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Kim et al. Soft Sci 2024;4:33 https://dx.doi.org/10.20517/ss.2024.28 Page 25 of 31

Table 6. Summary of the characteristics of published data on CuI for TEGs

Electrical Seebeck Power Thermal
Materials conductivity coefficient factor conductivity Measurement zT Year Ref.
temperature (K)
-1
-1
-1
-2
-1
-1
(S·cm ) (μV·K ) (μW·m ·K ) (W·m ·K )
[27]
I doped CuI - 172 375 0.55 300 0.21 2017
CuI (300 nm thick) 110 206 - 0.48 - 0.29 2019 [142]
[145]
CuI with 0.05 M NaI - 115 66.1 - RT - 2019
precursor
[146]
100 °C annealed CuI 11.8 789. 740.9 - RT - 2020
(Ar atmosphere)
[146]
Vacuum annealing - 561.8 443.5 - RT - 2021
S implanted CuI 25.9 498.6 642.9 - RT - 2022 [147]
[150]
I doping CuI 5.43 308 - - RT - 2022
[47]
CuI 84.22 232.1 454 - RT - 2023
Two-step annealed 152 711 66 - 412 - 2023 [56]
CuI
I doped CuI 207.6 180.1 673.3 0.66 RT 0.31 2023 [148]
CuI: Copper iodide; TEGs: thermoelectric generators; RT: room temperature.
In 2023 and 2024, numerous researchers studied CuI thin films for TEG applications from various
perspectives. Darnige et al. fabricated CuI thin films using a solid iodination method and annealed the films
under specific conditions. They found that the optimal annealing conditions for stable electrical
conductivity were 300 °C annealing in an Ar atmosphere flowed by 150 °C annealing in the air. This
annealing process induced structural rearrangement, reducing Cu defects, and the air annealing introduced
-1
O doping, slightly increasing electrical conductivity. The electrical conductivity stabilized at 152 S·cm . The
Seebeck coefficient was measured across different temperatures, ranging from 287 μV·K at 44 °C to
-1
-1
711 μV·K at 139 °C . Bae et al. reported on iodine-doping CuI thin films and developed transparent and
[56]
flexible thermoelectric devices. The CuI thin film was fabricated by spray coating with additional iodine in
-1
the precursor to achieve stoichiometric balance. They achieved an electrical conductivity of 207 S·cm and a
-1
-2
-1
Seebeck coefficient of 180.1 μV·K . The optimized power factor was 673.3 μW·m ·K , and the zT was
0.31 . Thimont et al. investigated CuI-based thermoelectric devices. The CuI film was made via an
[148]
iodination process, and they optimized the module length and number through modeling based on
experimental results of electrical conductivity and the Seebeck coefficient across various temperatures. The
-1
electrical conductivity and Seebeck coefficient ranged from around 35 to 55 S·cm and 400 to 800 μV·K ,
-1
respectively. The thermoelectric device modules were optimized with a length of 13 mm and three tracks.
[149]
While increasing the length or number of tracks increased the V , it also raised internal resistance .
OC
Table 6 indicates the summarized properties of CuI TEGs.
CONCLUSION AND OUTLOOK
In this paper, we investigated recent progress of CuI for electronics, optoelectronics, and energy
applications, as a transparent p-type semiconductor. While metal oxides have been commercialized as
transparent semiconductors with excellent electrical and optical properties as n-type materials, there has
been a lack of suitable p-type semiconductors for several decades. CuI exhibits high electrical performance,
transmittance, and flexibility, and can be fabricated using various methods. In addition to its excellent
optoelectronic performance, its abundance on earth, low cost, and non-toxicity make CuI promising for
industrial implementation. We examined the underlying physics that gives CuI its excellent electrical