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Acidity-Controlled Conducting Polymer Films for Organic Thermoelectric Devices with Horizontal and Vertical Architectures

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ABSTRACT

Organic thermoelectric devices (OTEDs) are recognized one of the next generation energy conversion platforms because of their huge potentials for securing electricity continuously from even tiny heat sources in our daily life. The advantage of OTEDs can be attributable to the design freedom in device shapes and the low-cost fabrication by employing solution coating processes at low temperatures. As one of the major OTE materials to date, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) has been used, but no study has been yet carried out on its acidity control even though the acidic components in OTEDs can seriously affect the device performance upon operation. Here we demonstrate that the addition of aniline (a weak base) can control the acidity of PEDOT:PSS and enhance the performance of OTEDs. In particular, the vertical OTEDs with aniline-doped PEDOT:PSS films (active area = 1.0 cm2) could continuously generate electricity (0.06 nW) even at low temperatures (<38 °C) when they were mounted on a desk lamp (power = 24 W).

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(a) Scheme for the aniline (ANL) doping to the free sulfonic acid groups in the PSS units of PEDOT:PSS. (b) Solutions and films of PEDOT:PSS according to the amount of aniline (RA/P = 0, 1.5, and 5). (c) Optical absorption spectra of films according to the amount of aniline (RA/P = 0, 1.5, and 5) (inset: normalized transmittance). (d) Device structures for horizontal (planar) OTEDs which are fabricated with the ITO-glass substrates. (e) Device structures for vertical (single stacked) OTEDs which are fabricated with the Cu-foil substrates.
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f1: (a) Scheme for the aniline (ANL) doping to the free sulfonic acid groups in the PSS units of PEDOT:PSS. (b) Solutions and films of PEDOT:PSS according to the amount of aniline (RA/P = 0, 1.5, and 5). (c) Optical absorption spectra of films according to the amount of aniline (RA/P = 0, 1.5, and 5) (inset: normalized transmittance). (d) Device structures for horizontal (planar) OTEDs which are fabricated with the ITO-glass substrates. (e) Device structures for vertical (single stacked) OTEDs which are fabricated with the Cu-foil substrates.

Mentions: In order to control the acidity of PEDOT:PSS, aniline (ANL) was added to the PEDOT:PSS solutions by varying the molar ratio (RA/P) of ANL to the free acidic part (PSS) of PEDOT:PSS. As shown in Fig. 1a, the aniline molecules react with the sulfonic acid groups, which remain freely in the PSS part without involving the doping reaction to the PEDOT parts, by acid-base reactions in solutions. As a result, the free sulfonic acid groups are neutralized with aniline via the proton shift to the aniline from the sulfonic acid groups. Because aniline has a weak yellowish color, the solution color seems to be unchanged even after reaction with a small amount of aniline (see Fig. 1b). However, the film color was slightly changed from bluish to greenish one with increasing the aniline content, which reflects the direct influence of aniline addition as supported from the optical absorption spectra (see Fig. 1c). As shown in Fig. 1d,e, two different types of device geometry (architecture) were introduced in order to examine the thermoelectric performance of the aniline-doped PEDOT:PSS (PEDOT:PSS_ANL) films. The horizontal (planar) geometry is effective in terms of fabrication process because OTEDs can be easily made by just coating the PEDOT:PSS_ANL films on the pre-patterned electrodes (Fig. 1d) but it has a demerit in practical applications because of difficulty in separate mounting of electrodes on either hot or cool region of heat sources. In contrast, the vertical (stacked) geometry is practical for real applications even though OTEDs should be fabricated by stacking the PEDOT:PSS_ANL films in between bottom and top electrodes (Fig. 1e).


Acidity-Controlled Conducting Polymer Films for Organic Thermoelectric Devices with Horizontal and Vertical Architectures
(a) Scheme for the aniline (ANL) doping to the free sulfonic acid groups in the PSS units of PEDOT:PSS. (b) Solutions and films of PEDOT:PSS according to the amount of aniline (RA/P = 0, 1.5, and 5). (c) Optical absorption spectra of films according to the amount of aniline (RA/P = 0, 1.5, and 5) (inset: normalized transmittance). (d) Device structures for horizontal (planar) OTEDs which are fabricated with the ITO-glass substrates. (e) Device structures for vertical (single stacked) OTEDs which are fabricated with the Cu-foil substrates.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5035924&req=5

f1: (a) Scheme for the aniline (ANL) doping to the free sulfonic acid groups in the PSS units of PEDOT:PSS. (b) Solutions and films of PEDOT:PSS according to the amount of aniline (RA/P = 0, 1.5, and 5). (c) Optical absorption spectra of films according to the amount of aniline (RA/P = 0, 1.5, and 5) (inset: normalized transmittance). (d) Device structures for horizontal (planar) OTEDs which are fabricated with the ITO-glass substrates. (e) Device structures for vertical (single stacked) OTEDs which are fabricated with the Cu-foil substrates.
Mentions: In order to control the acidity of PEDOT:PSS, aniline (ANL) was added to the PEDOT:PSS solutions by varying the molar ratio (RA/P) of ANL to the free acidic part (PSS) of PEDOT:PSS. As shown in Fig. 1a, the aniline molecules react with the sulfonic acid groups, which remain freely in the PSS part without involving the doping reaction to the PEDOT parts, by acid-base reactions in solutions. As a result, the free sulfonic acid groups are neutralized with aniline via the proton shift to the aniline from the sulfonic acid groups. Because aniline has a weak yellowish color, the solution color seems to be unchanged even after reaction with a small amount of aniline (see Fig. 1b). However, the film color was slightly changed from bluish to greenish one with increasing the aniline content, which reflects the direct influence of aniline addition as supported from the optical absorption spectra (see Fig. 1c). As shown in Fig. 1d,e, two different types of device geometry (architecture) were introduced in order to examine the thermoelectric performance of the aniline-doped PEDOT:PSS (PEDOT:PSS_ANL) films. The horizontal (planar) geometry is effective in terms of fabrication process because OTEDs can be easily made by just coating the PEDOT:PSS_ANL films on the pre-patterned electrodes (Fig. 1d) but it has a demerit in practical applications because of difficulty in separate mounting of electrodes on either hot or cool region of heat sources. In contrast, the vertical (stacked) geometry is practical for real applications even though OTEDs should be fabricated by stacking the PEDOT:PSS_ANL films in between bottom and top electrodes (Fig. 1e).

View Article: PubMed Central - PubMed

ABSTRACT

Organic thermoelectric devices (OTEDs) are recognized one of the next generation energy conversion platforms because of their huge potentials for securing electricity continuously from even tiny heat sources in our daily life. The advantage of OTEDs can be attributable to the design freedom in device shapes and the low-cost fabrication by employing solution coating processes at low temperatures. As one of the major OTE materials to date, poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) has been used, but no study has been yet carried out on its acidity control even though the acidic components in OTEDs can seriously affect the device performance upon operation. Here we demonstrate that the addition of aniline (a weak base) can control the acidity of PEDOT:PSS and enhance the performance of OTEDs. In particular, the vertical OTEDs with aniline-doped PEDOT:PSS films (active area = 1.0 cm2) could continuously generate electricity (0.06 nW) even at low temperatures (<38 °C) when they were mounted on a desk lamp (power = 24 W).

No MeSH data available.