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Photoelectrochemical cells
Michael Grtzel
Institute of Photonics and Interfaces, Swiss Federal Institute of Technology, CH-1015, Lausanne, Switzerland (e-mail [email protected])
Until now, photovoltaics the conversion of sunlight to electrical power has been dominated by solid-state junction devices, often made of silicon. But this dominance is now being challenged by the emergence of a new generation of photovoltaic cells, based, for example, on nanocrystalline materials and conducting polymer films. These offer the prospect of cheap fabrication together with other attractive features, such as flexibility. The phenomenal recent progress in fabricating and characterizing nanocrystalline materials has opened up whole new vistas of opportunity. Contrary to expectation, some of the new devices have strikingly high conversion efficiencies, which compete with those of conventional devices. Here I look into the historical background, and present status and development prospects for this new generation of photoelectrochemical cells.
Semiconductor electrode
Ever since the French scientist Edmond Becquerel1 discovered the photoelectric effect, researchers and engineers have been infatuated with the idea of converting light into electric power or chemical fuels. Their common dream is to capture the energy that is freely available from sunlight and turn it into the valuable and strategically important asset that is electric power, or use it to generate fuels such as hydrogen. Photovoltaics takes advantage of the fact that photons falling on a semiconductor can create
electronhole pairs, and at a junction between two different materials, this effect can set up an electric potential difference across the interface. So far, the science of solar cells has been dominated by devices in which the junction is between inorganic solid-state materials, usually doped forms of crystalline or amorphous silicon, and profiting from the experience and material availability resulting from the semiconductor industry. Recently, we have seen more use of devices made from compound semiconductors the III/V compounds for high-efficiency aerospace components and the copperindiumsulphide/selenide materials for thin-film, low-cost terrestrial cells. But the dominance of the field by inorganic solid-state junction devices faces new challenges in the coming years. Increasingly, there is an awareness of the possible advantages of nanocrystalline and conducting polymer devices, for example, which are relatively cheap to fabricate (the expensive and energy-intensive high-temperature and high-vacuum processes needed for the traditional devices can be avoided),...