Photovoltaik, Stand der Technik und Perspektiven der nanokristallinen Injektionszelle

Zusammenfassung

Herkömmliche Solarzellen wandeln Licht in Elektrizität um, indem sie den an der Grenzfläche zweier Halbleiter auftretenden photoelektrischen Effekt ausnützen. Im Gegensatz dazu erfolgt in einer neuen Art von Solarzellen die Umwandlung von Licht in elektrische Energie mittels Redoxprozessen, ähnlich wie sie in der natürlichen Photosynthese ablaufen. Der vorliegende Artikel beschreibt den Mechanismus solcher Zellen und zeigt, daß auch diese Technologie für einen zukünftigen Großeinsatz der Photovoltaik zur Energieumwandlung in Frage kommen könnte.

Abstract

A new molecular photovoltaic system for solar light harvesting and conversion to electricity has been developed. It is based on the spectral sensitization of a nanocrystalline semiconductor film by transition metal complexes. The film consists of nanometersized colloxidal titanium dioxide particles sintered together to allow for charge carrier transport. Ruthenium- and osmium-based sensitizers have so far achieved the best performance, both from the efficiency as well as the stability point of view. Carboxylated and phosphonated polypyridyl complexes of these two metals give extraordinary efficiencies for the conversion of incident photons into electric current, exceeding 90 percent within the wavelength range of their absorption band. For several years, the outstanding performance of cis-di(thio-cyanato)bis(2,2′-bipyridyl-4,4′-dicarboxylate)ruthenium(II) was unmatched by any other sensitizer. Only very recently have phosphonated terpyridyl complexes of ruthenium been developed that achieve similar photovoltaic performance. The present paper discusses the underlying physical principles of these astonishing findings. Exploiting this discovery, we have developed a lowcost photovoltaic cell whose overall light to electric energy conversion yield is 10 percent under direkt (AM 1.5) solar irradiation. For the first time, a device based on a simple molecular light absorber is attaining a conversion efficiency commensurate with that of silicon-based photovoltaic cells, but at a much lower cost.