Solar Technology by Sandrio Elim SCI 322U – Energy and Society II Portland State University – Summer 2003 Thursday, July 17, 2003

Outline History Available Technology New Methods New Materials Conclusion

History - Timeline 1700 Solar furnace by Antoine Lavoisier 1839 Photoelectric effect by Antoine Cesar Becquerel 1883 First solar electric module by Charles Fritts 1905 Light behaves like particle by Albert Einstein 1915 Robert Millikan proved that Albert Einstein was right 1918 Method to grow silicon by Dr. Jan Czochralski 1941 ~ Russell Ohl invented a silicon solar cell

Available Types Monocrystalline Silicon Polycrystalline Silicon Amorphous Silicon

Monocrystalline Silicon are 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 Silicon are 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 Silicon are 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 Type Efficiency in Lab Efficiency in Production Monocrystalline 24 14-17 Polycrystalline 18 13-15 Amorphous 13 5-7 Source: Solar Server.de

New Methods Surface Structuring Tandem Cell Concentrator Cell Gratzel Cell MIS Inversion Layer Cell Lower cost substrate

New Methods – Surface Structuring Construction 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 Structuring Product of Kyosemi Co. Single cell diameter = 1.8 mm Measurement temp: 25ºC Voc = 0.578 V Isc = 0.698 mA Vpm = 0.482 V Ipm = 0.666 mA Pmax = 0.321 mW/cm2  3.21 kW/m2

New Methods – Surface Structuring Here 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 Cell Different 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 Cell Source: Triple Junction Technology.

New Methods – Tandem Cell Source: Triple Junction Technology

New Methods – Concentrator Cell A 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 Cell Electrochemical 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 Layer The 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 Substrate Still using Silicon wafer based Thickness around 10-30 microns This is 10 times thinner than current wafers Processed in lower temperature Needs 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 Materials Copper indium diselenide CuInSe2 Cadmium Telluride CdTe

New Materials – CuInSe2 Bandgap of 1 eV Voc < 0.5 V Bandgap is 0.5 eV less than required for a single junction With additional gallium Ga, increases bandgap to 1.2 eV which leads efficiency to more than 15% Still not stable due to high processing temperature Planned to increase its bandgap to 1.4 and 1.6 eV by adding more Ga and/or S as additional alloy element Source: Dünnschicht-Solarzellen

New Materials - Cadmium Telluride CdTe Unstable commonly because of rear contact Cu-doped on rear contact High processing temperature Concerns about uniformity or large area, and robustness of the process Current efficiency ranges from 12% to more than 14% Too much losses in Voc Causes to have less Jsc Theoretical maximum levels of efficiency of solar cells at standard condition. Source: Solar Energy Ireland Source: Asarco Specialty Metals

Conclusion Inventor of first solar module is Charless Fritts Types of solar cells with current technology: monocrystalline, polycrystalline, and amorphous silicon New methods: surface structuring, tandem cell, concentrator cell, Gratzel cell, MIS inversion layer, lower cost substrate New Materials: copper indium diselenide, and cadmium telluride

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