Highly transparent p-type γ-CuI thin films with
enhanced
thermoelectric (TE) properties were produced by the pulsed laser deposition
(PLD) technique. The film composed of fine nanoparticles was found
to show transparency close to 90% and excellent TE performance at
300–360 K. Postannealing at three different temperatures in
the range of 373–573 K in a vacuum was found to diminish the
deviation from the stoichiometric composition, namely, δ in
Cu1−δI, possibly due to iodine evaporation.
The carrier (hole) concentration decreased and the Hall mobility increased
on increasing the postannealing temperature, i.e., by decreasing δ.
The film postannealed at 373 K showed the best TE performance with
a high electrical conductivity of ∼14 000 S/m, a large
Seebeck coefficient of ∼350 μV/K, and a high power factor
of ∼1600 μW/(m K2) at 300 K. The degeneracy
of the heavy- and light-hole bands of γ-CuI could enhance the
Seebeck coefficient through enhancing the effective mass of holes
and decreasing the carrier concentration, while electrical conductivity
was only slightly decreased. Thermal conductivity of the γ-CuI
thin films was verified to be as low as 0.77–0.83 W/(m K) at
300 K. The present study firmly demonstrates the high potential of
the γ-CuI thin film as a p-type TE material to be paired with
an n-type material for flexible TE devices and self-powered electronic
systems operating at 300–360 K.
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