Abstract
ABSTRACT Printed electronics implies the use of low-cost, scalable, printing technologies to fabricate electronic devices and circuits on flexible substrates, such as paper or plastics. The development of this new electronic is currently expanding because of the emergence of the internet-of-everything. Although lot of attention has been paid to functional inks based on organic semiconductors, another class of inks is based on nanoparticles obtained from exfoliated 2D materials, such as graphene and metal sulfides. The ultimate scientific and technological challenge is to find a strategy where the exfoliated nanoparticle flakes in the inks can, after solvent evaporation, form a solid which displays performances equal to the single crystal of the 2D material. In this context, a printed layer, formed from an ink composed of nano-flakes of TiS2 intercalated with hexylamine, which displays thermoelectric properties superior to organic intercalated TiS2 single crystals, is demonstrated for the first time. The choice of the fraction of exfoliated nano-flakes appears to be a key to the forming of a new self-organized layered material by solvent evaporation. The printed layer is an efficient n-type thermoelectric material which complements the p-type printable organic semiconductors The thermoelectric power factor of the printed TiS2/hexylamine thin films reach record values of 1460 µW m−1 K−2 at 430 K, this is considerably higher than the high value of 900 µW m−1 K−2 at 300 K reported for a single crystal. A printed thermoelectric generator based on eight legs of TiS2 confirms the high-power factor values by generating a power density of 16.0 W m−2 at ΔT = 40 K.
Highlights
The interest for printable and flexible thermoelectric devices has increased in recent years as a result of many potential applications such as wearable energy harvesting [1,2,3,4,5,6,7], the powering of wireless sensors for the internet-of-everything [8,9], ultra-sensitive ther mopiles [10], etc
P-type printed thermoelectric devices based on organic semi conductors have achieved reasonable performances [11,12]. zTs values in the range of 0.3–0.4 at room temperature were obtained with the polymer poly (3,4-ethylenedioxy-thiophene):polystyrene sulfonic acid (PEDOT:PSS) by tuning its level of doping [13,14]
TiS2 was recently used to prepare new n-type hybrid TiS2/organic superlattice materials as efficient n-type counterparts to the printed p-type PEDOT:PSS films. This choice of n- and p-type thermoelectric materials is today the most promising for the fabrica tion of efficient thermoelectric generators based on printing processes without high-temperature treat ments, i.e. enabling a range of flexible substrates such as paper and plastics which are crucial in packaging and their further implementation in the internet-ofeverything [21]
Summary
The interest for printable and flexible thermoelectric devices has increased in recent years as a result of many potential applications such as wearable energy harvesting [1,2,3,4,5,6,7], the powering of wireless sensors for the internet-of-everything [8,9], ultra-sensitive ther mopiles [10], etc. On the other hand n-type exfoliated inorganic thermoelectric materials based on metal chalcogenide compounds were considered as promising, due to their low cost, environmental friendliness and the high reported power factor of their bulk form [18,19,20] One of these compounds, TiS2 was recently used to prepare new n-type hybrid TiS2/organic superlattice materials as efficient n-type counterparts to the printed p-type PEDOT:PSS films. The power factor was more than 4 times lower than the intercalated TiS2 single crystal, these studies demon strated the potential of solution process for fabricating 2D thermoelectric inorganic nanomaterial layers This technology based on hybrid intercalated TiS2 materials was the subject of patent applications [29,30]. This work paves the way for a possible replication of multiple patterns of p- and n-legs by printing technol ogies; which is required to reach the thermo-voltage up to useful values in electronics (order of 1 volt)
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