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Content archived on 2024-04-19

Efficient transparent photovoltaic cells based on polycrystalline TI02 thin films sensitized by molecular antennae


The objective of the project is to pursue programmes of basic and applied research leading to optimization and commercialization of efficient transparent photovoltaic cells based on TiO2.
Optimization of this type of PV cell will involve detailed study of all discrete intermediate steps between photon absorption and generation of the photocurrent in order to identify and minimize losses associated with each step.
Commercialization of the cell will be facilitated by development of an all solid state device and improved long-term stability.

A transparent regenerative photoelectrochemical cell was successfully developed. It uses low to medium purity materials and simple construction processes, so it will be easy to make on an industrial level in the future. The cell is up to five times cheaper than traditional cells. It has achieved an average conversion efficiency of 10%, although up to 12 % is possible, depending on the conditions. The cell produces a large current and has been shown to have a long simulated life time; over 20 years. The electricity it produces is relatively low in cost at about 500 ECU per kW.
Graetzel and co-workers have described a transparent regenerative photoelectrochemical cell, utilizing low to medium purity materials and simple construction processes, with a light to electric energy conversion efficiency of between 7 % and 12 %. A monomeric ruthenium complex has been developed having an improved response to red light and yielding an overall efficiency of 10.4%. The large current efficiency, exceptional stability (sustaining at least 5 million turnovers without decomposition) and low cost, make practical applications of this cell feasible.
The cell is based on an optically transparent TiO2 film, consisting of fused 10 nm anatase particles, which has a surface roughness factor of about 500. This film is coated by a monolayer of antenna molecules, i.e. by a monolayer of a charge transfer dye whose absorption spectrum overlaps well with the solar emission spectrum. An incident solar photon is reflected many times in this film, passing repeatedly through the monomolecular dye layer, and is absorbed. The cell harvests a high proportion of the incident solar energy flux (46%) and shows exceptionally high efficiencies for conversion of incident photons to electric current (greater than 80%). The exciton created by the absorbed photon travels only a very short distance in the monomolecular dye layer to reach the site at the interface where electron-hole pair separation occurs. The electron moves away from the interface along a potential gradient through a succession of fused TiO2 particles to the conducting glass substrate and then passes through the external circuit to the counter electrode. The oxidized dye molecule is regenerated by a sacrificial donor which is in turn reduced by electrons available at the counter electrode.

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Stillorgan Road Belfield
4 Dublin

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