Showing papers by "Andrew Hamnett published in 1981"

Photoelectrochemistry of nickel(II) oxide

Abstract: The electrochemistry and photoelectrochemistry of a (110) face of single-crystal lithiated NiO has been studied. The Mott–Schottky and photocurrent appearance potential suggest a flat-band potential of +0.8 V (NHE), and earlier capacitance data are used to fix a second acceptor level at +0.4 eV above the Li acceptor states. A simple geometrical interpretation of the anodic transients at 0.95 and 1.30 V (NHE) is provided, and the Tafel slope observed at anodic potentials is shown to be consistent with an electrochemical process having charge transfer as a rate-determining step. The optical data are interpreted with an energy-level scheme using a value of ca. 3 eV for the Hubbard parameter U defining the correlation splitting of the Ni 3d8 and Ni 3d9 configurations, and the data are consistent with a direct allowed transition at the band edge that is assigned to O 2p6→ Ni 3d9. Comparison with the X.p.e.s. spectrum and the known position of the O 2p6 band edge in other transition-metal oxides leads to a suggested Ni 3d8–O 2p6 band-edge separation of ca. 1.4 eV. The very low efficiencies found for NiO can be understood only if the minority-carrier diffusion length becomes comparable with the semiconductor Debye length. The very low ratio of free carriers to trapped holes in NiO is shown to make this material impractical for solar-energy devices.

The Transport and Kinetics of Minority Carriers in Illuminated Semiconductor Electrodes

Abstract: The differential equation describing the transport and kinetics of photogenerated minority carriers in a semiconductor electrode is solved analytically to obtain a solution in terms of confluent hypergeometric functions. Much simpler approximate solutions are also obtained. Comparison of these solutions with results from the full expression show that the approximate solutions hold to within 5%. A simple physical significance can be attached to the different terms in the approximate solutions. The form of the photocurrent voltage curves that arise from the different solutions is discussed.