Surface Defect Passivation and Reaction of c-Si in H2S.

A unique passivation process of Si surface dangling bonds through reaction with hydrogen sulfide (H2S) is demonstrated in this paper. A high-level passivation quality with an effective minority carrier lifetime (τeff) of >2000 µs corresponding to a surface recombination velocity of <3 cm/s is achieved at a temperature range of 550-650 °C. X-ray photoelectron spectroscopy (XPS) confirmed the bonding states of Si and S and provides insights into the reaction pathway of Si with H2S and other impurity elements both during and after the reaction. Quantitative analysis of XPS spectra showed that the τeff increases with an increase in the surface S content up to ∼3.5% and stabilizes thereafter, indicative of surface passivation by monolayer coverage of S on the Si surface. However, S passivation of the Si surface is highly unstable because of thermodynamically favorable reaction with atmospheric H2O and O2. This instability can be eliminated by capping the S-passivated Si surface with a protective thin film such as low-temperature-deposited amorphous silicon nitride.

A new photoelectrochemical test cell and its use for a combined two-electrode and three-electrode approach to cell testing.

This paper describes the design, assembly, and operation of a photoelectrochemical (PEC) test cell that is relatively easy to construct and well suited for testing photoelectrode/counterelectrode combinations in a reproducible manner. The design of the cell permits measurements to be made in both two-electrode and three-electrode arrangements. The benefits of conducting both two-electrode and three-electrode measurements are illustrated using data obtained from the new test cell for a PEC system based on a polysulfide electrolyte, CdSe(0.8)Te(0.2) photoanode, and tungsten monocarbide counterelectrode. It is shown that linear sweep voltammograms measured in three-electrode mode can be used to describe current transients recorded in a two-electrode cell modified by the addition of a reference electrode.

Development of CuInSe2 nanocrystal and nanoring inks for low-cost solar cells.

The creation of a suitable inorganic colloidal nanocrystal ink for use in a scalable coating process is a key step in the development of low-cost solar cells. Here, we present a facile solution synthesis of chalcopyrite CuInSe 2 nanocrystals and demonstrate that inks based on these nanocrystals can be used to create simple solar cells, with our first cells exhibiting an efficiency of 3.2% under AM1.5 illumination. We also report the first solution synthesis of uniform hexagonal shaped single crystals CuInSe 2 nanorings by altering the synthesis parameter.