Solar TechnologybySandrio ElimSCI 322U Energy and Society IIPortland State University Summer 2003

Thursday, July 17, 2003

OutlineHistoryAvailable TechnologyNew MethodsNew MaterialsConclusion

History - Timeline

Available TypesMonocrystalline SiliconPolycrystalline SiliconAmorphous Silicon

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

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

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

Silicon Crystals Comparison Source: Solar Server.de

New MethodsSurface StructuringTandem CellConcentrator CellGratzel CellMIS Inversion Layer CellLower cost substrate

New Methods Surface StructuringConstruction of the cell surface in a pyramid or spherical structure, so that incoming light hits the surface several times. Source: Kyosemi Company Japan.

New Methods Surface StructuringProduct of Kyosemi Co.Single cell diameter = 1.8 mmMeasurement temp: 25CVoc = 0.578 VIsc = 0.698 mAVpm = 0.482 VIpm = 0.666 mAPmax = 0.321 mW/cm2 3.21 kW/m2

New Methods Surface StructuringHere is the pyramid surface structuring with a lower cost this cell will allow efficiency of over 20%.Source: Key Center for PV Engineering - UNSW

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

New Methods Tandem CellSource: Triple Junction Technology.

New Methods Tandem CellSource: Triple Junction Technology

New Methods Concentrator CellA higher light intensity will be focused on the solar cells by the use of mirror and lens systems. This system tracks the sun, and always using direct radiation.

New Methods Gratzel CellElectrochemical liquid cells with titanium oxide as electrolytes and dye to improve light absorption.Source: University of Queensland Soft Condensed Matter Physics

New Methods MIS Inversion LayerThe inner electrical field are not produced by a p-n junction, but by the junction of a thin oxide layer to a semiconductor.

New Methods Lower Cost SubstrateStill using Silicon wafer basedThickness around 10-30 micronsThis is 10 times thinner than current wafersProcessed in lower temperatureNeeds light trapping because:- Impurity interaction with the foreign substrate- Partly due to imperfect crystallinity and structural defects.Solution to have light trapping feature is to have Si films with large grain size.

New MaterialsCopper indium diselenide CuInSe2Cadmium Telluride CdTe

New Materials CuInSe2Bandgap of 1 eVVoc < 0.5 VBandgap is 0.5 eV less than required for a single junctionWith additional gallium Ga, increases bandgap to 1.2 eV which leads efficiency to more than 15%Still not stable due to high processing temperaturePlanned to increase its bandgap to 1.4 and 1.6 eV by adding more Ga and/or S as additional alloy elementSource: Dnnschicht-Solarzellen

New Materials - Cadmium Telluride CdTeTheoretical maximum levels of efficiency of solar cells at standard condition.Source: Solar Energy IrelandSource: Asarco Specialty MetalsUnstable commonly because of rear contactCu-doped on rear contactHigh processing temperatureConcerns about uniformity or large area, and robustness of the processCurrent efficiency ranges from 12% to more than 14%Too much losses in VocCauses to have less Jsc

ConclusionInventor of first solar module is Charless FrittsTypes of solar cells with current technology: monocrystalline, polycrystalline, and amorphous siliconNew methods: surface structuring, tandem cell, concentrator cell, Gratzel cell, MIS inversion layer, lower cost substrateNew Materials: copper indium diselenide, and cadmium telluride

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