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Electric Power Generation from Sunlight by Mesoscopic Solar Cells

Michael Graetzel 

Ecole Polytechnique Federale de Lausanne (EPFL), Ecublens, Lausanne 1015, Switzerland


The recently discovered photovoltaic cells based on mesoscopic semiconductors are commonly referred to as “bulk“ or interpenetrating network junctions due to their three- dimensional structure. These are formed for example from inorganic oxides, ionic liquids and organic hole conductors or conducting polymers, offering the prospect of low cost fabrication without expensive and energy intensive high temperature and high vacuum steps, compatibility with flexible substrates and a variety of presentations and appearances to facilitate market entry. Contrary to expectation, these new solar cells have shown strikingly high conversion efficiencies, competing with conventional systems. Mesoscopic injection solar cells operate in an entirely different fashion than conventional solar p-n junction devices. Mimicking the principles that natural photosynthesis has used successfully over the last 1.5 billion years in solar energy conversion, they achieve the separation of light harvesting and charge carrier transport. The semiconductors used in conventional cells assume both functions simultaneously imposing stringent demands on purity and entailing high material and production costs. The prototype of this family of devices is the dye-sensitzed solar cell (DSC), which accomplishes the optical absorption and the charge separation processes by the association of a sensitizer or quantum dot as light-absorbing material with a wide band-gap oxide semiconductor of nanocrystalline morphology. Conversion efficiencies exceeding 11 % and impressive stability results have fostered first industrial applications. It appears that this type of cell is a viable contender for large-scale future solar energy conversion systems on the bases of cost, efficiency, stability and availability as well as environmental compatibility.


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Presentation: Invited at E-MRS Fall Meeting 2007, Symposium A, by Michael Graetzel
See On-line Journal of E-MRS Fall Meeting 2007

Submitted: 2007-05-09 19:32
Revised:   2009-06-07 00:44