3D Printing of Solution‐Processable 2D Nanoplates and 1D Nanorods for Flexible Thermoelectrics with Ultrahigh Power Factor at Low‐Medium Temperatures

Abstract

graphene, [10] conductive polymer, and hybrids, [11] have the ability to interconvert thermal to electrical energy without moving parts. These f-TEGs can be integrated with portable/wearable electronics and sensors, and enable selfpowered devices. In this context, V 2 -VI 3 metal chalcogenides (Bi 2 Te 3 , Sb 2 Te 3 , and related alloys and compounds) [1,[12][13][14][15][16][17] have attracted particular attention because of their high figure of merit (ZT) near room temperature. [18] For example, p-type Bi 2 Te 3 -Sb 2 Te 3 alloys show high performance near room temperature and benefit considerably from nanostructuring. [19] Similar to Bi 2 Te 3 , Sb 2 Te 3 is also a topological insulator, [20] which leads to a complex, nonparabolic band structure, often highly favorable for thermoelectric (TE) performance. [21] It has an extremely high dielectric constant of ε 0 ≈ 100, favorable for high mobility even with large concentration of defects. [22][23][24] Thus Sb 2 Te 3 is potentially an important TE material, the key challenge being to find methods to control its carrier concentration and to effectively nanostructure the material while maintaining this control. So far, most of the reported Sb 2 Te 3 related materials are p-type semiconductors. This is caused by intrinsic defects including Sb vacancies and antisite defects of Sb atoms on the Te sites (Sb Te ) [25] that occur during normal synthesis procedures. Typically, Sb 2 Te 3 bulk single crystals stand out for their unique advantages including a high electrical conductivity (σ) around 3-5 × 10 5 S m −1 , and a reasonable thermal conductivity (κ) around 1-6 W m −1 K −1 . However, Sb 2 Te 3 also has a less competitive Seebeck coefficient (S) around 83-105 µV K −1 . This is due to its high degenerate hole concentration (n > 10 20 cm −3 ) created by the acceptor states mentioned above, [26] especially Sb Te . Thus key problem is to find ways to control the doping level and thereby reduce the hole concentration and to determine the extent to which this can lead to enhanced S and TE performance. Nanostructuring has been employed to enhance S, and to reduce κ as a result of the increased phonon scattering effect. [19,[27][28][29][30] For example, Sb 2 Te 3 with 2D nanoplates morphology presents a 30% increase in S (S = 125 µV K −1 ) near room temperature. [31] S and ZT enhancement in nanostructured Solution-processable semiconducting 2D nanoplates and 1D nanorods are attractive building blocks for diverse technologies, including thermoelectrics, optoelectronics, and electronics. However, transforming colloidal nanoparticles into high-performance and flexible devices remains a challenge. For example, flexible films prepared by solution-processed semiconducting nanocrystals are typically plagued by poor thermoelectric and electrical transport properties. Here, a highly scalable 3D conformal additive printing approach to directly convert solution-processed 2D nanoplates and 1D nanorods into high-performing flexible devices is reported. The flexible films printed using Sb ...

Current advances and future perspectives of additive manufacturing for functional polymeric materials and devices

“…However, it is difficult to obtain complex shapes through conventional methods such as hot pressing, spark plasma sintering, and zone melting. 140 So far, SLA, 141 FDM, 142,143 SLS, 144 DIW, [145][146][147][148] SLM, [149][150][151][152] 3D printing technologies have been investigated for the preparation of TE devices.…”

Boosting the performance of printed thermoelectric materials by inducing morphological anisotropy

“…Many studies have reported inorganic TE slurries/powders that can be printed by SLM/SLS, 43,45,46 DIW [47][48][49] or stereolithography 50 to form ingots. Furthermore, the same materials can be formulated as inks, which can be directly painted onto 3D objects [51][52][53] or patterned on flexible substrates by inkjet printing, 42,54 aerosol jet printing, 53,55,56 dispensing, 57 or screen printing 52,[58][59][60][61][62][63][64] to form shape-conformable and flexible devices. However, the combination of those printing techniques with the search of morphological anisotropy to improve the final performance has been largely overlooked.…”

Synthesis and Performance of Large-Scale Cost-Effective Environment-Friendly Nanostructured Thermoelectric Materials

“…Ou et al fabricated a TEG made from Sb 2 Te 3 nanoflakes and carbon nanotubes with a power factor of ≈41 μWm −1 K −2 using a modified aerosol-jet printing method [ 96 ]. Dun et al used this 3D conformal aerosol printing of solution-processed p-type Sb 2 Te 3 to print flexible TEG with a high power factor of 2.2 mWm −1 K −2 at 500 K [ 97 ]. Figure 10 illustrates the 3D aerosol jet printing of p-type Sb 2 Te 3 .…”

“… Schematic illustration of aerosol printing. Reproduced with permission from [ 97 ]. Copyright Wiley Online Library, 2019.…”