Flexible thermoelectric power generation is a competitive candidate for powering wearable electronic devices and chip-sensor of internet-of-things. Nevertheless, the poor thermoelectric performance of n-type flexible thin film limits its application,...

With the increasing demand for wearable power supplies on the internet of things, [1][2][3][4] flexible thin-film thermoelectric devices (TEDs) with unique advantages of wearability and scalability have attracted everincreasing attention. [5][6][7] Typically, flexible thin-film TEDs are composed of highly flexible organic materials, such as polystyrene sulfonate acid (PEDOTS : PSS), [8] poly vinylidene fluoride, [9] polyaniline. [10] These devices exhibit high flexibility, where the key challenge lies in the low material performance. The overall material performance is evaluated by the dimensionless figure of merit, ZT = S 2 σT/κ = S 2 σT/(κ l + κ e ), and S, σ, T, κ, κ l , and κ e are the Seebeck coefficient, the electrical conductivity, the absolute temperature, the total thermal conductivity, the lattice thermal conductivity, and electrical thermal conductivities, respectively. [11][12][13] S 2 σ is generally defined as the power factor to estimate the overall electrical performance. [14] For typical p-type organic thermoelectric thin films, such as PEDOT:PSS, a room-temperature S 2 σ is generally <3 µW cm -1 K -2 with a corresponding ZT < 0.3. [15] For typical n-type organic thermoelectric thin films, such as PEDOT:PSS /CNTs, a room temperature ZT is generally <0.6. [16] To overcome the low performance of organic flexible thin-film TEDs, high-performance inorganic thermoelectric thin-films are increasingly studied. Specifically, both n-type and p-type Bi 2 Te 3based thin-films have been reported with room-temperature ZT of ≈1.22 and ≈1.5, respectively. [17,18] HgSe-based thin-films have also been reported with a room-temperature ZT of ≈0.68. [19] Rongione et al. [20] further reported the room-temperature ZT value as high as ≈1.17 of SnSe-based thin-films. Additionally, high room-temperature S 2 σ as high as 25 µW cm -1 K -2 have also been reported in carbon nanotubes. [21] With such high materials performance, these inorganic thin-film thermoelectric materials have been assembled into flexible TEDs. For example, Kim et al. [1,22] prepared a flexible inorganic thin-film TED, which is composed of 72 pairs of p-type Bi 0.5 Sb 1.5 Te 3 and n-type Bi 0.5 Te 2.7 Se 0.3 legs and realized a high voltage output (V out ) of 693 mV under a temperature difference of 25.6 K. Yang et al. [3] reported a high output power (P out ) of 137.5 µW under a temperature difference of 19 K in High relative contact electrical resistance and poor flexibility in inorganic thin-film thermoelectric devices significantly limit their practical applications. To overcome this challenge, a one-step thermal diffusion method to fabricate assembly-free inorganic thin-film thermoelectric devices is developed, where the in situ grown electrode delivers an excellent leg-electrode contact, leading to high output power and flexibility in the prepared p-type Sb 2 Te 3 /ntype Bi 2 Te 3 thin-film device, which is composed of 8 pairs of p-n junctions. Such a device shows a very low relative contact electrical resistance of 7.5% and a high power density of...

As an emerging semiconductor, environmentally friendly thermoelectric material, Cu2Se has drawn great attention due to its outstanding thermoelectric performance. In this work, Cu2Se-based thin films were deposited on a flexible polyimide substrate by magnetron sputtering technique via in-situ growth method. The effect of growth temperature and Cu composition was investigated. The results indicate that the thin films grown at 200 °C have high electrical conductivity due to their high carrier mobility. Further adjusting of Cu composition can achieve highly (0l0)-preferred orientation Cu2Se-based thin films with optimized carrier concentration, resulting in an increase in Seebeck coefficient and further leading to the enhancement of power factor.

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