The light-induced electron-hole generation, separation and migration are important processes for the conversion of light to electric or chemical energy (solar cells; photosynthesis), the latter being the basis of life on earth. Most of the world's current energy supplies are based on fossil energy sources and only a little is provided by hydropower, biomass and nuclear energy. The exponential growth of CO_2 level in the atmosphere is leading to the threat of a worldwide climate change. Also, there will be limited availability of fossil energy sources in the long term. Exploitation of nuclear energy does not appear to be socially acceptable, universally. The problem of energy provision, particularly in the Third World, remains unsolved. The alternative energy sources are the renewable energy sources. The overflowing solar energy is the most promising source for future sustainable production of fuel and electricity. The photovoltaic effect, the direct conversion of light energy into electricity by solar cells, is known since 1839 but until the mid-twentieth century it remained mostly a laboratory curiosity. The space programme (scientific, commercial and military satellites) gave tremendous impetus to the development of solar cells. The oil crisis of 1973 forced many countries to look for alternative sources of energy and interest in photovoltaics as a terrestrial source of power increased greatly.
展开▼
