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

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).

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(a) Acidity of the PEDOT:PSS solutions according to the aniline ratio (RA/P). (b) Work functions of the PEDOT:PSS_ANL films according to the aniline ratio (RA/P). (c) Raman spectra of the PEDOT:PSS_ANL films according to the aniline ratio (RA/P): Cβ-Cβ stretching vibration at ca. 1370 cm−1, symmetric Cα-Cβ stretching vibration at ca. 1440 cm−1, and asymmetric Cα-Cβ stretching vibration at ca. 1500 cm−1. (d) XPS spectra of the PEDOT:PSS_ANL films according to the aniline ratio (RA/P): (left) S2p, (right) O1s. (e) AFM images (top: height mode, bottom: phase mode) for the PEDOT:PSS_ANL films according to the aniline ratio (RA/P): The small images on top were taken from the parts marked with the dotted circles in the height mode images. The root-mean-square roughness (Rg) is given on each image.
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f2: (a) Acidity of the PEDOT:PSS solutions according to the aniline ratio (RA/P). (b) Work functions of the PEDOT:PSS_ANL films according to the aniline ratio (RA/P). (c) Raman spectra of the PEDOT:PSS_ANL films according to the aniline ratio (RA/P): Cβ-Cβ stretching vibration at ca. 1370 cm−1, symmetric Cα-Cβ stretching vibration at ca. 1440 cm−1, and asymmetric Cα-Cβ stretching vibration at ca. 1500 cm−1. (d) XPS spectra of the PEDOT:PSS_ANL films according to the aniline ratio (RA/P): (left) S2p, (right) O1s. (e) AFM images (top: height mode, bottom: phase mode) for the PEDOT:PSS_ANL films according to the aniline ratio (RA/P): The small images on top were taken from the parts marked with the dotted circles in the height mode images. The root-mean-square roughness (Rg) is given on each image.

Mentions: As shown in Fig. 2a, the acidity of PEDOT:PSS (aqueous solution) was gradually changed from pH = 1.74 to pH = 6.1 as the aniline content increased. A slow pH increase was measured up to RA/P = 1.4, followed by the swift change in pH value between RA/P = 1.4 and RA/P = 2.2. After RA/P = 2.2, the increasing trend was quite slowed down leading to pH = 5.29 at RA/P = 5. These results inform that the acidity of PEDOT:PSS can be effectively controlled with aniline. Interestingly, the work function of films was noticeably affected by the addition of aniline (see Fig. 2b). When the same amount of aniline to the PSS monomeric unit with free sulfonic acid group (RA/P = 1.0) was added, the work function was noticeably shifted from −5.2 eV to −5.0 eV. However, further addition of aniline did not almost change the work function, which indicates that the electronic properties of PEDOT:PSS are initially (RA/P = 1.0) influenced but insensitive to the presence of more aniline even though the acidity of solutions was greatly affected as discussed in Fig. 2a. This trend is also supported by the Raman spectra on the vibration of thiophene rings in the PEDOT units (Fig. 2c), which deliver clear shift to the low wavenumber direction at RA/P = 1.0 compared to the pristine PEDOT:PSS film (RA/P = 0) but no further shift was made with additional aniline ratios. In particular, it is considered that more π-conjugations through the PEDOT chains could be made by the addition of aniline because the Raman peak (symmetric Cα-Cβ stretching vibration) at ca. 1440 cm−1 (benzenoid structure) was shifted to ca. 1415 cm−1 (quinoid structure)3435363738.


Acidity-Controlled Conducting Polymer Films for Organic Thermoelectric Devices with Horizontal and Vertical Architectures
(a) Acidity of the PEDOT:PSS solutions according to the aniline ratio (RA/P). (b) Work functions of the PEDOT:PSS_ANL films according to the aniline ratio (RA/P). (c) Raman spectra of the PEDOT:PSS_ANL films according to the aniline ratio (RA/P): Cβ-Cβ stretching vibration at ca. 1370 cm−1, symmetric Cα-Cβ stretching vibration at ca. 1440 cm−1, and asymmetric Cα-Cβ stretching vibration at ca. 1500 cm−1. (d) XPS spectra of the PEDOT:PSS_ANL films according to the aniline ratio (RA/P): (left) S2p, (right) O1s. (e) AFM images (top: height mode, bottom: phase mode) for the PEDOT:PSS_ANL films according to the aniline ratio (RA/P): The small images on top were taken from the parts marked with the dotted circles in the height mode images. The root-mean-square roughness (Rg) is given on each image.
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Related In: Results  -  Collection

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Show All Figures
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f2: (a) Acidity of the PEDOT:PSS solutions according to the aniline ratio (RA/P). (b) Work functions of the PEDOT:PSS_ANL films according to the aniline ratio (RA/P). (c) Raman spectra of the PEDOT:PSS_ANL films according to the aniline ratio (RA/P): Cβ-Cβ stretching vibration at ca. 1370 cm−1, symmetric Cα-Cβ stretching vibration at ca. 1440 cm−1, and asymmetric Cα-Cβ stretching vibration at ca. 1500 cm−1. (d) XPS spectra of the PEDOT:PSS_ANL films according to the aniline ratio (RA/P): (left) S2p, (right) O1s. (e) AFM images (top: height mode, bottom: phase mode) for the PEDOT:PSS_ANL films according to the aniline ratio (RA/P): The small images on top were taken from the parts marked with the dotted circles in the height mode images. The root-mean-square roughness (Rg) is given on each image.
Mentions: As shown in Fig. 2a, the acidity of PEDOT:PSS (aqueous solution) was gradually changed from pH = 1.74 to pH = 6.1 as the aniline content increased. A slow pH increase was measured up to RA/P = 1.4, followed by the swift change in pH value between RA/P = 1.4 and RA/P = 2.2. After RA/P = 2.2, the increasing trend was quite slowed down leading to pH = 5.29 at RA/P = 5. These results inform that the acidity of PEDOT:PSS can be effectively controlled with aniline. Interestingly, the work function of films was noticeably affected by the addition of aniline (see Fig. 2b). When the same amount of aniline to the PSS monomeric unit with free sulfonic acid group (RA/P = 1.0) was added, the work function was noticeably shifted from −5.2 eV to −5.0 eV. However, further addition of aniline did not almost change the work function, which indicates that the electronic properties of PEDOT:PSS are initially (RA/P = 1.0) influenced but insensitive to the presence of more aniline even though the acidity of solutions was greatly affected as discussed in Fig. 2a. This trend is also supported by the Raman spectra on the vibration of thiophene rings in the PEDOT units (Fig. 2c), which deliver clear shift to the low wavenumber direction at RA/P = 1.0 compared to the pristine PEDOT:PSS film (RA/P = 0) but no further shift was made with additional aniline ratios. In particular, it is considered that more π-conjugations through the PEDOT chains could be made by the addition of aniline because the Raman peak (symmetric Cα-Cβ stretching vibration) at ca. 1440 cm−1 (benzenoid structure) was shifted to ca. 1415 cm−1 (quinoid structure)3435363738.

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.


Related in: MedlinePlus