Solar Cell, from Past to Present

The recorded development of solar cell technology begins with the 1839 research of French experimental physicist Antoine-Edmond Becquerel. At the age of nineteen he discovered the photovoltaic effect while experimenting with an electrolytic cell containing two metal electrodes. He found that certain metals and solutions would produce small amounts of electric current when exposed to light. In 1883 Charles Fritts formed photovoltaic junctions by coating selenium with an extremely thin layer of gold. Russell Ohl invented the first silicon solar cell in 1941.

The era of modern solar cell technology began in 1954, when G. L. Pearson, D. Shapin and C. Fuller demonstrated a silicon solar cell capable of 6% energy conversion efficiency with direct sunlight. The first gallium arsenide (GaAs) solar cell was reported in 1956, with a photoconversion efficiency of 6.5%. In 1976 Carlson and Wronksi reported solar cells comprised of amorphous silicon.

Modern multi-junction solar cells can be viewed as a series of p-n junction photodiodes, each of different bandgap, that commonly include such III-V or II-VI materials as gallium arsenide (GaAs), gallium indium phosphide (GaInP), copper indium diselenide (CIS), copper indium- allium diselenide (CIGS), and cadmium telluride (CdTe).

In 1987, Jerry Olson reported a two-junction tandem photovoltaic device consisting of an upper GaInP layer and lower GaAs layer, with a photoconversion efficiency up to 29.5% under concentrated solar light. The addition of a third junction further increases the conversion efficiency, to 34% for a GaInP/GaAs/Ge solar cell, to 40% for a GaInP/GaAs/GaInAs cell. It is believed that the photoconversion efficiency of multi- (or many) junction solar cells can be increased up to 55%.

For example, highly mis-matched alloys such as Zn(1-y)Mn(y)O(x)Te(1.x) have shown utility in the high performance high dollar solar cell markets, such as in space satellites, where dollars are no issue but high photoconversion efficiency is. Unfortunately issues of cost limit application of solar cell technology in the ‘real’ world. The solar cell market continues to be dominated by silicon, the fabrication of which is energy-intensive requiring a manufacturing energy input equal to several years of energy output of the solar device.

Furthermore modest device efficiencies correspond to large land area requirements to meet the intrinsic energy demands of modern society. Generally speaking, as of today the cost of energy from solar cells is ˜ five times that produced by the burning of fossil fuels. However since fossil fuels are freely provided by nature, and still so cheap as to be commonly treated as free (and not treated as an irreplaceable precious commodity), the factor of five looks pretty modest.