Showing papers by "Nathan S. Lewis published in 1987"

Chemical modification of n-GaAs electrodes with Os3+ gives a 15% efficient solar cell

Abstract: The minimization of interfacial recombination losses is a key factor in the operation of any semiconductor-based solar-energy-conversion device, including solid-state junctions, semiconductor/liquid junctions and colloidal suspensions of semiconductors. A frequently cited advantage of semiconductor/liquid junctions is the ability to manipulate surface recombination rates by chemical reactions1–7. A notable example is the improvement in current–voltage properties of n-GaAs photoanodes which have been exposed to aqueous solutions of Ru3+ ions8–10. Here we report new surface-modification procedures for GaAs which have produced the most efficient photoelectrochemical cell reported to date. We also report experiments which indicate that the current–voltage improvements in this system are accompanied by increased interfacial hole transfer rates at the GaAs/liquid interface.

Opportunities in semiconductor photoelectrochemistry

Abstract: Les problemes rencontres en photoelectrochimie des semiconducteurs sont rapportes: developpement de cellules solaires a jonction n-Si/liquide; croissance photoelectrochimique des cellules de type MIS; etude de la chimie interfaciale des materiaux III-V; processus chimiques pour minimiser les pertes de recombinaison aux joints de grain et aux etats de surface des interfaces de Si et de GaAs

Coordination chemistry of semiconductor photoelectrodes: reactions of etched n-GaAs with Co(III) complexes

Abstract: The authors report studies of the reactivity of n-GaAs surfaces with transition-metal complexes. Generally, adsorption of metal ions at semiconductor junctions has been observed to increase carrier trapping rates. A notable exception is the improved performance of n-GaAs interfaces after exposure to acidic aqueous solutions of Ru(III) ions and other metal cations, but little information is available regarding the chemistry of these surface treatments. Except for systems in which metal ions act as precursors for the deposition of metals or metal alloys, no information is available regarding the oxidation state or chemical environment of chemisorbed transition-metal complexes on semiconductor electrodes. Possible but undocumented mechanisms of metal ion attachment to the semiconductor surface include electrostatic binding, ligand substitution processes, and redox reactions. To explore the various possible modes of reaction, they have investigated the chemistry of n-GaAs surfaces in contact with aqueous solutions of Co(III) complexes.

Coordination Chemistry of Semiconductor Photoelectrodes: Reactions of Etched n‐GaAs with Co(III) Complexes.

Abstract: The authors report studies of the reactivity of n-GaAs surfaces with transition-metal complexes. Generally, adsorption of metal ions at semiconductor junctions has been observed to increase carrier trapping rates. A notable exception is the improved performance of n-GaAs interfaces after exposure to acidic aqueous solutions of Ru(III) ions and other metal cations, but little information is available regarding the chemistry of these surface treatments. Except for systems in which metal ions act as precursors for the deposition of metals or metal alloys, no information is available regarding the oxidation state or chemical environment of chemisorbed transition-metal complexes on semiconductor electrodes. Possible but undocumented mechanisms of metal ion attachment to the semiconductor surface include electrostatic binding, ligand substitution processes, and redox reactions. To explore the various possible modes of reaction, they have investigated the chemistry of n-GaAs surfaces in contact with aqueous solutions of Co(III) complexes.

Kinetic Studies of Ligand Substitution Rates for the Ru(NH3)5(H2O)2+ Ion in Nafion Films.

Abstract: Substitution rates have been measured for reaction of a number of pyridines with the Nafion-bound Ru(NH/sub 3/)/sub 5/(H/sub 2/O)/sup 2 +/ complex. Reaction activities have been determined by electrochemical techniques, which also allow for determination of site thermodynamics and heterogeneity during the course of the reaction. Diffusion-coefficient effects are investigated by variation in polymer film thickness, and partition coefficients have been determined under equilibrium conditions by optical absorbance techniques. The partition-coefficient corrected rate law is found to be first order in Nafion-bound (Ru/sup II/) and first order in ligand concentration in the polymer phase. The partition-coefficient corrected bimolecular rate constants for a variety of pyridine ligands are found to vary by a factor of 5, which contrasts with the relatively constant substitution rates observed in aqueous solution. Also, sterically hindered ligands, such as 2-propylpyridine, exhibit surprisingly high substitution rate constants on the Nafion-bound Ru/sup II/ ion. These rate data indicate that pronounced molecular reactivity changes can occur upon electrode modification and have implications with respect to the design of chemically modified electrodes for use in electrocatalysis.