Power effect on the properties of copper nitride films as solar absorber
deposited in pure nitrogen atmosphere
Abstract
Nowadays, the copper nitride (Cu 3N) is of great
interest as a new solar absorber material, flexible and lightweight thin
film solar cells. This material is a metastable semiconductor,
non-toxic, composed of earth-abundant elements, and its band gap energy
can be easily tunable in the range 1.4 to 1.8 eV. For this reason, it
has been proposed for many applications in the solar energy conversion
field. The main aim of this work is to evaluate the properties of the Cu
3N thin films fabricated by reactive radio-frequency
(RF) magnetron sputtering at different RF power values to determine its
potential as light absorber. The Cu 3N films were
fabricated at room temperature (RT) from a Cu metallic target at the RF
power ranged from 25 to 200 W on different substrates (silicon and
glass). The pure nitrogen flux was set to 20 sccm, and the working
pressures were set to 3.5 Pa and 5 Pa. The XRD results showed a
transition from (100) to (111) preferred orientations when RF power
increased; the AFM images revealed a granular morphology, while FTIR and
Raman spectra exhibited the characteristics peaks related to Cu-N bonds,
which became narrower when the RF power increased. Finally, to stablish
the suitability of these films as absorber, the band gap energy was
calculated from transmission spectra.