Solar energy, conversion electricity

Much use has been made of micellar systems in the study of photophysical processes, such as in excited-state quenching by energy transfer or electron transfer (see Refs. 214-218 for examples). In the latter case, ions are involved, and their selective exclusion from the Stem and electrical double layer of charged micelles (see Ref. 219) can have dramatic effects, and ones of potential imfKntance in solar energy conversion systems. 

Despite the potential impact of novel photosynthetic routes based on these developments, the most ambitious application remains in the conversion of solar energy into electricity. Dvorak et al. showed that photocurrent as well as photopotential response can be developed across liquid-liquid junctions during photoinduced ET reactions [157,158]. The first analysis of the output power of a porphyrin-sensitized water-DCE interface has been recently reported [87]. Characteristic photocurrent-photovoltage curves for this junction connected in series to an external load are displayed in Fig. 22. It should be mentioned that negligible photoresponses are observed when only the platinum counterelectrodes are illuminated. Considering irradiation AM 1, solar energy conversions from 0.01 to 0.1% have been estimated, with fill factors around 0.4. The low conversion... 

For the longer term, there is the solar energy conversion challenge. Once solar radiation is efficiently captured it will be stored in the form of hydrogen or electricity, with major challenges again for electrocatalysis. 

However, there are many challenges to exploiting direct conversion of solar energy into electricity and/or chemical fuels. For a comprehensive review of the basic research challenges in the photovoltaic conversion of solar energy see Refs. [2, 3, 9]. 

The first issue can be addressed in two ways a primary ET species which has a large optical absorption cross-section can be chosen or arrays of molecules with large optical absorption cross-sections can be used as "antennas" that will efficiently collect and transport the electronic excitation energy to the primary ET species, in direct analogy to photosynthetic systems. While in the latter case it should be possible to develop systems with more efficient solar photon collection, the number of primary ET species will have to be reduced due to the spatial limitations, which will also reduce the potential electric current that can be produced by the system. Thus, questions related to the detailed molecular architecture of biomimetic solar energy conversion devices will have to address this issue, and it is quite likely that a number of compromises will have to be made before optimal design characteristics are obtained. 

For reviews of photovoltaic principles and applications, consult Merrigan, J.A., "Sunlight to Electricity - Prospects for Solar Energy Conversion by Photovoltaics", MIT Press, Cambridge, Mass., 1975 "Solar Cells", C.E. Backus, ed.,... 

The most direct solar energy conversion for the production of electricity [15] is... 

Solar energy-to-electricity conversion efficiency (rf) under white-light irradiation (e.g., AM 1.5) can be obtained from... 

Recently, the DSSC has been used for an educational demonstration of solar energy-to-electricity conversion system because of its simple fabrication [12,168]. Students could purchase DSSC kits including all components such as TCO-coated glass, 2 electrodes, blackberries (i.e., dye), and electrolyte solution [169,170] and easily demonstrate an artificial photosynthetic process. For detailed studies, it is possible to purchase raw materials, including Ru dye photosensitizers, Ti02 paste, and sealing materials, from Solaronix S. A. [171]. 

In photo-catalytic and solar energy conversion devices, the absorption of a photon results in the generation of electrons and holes, which, upon separation, can provide an electric potential or trigger chemistry. The efficiency of these devices is frequently determined by the transport of the charges following photo-generation. In particular, for TiC>2-based dye-sensitized solar cells, it has been demonstrated that the efficiency is limited by electron transport through TiC>2 nanoparticles [1]. 

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