Publication costs assisted try Colorado State UniversityPhotosynthetic production of H2 and H202 is demonstrated on UV-irradiated ZnO/water and Ti02/water suspensions. The rates of H2 and H202 production were monitored by a combined analytical-gas chromatographic procedure as a function of irradiation time and solid content. In the case of ZnO, evidence is presented which indicates that photocorrosion of ZnO proceeds simultaneously with photosynthesis of H2 and HzOD The present data are rationalized with the aid of energy band diagrams showing the relative positions of the semiconductor band edges and the solution redox levels. IntroductioinThere has lbeen much recent interest in photocatalytic and photosynthetic processes at the a,emiconductor/liquid interface-l Interest in photosynthetic processes stems primarily from the possibility of utillizing these reactions to convert sunlight to storable forms of energy. Two reactions which have received particular attention in this regard are Both of these reactions are thermodynamically "uphill" and involve respectively free-energy changes of 2.43 and 1.26 eV per molecule. Photoelectrochemical (PEC) methods h a w offered a ready means of overcoming the thermodynamic barriers and have einabled production of fuels by reactions 1 and 2. Several rleviews of this field of research have appeared in the recent literaturea2 An attractive alternative to the PEC approach involves the socalled photoriynthetic m0de.l' This approach utilizes semiconducting grains which are suspended in the appropriate reaction media and thereby affords a more practical means of carrying out the energy conversion process. Each illuminated grain may be regarded as a short-circuited PEC cell, and the reactions at the interface of each grain and the liquid medium constitute the "local cell"ld,fJ processes.Photosynthetic production of Hz02 according to reaction 2 has been investigated on various semiconducting materials including ZnO?s5 CdS,4 HgS: ZnS,4 CdTe,6 CdSe,4 and Ga2S3.4 ZnO, in particular, has been the focus of considerable a t t e n t i~n .~,~ Notwithstanding the controversies that remain on the mechanism of photosynthesis of Hz02 at the ZnO/liquid i~i t e r f a e e ,~~ it was particularly of interest to note that previous authors had reported no traces of hydrogen in the reaction products.3c In view of the importance of reaction 1 to energy conversion and storage and the preponderance of this reaction at oxide semiconductor/electrolyte interfaces in general (vide infra), we decided to reexamine the products of UV-generated processes at the powdered ZnO/liquid interface.A second aspect of relevance to this paper concerns reaction 2. Pirevious authors had observed H202 production at the Ti02/electrolyte interface subjected to UV and visible irradiation.6 These experiments were, however, conducted in the photoelectrochemical mode. With powdered Ti02 grains suspended in aqueous solution, no evidence for reaction 2 was obtained in previous studies.3a This finding was surprising particularly in vie...

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Recently 12% efficient indium tin oxide (ITO) on silicon solar cells have been reported. Experiments indicate the presence of a thin interfacial insulating layer. Thus, these devices appear to belong to a class of semiconductor-insulator-semiconductor (SIS) solar cells where one of the semiconductors is a degenerate wide-band-gap oxide. We have developed a theory in terms of minority-carrier tunnel current transport through the interfacial layer where one semiconductor is in a nonequilibrium mode. The wide-band-gap semiconductor serves to block band-to-band majority-carrier current and thus, in principle, give better device performance than with an MIS solar cell. The effects of interfacial layer thickness, substrate doping level, surface states and interface charge, temperature on the performance of SIS solar cells have been calculated. These indicate that real-world ITO on silicon cells should be able to achieve 20% efficiency under AMl illumination. Other combinations of semiconductors would yield even better performance.

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We have reported on the theory of semiconductor-insulator-semiconductor (SIS) solar cells in a previous publication. In this paper, the fabrication and properties of indium tin oxide/p-Si single-crystal solar cells will be described. The ITO is deposited by the ion-beam sputtering method. Best photovoltaic devices are obtained when the composition of indium tin oxide (ITO) is 91 mole% and 9 mole% SnO2. The device properties as a function of the ITO composition will be described. The thickness and the composition of the oxide-silicon interface is critical for device performance. The existence of a thin interfacial layer is demonstrated by Auger spectroscopy. The effect of temperature on device performance and the spectral response are compared with the theory. The SIS model accurately matches the major trends observed in experimental nITO/p-Si solar cells.

Arrangement of band structure for organic-inorganic photovoltaics embedded with silicon nanowire arrays grown on indium tin oxide glass Appl. Phys. Lett. 95, 053302 (2009);

Relaxation phenomena in thin polyaniline films synthesized chemically and electrochemically are investigated by UV-vis and IR spectroscopy. It is shown that the relaxation process carried out from the electrochemically oxidized or electrochemically reduced states of the polyaniline always proceeds toward the emeraldine state. The relaxation process in acid is governed by disproportionation and formation of semiquinone radicals. The changes in the population density of the polaronic states within the polaronic band allows determination of the change in the oxidation state and consequently the change in the position of the Fermi energy level. The formation of polaronic states is ascertained by diffusion of ions from or into the polyaniline matrix in solution and within the polymer in air.* To whom correspondence should be addressed.f Pacific Northwest Laboratory is a multiprogram national laboratory operated by Battelle Memorial Institute for the U.S. Department of Energy under Contract DE-AC06-76RLO #1830.