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

2. Outline History Available Technology New Methods New Materials
Conclusion

3. 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

4. Available Types Monocrystalline Silicon Polycrystalline Silicon
Amorphous Silicon

5. 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

6. 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

7. 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

8. 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

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

10. 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.

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

12. 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

13. 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

14. New Methods – Tandem Cell
Source: Triple Junction Technology.

15. New Methods – Tandem Cell
Source: Triple Junction Technology

16. 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.

17. 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

18. 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.

19. New Methods – Lower Cost Substrate
Still using Silicon wafer based
Thickness around 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.

20. New Materials
Copper indium diselenide CuInSe2
Cadmium Telluride CdTe

21. 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

22. 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

23. 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

24. Bibliography http://cope.org.nz/sunpower/apres/custom.htm
nitrogen-solar-cell.html
info/bcsc.html
gateway/ee/solar/solar.html
growth.html