37 research outputs found
Transparent yttrium hydride thin films prepared by reactive sputtering
Metal hydrides have earlier been suggested for utilization in solar cells.
With this as a motivation we have prepared thin films of yttrium hydride by
reactive magnetron sputter deposition. The resulting films are metallic for low
partial pressure of hydrogen during the deposition, and black or
yellow-transparent for higher partial pressure of hydrogen. Both metallic and
semiconducting transparent YHx films have been prepared directly in-situ
without the need of capping layers and post-deposition hydrogenation. Optically
the films are similar to what is found for YHx films prepared by other
techniques, but the crystal structure of the transparent films differ from the
well-known YH3 phase, as they have an fcc lattice instead of hcp
Surface oxide on thin films of yttrium hydride studied by neutron reflectometry
The applicability of standard methods for compositional analysis is limited
for H-containing films. Neutron reflectometry is a powerful, non-destructive
method that is especially suitable for these systems due to the large negative
scattering length of H. In this work we demonstrate how neutron reflectometry
can be used to investigate thin films of yttrium hydride. Neutron reflectometry
gives a strong contrast between the film and the surface oxide layer, enabling
us to estimate the oxide thickness and oxygen penetration depths. A surface
oxide layer of 5-10 nm thickness was found for unprotected yttrium hydride
films
A new thin film photochromic material: Oxygen-containing yttrium hydride
In this work we report on photochromism in transparent thin film samples of
oxygen-containing yttrium hydride. Exposure to visible and ultraviolet (UV)
light at moderate intensity triggers a decrease in the optical transmission of
visible and infrared (IR) light. The photo-darkening is colour-neutral. We show
that the optical transmission of samples of 500 nm thickness can be reduced by
up to 50% after one hour of illumination with light of moderate intensity. The
reaction is reversible and samples that are left in the dark return to the
initial transparent state. The relaxation time in the dark depends on the
temperature of the sample and the duration of the light exposure. The
photochromic reaction takes place under ambient conditions in the as-deposited
state of the thin-film samples.Comment: Accepted for publication in Solar Energy Materials and Solar Cell
Absorption Coefficient of a Semiconductor Thin Film from Photoluminescence
The photoluminescence (PL) of semiconductors can be used to determine their absorption coefficient (a) using Planck's generalized law. The standard method, suitable only for self-supported thick samples, like wafers, is extended to multilayer thin films by means of the transfer-matrix method to include the effect of the substrate and optional front layers. a values measured on various thin-film solar-cell absorbers by both PL and photothermal deflection spectroscopy (PDS) show good agreement. PL measurements are extremely sensitive to the semiconductor absorption and allow us to advantageously circumvent parasitic absorption from the substrate; thus, a can be accurately determined down to very low values, allowing us to investigate deep band tails with a higher dynamic range than in any other method, including spectrophotometry and PDS