Programm Photovoltaik Ausgabe 2008 ... - Bundesamt für Energie BFE

Eidgenössisches Departement für
Umwelt, Verkehr, Energie und Kommunikation UVEK
Bundesamt für Energie BFE
DYE-SENSITISED NANOCRYSTALLINE
SOLAR CELLS
Annual Report 2007
Author and Co-Authors Michael Grätzel; Augustin McEvoy
Institution / Company Laboratory for Photonics and Interfaces (LPI),
Faculty of Basic Sciences
Address Station 6, Ecole Polytechnique Fédérale de Lausanne,
CH-1015 Lausanne
Telephone, E-mail, Homepage +41 21 693 31 12, michael.graetzel@epfl.ch;
http://isic.epfl.ch/graetzel_e.htm
Project- / Contract Number Project EPFL
Duration of the Project (from – to) January 2007 – December 2007
Date December 2007
ABSTRACT
Recently the historic trend to lower prices for photovoltaic cells, modules and systems has been reversed.
This is a particular challenge to the photovoltaic industry, at a time when general energy
prices are also rising and a breakthrough opportunity is presented. The price rise centres on the
availability of photovoltaic-quality silicon for the conventional solid state devices. In these circumstances
the interest in thin-film devices, including sensitised photoelectrochemical and heterojunction
devices, becomes even more intense. Sensitised photoelectrochemical devices are a significant
technical and commercial alternative to those conventional solid-state junction photovoltaic devices
for solar energy applications. In the standard solid state photovoltaic devices semiconductor layers
absorb light and thereby produce electron-hole pairs, which are subsequently separated to provide a
photovoltage by junctions, either with other semiconductors or at Schottky contacts with metals. In the
photoelectrochemical system the contacting phase is an electrolyte. However standard semiconductors
with absorption properties compatible with visible light are in general unstable in contact with
electrolytes. Wide bandgap semiconductors are suitable, if sensitised to the visible spectrum by electroactive
dyes. In the dye-sensitised system the recombination loss mechanism is minimised since
the processes of optical absorption and charge separation take place on distinct phases within these
photovoltaic cells. In consequence oppositely charged species are restricted to separate phases.
Therefore device photoconversion efficiency is maintained even at low light levels. Recent results on
enhanced device stability are particularly significant for future commercial applications.
Sensitised heterojuctions, which are a further option in the development of low-cost thin film photovoltaic
deviices, are also under development in this laboratory.
A hybrid variant is also under investigation, the dye-sensitised solid state heterojunction, where the
electrolyte phase is replaced by an organic charge transport medium. A further implementation of the
dye-sensitised cell is as a component in optical-series tandem cells, for extended spectral matching
or for photoelectrolysis.
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