface New Methods – Surface StructuringStructuring Here is the Here is the

pyramid surface pyramid surface structuring with a structuring with a lower cost this lower cost this cell will allow cell will allow efficiency of over efficiency of over 20%.20%.

Source: Key Center for PV Engineering - UNSW

1313

New Methods – New Methods – Tandem CellTandem Cell Different semiconductor Different semiconductor

materials will be arranged materials will be arranged one on top of the other to one on top of the other to decrease the amount of decrease the amount of energy lost during energy lost during absorption. The cells are absorption. The cells are arranged so that they are arranged so that they are in descending order in in descending order in terms of band gap (Eg).terms of band gap (Eg). Source: National

Renewable Energy Laboratory

1414

New Methods – New Methods – Tandem CellTandem Cell

Source: Triple Junction Technology.

1515

New Methods – New Methods – Tandem CellTandem Cell

Source: Triple Junction Technology

1616

New Methods – New Methods – Concentrator CellConcentrator Cell A higher light intensity will be focused A higher light intensity will be focused

on the solar cells by the use of mirror on the solar cells by the use of mirror and lens systems. This system tracks and lens systems. This system tracks the sun, and always using direct the sun, and always using direct radiation.radiation.

1717

New Methods – Gratzel New Methods – Gratzel CellCell Electrochemical Electrochemical

liquid cells with liquid cells with titanium oxide as titanium oxide as electrolytes and electrolytes and dye to improve dye to improve light absorption.light absorption.

Source: University of Queensland – Soft Condensed Matter Physics

1818

New Methods – MIS New Methods – MIS Inversion LayerInversion Layer

The inner electrical field are not The inner electrical field are not produced by a p-n junction, but produced by a p-n junction, but by the junction of a thin oxide by the junction of a thin oxide layer to a semiconductor.layer to a semiconductor.

1919

New Methods – Lower New Methods – Lower Cost SubstrateCost Substrate Still using Silicon wafer basedStill using Silicon wafer based Thickness around 10-30 micronsThickness around 10-30 microns This is 10 times thinner than current wafersThis is 10 times thinner than current wafers Processed in lower temperatureProcessed in lower temperature Needs light trapping because:Needs light trapping because:

- Impurity interaction with the foreign - Impurity interaction with the foreign substratesubstrate- Partly due to imperfect crystallinity and - Partly due to imperfect crystallinity and structural defects.structural defects.

Solution to have light trapping feature is to Solution to have light trapping feature is to have Si films with large grain size.have Si films with large grain size.

2020

New MaterialsNew Materials

Copper indium diselenide CuInSeCopper indium diselenide CuInSe22

Cadmium Telluride CdTeCadmium Telluride CdTe

2121

New Materials – New Materials – CuInSeCuInSe22

Bandgap of 1 eVBandgap of 1 eV Voc < 0.5 VVoc < 0.5 V Bandgap is 0.5 eV less than required Bandgap is 0.5 eV less than required

for a single junctionfor a single junction With additional gallium Ga, increases With additional gallium Ga, increases

bandgap to 1.2 eV which leads bandgap to 1.2 eV which leads efficiency to more than 15%efficiency to more than 15%

Still not stable due to high processing Still not stable due to high processing temperaturetemperature

Planned to increase its bandgap to 1.4 Planned to increase its bandgap to 1.4 and 1.6 eV by adding more Ga and/or and 1.6 eV by adding more Ga and/or S as additional alloy elementS as additional alloy element

Source: Dünnschicht-Solarzellen

2222

New Materials - New Materials - Cadmium Telluride Cadmium Telluride CdTeCdTe

Theoretical maximum levels of efficiency of solar cells at standard condition.Source: Solar Energy Ireland

Source: Asarco Specialty Metals

Unstable commonly because of rear Unstable commonly because of rear contactcontact

Cu-doped on rear contactCu-doped on rear contact High processing temperatureHigh processing temperature Concerns about uniformity or large Concerns about uniformity or large

area, and robustness of the processarea, and robustness of the process Current efficiency ranges from 12% to Current efficiency ranges from 12% to

more than 14%more than 14% Too much losses in VocToo much losses in Voc Causes to have less JscCauses to have less Jsc

2323

ConclusionConclusion

Inventor of first solar module is Inventor of first solar module is Charless FrittsCharless Fritts

Types of solar cells with current Types of solar cells with current technology: monocrystalline, technology: monocrystalline, polycrystalline, and amorphous siliconpolycrystalline, and amorphous silicon

New methods: surface structuring, New methods: surface structuring, tandem cell, concentrator cell, Gratzel tandem cell, concentrator cell, Gratzel cell, MIS inversion layer, lower cost cell, MIS inversion layer, lower cost substratesubstrate

New Materials: copper indium New Materials: copper indium diselenide, and cadmium telluridediselenide, and cadmium telluride

2424

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