Solar Energy Materials And Solar Cells | Types Of Solar Cells

Solar radiation received on earth in just one hour is more than what the whole world’s population consumes in one year. 3,850,000 Exajoules (EJ) amount of solar energy received by Earth Surface per year. In 2011, worldwide primary energy consumptions was 550 EJ. 7 hours of Solar Energy at Deserts can meet annual global energy requirement.

Note: 1 EJ = 10 ¹⁸ J

(i.e in the order, Joule (J), Kilo Joule, Mega joule, Giga Joule, Tera Joule, Peta Joule, Exa Joule, Zeeta Joule, Yotta Joule and so on.)

What is Photovoltaics (“PV”)?

• Photovoltaic (phōs) = light (@ Greek )and “voltaic” = electric (from Volta, Italian physicist)
• Conversion of sun light directly into electricity through semi conductor materials
• Electricity for 2 billion people around the world

What is Photovoltaic (PV) systems?

A PV system consist of:

• Photovoltaic cells connected into modules and encapsulated Modules grouped into panels.
• Panels groups into arrays,
• A power conditioning unit,
• Batteries.

History of Photovoltaic’s:

In 1839, a young French physicist named Edmund Bacquerel discovered the photovoltaic effect. While working with two metal electrodes in an electricity-conducting solution, he noted that the apparatus generates voltage when exposed to light.

When 1904, Albert Einstein published a paper on the photoelectric effect, that the general scientific community stopped looking at photovoltaic as some type of scientific hoax.

1839        Becquerel:             Photogalvanic effiect

1873        Smith:                    Photoconductivity of Se

1883        Fritts:                     Se films solar cells

1946        Russel Ohl             Modern Solar cell Patent

1954        Bell Lab:                 6% Si solar cells

1959        Hoffman:               2% Si cells (industrial)

1966        NASA:                    1kW array

1974        Sunshine:              Alternatives to Si

1980                                       Thin-film 10% Cu₂S/CdS

1985                                       High Efficiency 20%; Conc. 25% (Si)

1999                                       1GW installed (cumulative)

2007                                       ~3GW

2008                                       Sunpower 18.5% PV panel

2009                                       Low cost (<1$/wp) module by First solar

Note: Se – Selenide, Si – Silicon, CdS- Cadmium Sulfides, Cu₂S- Copper Sulfides.

What is Solar Cell?

The basic component of a PV system is solar cell.

Two fundamental functions:

1. Photo-generation of charge carriers (electrons and holes) in a light-absorbing material
2. Separation of the charge carriers to a conductive contact to transmit electricity

If light with adequate energy falls onto silicon arranged to form a p-n junction and penetrates to a point near the junction, then, because of the photo-electric effect, it will create free electrons near the junction. These electrons immediately move under the influence of the p-n junction’s electric field. The electrons continue to move through the cell to the surface of the cell. On the way towards the surface of the cell some of the electrons may be re-absorbed by the silicon atoms, but many electrons still reach the surface of the cell. These electrons can be collected by a metallic grid and an electric current will flow if the grid is connected to the metal contact on the other side of the cell by an external circuit.

Photovoltaic Materials:

• Crystalline silicon (c-Si)
• Amorphous silicon (s-si)
• Cadmium Telluride (CdTe)
• Copper Indium Diselenide (CIS)
• III-V Family (Gallium arsenide….)
• Dye-Sensitised Solar Cells (DSSC)
• Organic Photovoltaics (OPV)