Abstract (EN):
In this work Nb-doped TiO2 thin films were deposited by d.c.-pulsed reactive magnetron sputtering at 500 °C
from a composite target with weight fractions of 96% Ti and 4% Nb, using oxygen as reactive gas. In order to
enhance the conductive properties, the as-deposited samples were treated in vacuum with atomic hydrogen
at a substrate temperature of 500 °C. The atomic hydrogen flow was generated by a hot filament, inside a
high-vacuum chemical vapour deposition reactor, at a temperature of 1750 °C. In order to optimise the hydrogen
hot-wire treatments, the H2 pressure was varied between 1.3 and 67 Pa, the treatment time was monitored
between 1 and 5 min and the hot-filament current was changed between 12 and 17 A. Dark
conductivity was measured as a function of temperature and its value at room temperature was extrapolated
and used to assess the effect of the hydrogen annealing on the charge transport properties. A two-order of
magnitude increase in dark conductivity was typically observed for optimised hydrogen treatments
(10 Pa), when varying the hydrogen pressure, resulting in a minimum resistivity of ~3× 10¿3 ¿ cm at
room temperature. The maximum amount of atomic H incorporation in oxygen vacancies was determined
to be ~5.7 at.%. Carrier mobility and resistivity were also investigated using Hall effect measurements. Correlations
between structural and electrical properties and the hydrogen treatment conditions are discussed.
The purpose of these films is to provide a transparent and conductive front contact layer for a-Si based photovoltaics,
with a refractive index that better matches that of single and tandem solar cell structures. This can
be achieved by an appropriate incorporation of a very small amount of cationic doping (Nb5+) into the titanium
dioxide lattice.
Idioma:
Inglês
Tipo (Avaliação Docente):
Científica
Notas:
Publicação abrangida pelo Journal Citation Reports 2015
Nº de páginas:
6