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The field of photovoltaic cells has been dominated so far by solid state p-n junction devices made e.g. of crystalline or amorphous silicon, profiting from the experience and material availability of the semiconductor industry. However, there is an increasing awareness of the possible advantages of devices referred to as "bulk" junctions due to their interconnected three-dimensional structure. Their embodiment departs completely from the conventional flat p-n junction solid-state cells, replacing them by interpenetrating networks.
This lecture focuses on dye sensitized mesoscopic solar cells (DSCs), which have been developed in our laboratory. Imitating the light reaction of natural photo-synthesis, this cell is the only photovoltaic device that accomplishes the separation of the optical absorption from the charge separation and carrier transport processes. It does so by associating a molecular dye with a film constituted of tiny particles of the white pigment titanium dioxide. The DSC has made phenomenal progress, present conversion efficiencies being over 12 percent for single junction and 17 percent for tandem cells, rendering the DSC a credible alternative to conventional p-n junction devices. Commercial large-scale production of flexible DSC modules has started in 2009. These solar cells have become viable contenders for large-scale future solar energy conversion systems on the bases of cost, efficiency, stability and availability as well as environmental compatibility.
Prof. Dr. Michael Grätzel (Ecole Polytechnique Fédérale de Lausanne, Laboratory of Photonics and Interfaces)