Engineered doping of organic semiconductors for enhanced thermoelectric efficiency

Abstract

Significant improvements to the thermoelectric figure of merit ZT have emerged in recent years, primarily due to the engineering of material composition and nanostructure in inorganic semiconductors (ISCs). However, many present high-ZT materials are based on low-abundance elements that pose challenges for scale-up, as they entail high material costs in addition to brittleness and difficulty in large-area deposition. Here we demonstrate a strategy to improve ZT in conductive polymers and other organic semiconductors (OSCs) for which the base elements are earth-abundant. By minimizing total dopant volume, we show that all three parameters constituting ZT vary in a manner so that ZT increases; this stands in sharp contrast to ISCs, for which these parameters have trade-offs. Reducing dopant volume is found to be as important as optimizing carrier concentration when maximizing ZT in OSCs. Implementing this strategy with the dopant poly(styrenesulphonate) in poly(3,4-ethylenedioxythiophene), we achieve ZT = 0.42 at room temperature.

Organic π-type thermoelectric module supported by photolithographic mold: a working hypothesis of sticky thermoelectric materials

“…As is the tendency of conductive polymers, the dedoped PEDOT:PSS first enhanced the S and decreased the σ due to the decrease in the carrier concentration. Similar to the immersed case [9], however, both the S and the σ were enhanced in the region from pH 4 to pH 8, which can be explained by the removed PSS shortening electron-tunneling distance between the conductive PEDOT chains and enhancing the carrier mobility. In total, the dedoped PEDOT:PSS improved the PF from 0.275 µW/mK 2 at pH 1 to 0.336 µW/mK 2 at pH 8.…”

“…In total, the dedoped PEDOT:PSS improved the PF from 0.275 µW/mK 2 at pH 1 to 0.336 µW/mK 2 at pH 8. To recover the σ , we further added DMSO to the dedoped PEDOT:PSS, where DMSO was expected to align the PEDOT conductive chains [9]. Although it did not affect the S , DMSO improved the σ and reached 3.45 µW/mK 2 in the PF (Figure 6; see the details in Table S3).…”

“…In contrast, flexibility of organic TE modules allows the economic mass-production, for example, using roll-to-roll processes, because the flexible TE modules can adjust their shapes to fit various heat elements even after being mass-produced. Although the difficulty in the measurement of in-plain thermal conductivity of organic films may raise some question of the accuracy [7], the TE figure of merit ( ZT ) of organic materials has been reported to reach up to 0.42, recently [2,8,9]. ZT is given as: …”

“…Although dedoping of PSS yielded ZT  = 0.42 in PEDOT:PSS [9], the demonstrated process cannot be implemented as an economic mass-production process because the spin-cast PEDOT:PSS must be immersed once in ethylene glycol for 1 h for every 20–125 nm deposition; the organic TE legs need at least 20 µm thickness to maintain the internal Δ T . Therefore, we also examine dedoping of PSS using an anion absorbent, where the anionic sulfonic group of PSS should be captured in a mixture solution with the anion absorbent before being injected into the photolithographic mold.…”

Transparent Wood Smart Windows: Polymer Electrochromic Devices Based on Poly(3,4‐Ethylenedioxythiophene):Poly(Styrene Sulfonate) Electrodes

“…Without modification, PEDOT:PSS films exhibit a relatively low conductivity of 0.1–1 S cm −1 because of the large excess of inactive PSS − inhibiting charge transport between PEDOT + crystallites. The conductivity of PEDOT:PSS has been enhanced by orders of magnitude to well over 1000 S cm −1 through the incorporation of co‐solvents or by post treatments with strong acids 42, 43, 44, 45. This enhancement is attributed to a higher degree of ordering and increased domain purity of the PEDOT + crystallites combined with a partial removal of excess PSS − .…”