Low cost and efficient photovoltaic conversion by nanocrystalline solar cells

Abstract

The quality of human life depends to a large degree on the availability of energy sources. The present worldwide energy consumption already exceeds the level of 6000 gigawatt and is expected to further increase sharply. This implies enhanced depletion of fossil fuel reserves, leading to further aggravation of the environmental pollution. Adding to this the dangers arising from the accumulation of plutonium fission products from nuclear reactors, the quality of life on earth is threatened unless renewable energy resources can be quickly developed. Photovoltaic solar energy converters are expected to make important contributions to the identification of environmentally friendly solutions to the energy problem. One attractive strategy discussed in this paper is the development of systems that mimic natural photosynthesis in the conversion of solar energy for the fixation of carbon dioxide. We have developed a molecular photovoltaic device whose overall efficiency for solar energy conversion to electricity has already attained 10%. The system is based on the sensitization of nanocrystalline films by transition metal charge transfer sensitizers. In analogy to photosynthesis, the new chemical solar cell achieves the separation of the light absorption and charge carrier transport processes. Extraordinary yields exceeding 90% for the conversion of incident photons into electric current are obtained, in contrast to conventional photovoltaic cells which are not economical for base load utility electricity production. The low cost and ease of production of the new cell should benefit large-scale applications, in particular in underdeveloped or developing countries, which benefit from generous sunshine. Aside from its intrinsic merits as a photovoltaic device, nanocrystalline film development opens up a large number of additional avenues for energy storage ranging from intercalation batteries to the formation of chemical fuels. These systems will undoubtedly promote the acceptance of renewable energy technologies, not least by setting new standards of convenience and economy.