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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).

No MeSH data available.


(a) Thermoelectric (TE) characteristics (voltage, current, power, and Seebeck coefficient (S)) of horizontal (planar) OTEDs with the 70 nm-thick PEDOT:PSS_ANL films according to the aniline ratio (RA/P) as a function of temperature difference. (b) TE characteristics as a function of RA/P at ΔT = 50 K.
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f3: (a) Thermoelectric (TE) characteristics (voltage, current, power, and Seebeck coefficient (S)) of horizontal (planar) OTEDs with the 70 nm-thick PEDOT:PSS_ANL films according to the aniline ratio (RA/P) as a function of temperature difference. (b) TE characteristics as a function of RA/P at ΔT = 50 K.

Mentions: The planar OTEDs with the thin PEDOT:PSS_ANL films (thickness = 70 nm) were fabricated using the patterned ITO-glass substrates (see Fig. 1d). As shown in Fig. 3a (top), the device voltage was gradually increased in the negative direction for all devices as the temperature increased. In particular, the voltage (absolute value) at a fixed temperature difference (ΔT) was higher for the OTEDs with the PEDOT:PSS_ANL films than the control device with the pristine PEDOT:PSS film. The voltage difference at ΔT = 50 °C is summarized in Fig. 3b (top), which delivers the highest voltage at RA/P = 1.5. Similar to the voltage trend, all OTEDs showed the negatively increased current with the temperature in the presence of obvious current difference according to the aniline content (Fig. 3a middle top). The highest (negative) current (−2.224 μA) at ΔT = 50 °C was measured at RA/P = 1.5, which is the same as for the voltage trend, even though only −0.002 μA was measured for the control device. This result indicates that the device performance could be significantly enhanced by the aniline addition. However, more than RA/P = 1.5 led to adverse effect because both voltage and current were gradually decreased with the aniline content. As a consequence, the highest electrical power could be generated at RA/P = 1.5 over the entire temperature range tested in this work (see the power factor trend in Table S1). A particular attention is paid to the electrical power trend that exhibits the higher power generation at the higher temperature, which is partly supported by the trend of Seebeck coefficient for the OTEDs with the PEDOT:PSS_ANL films that are clearly outperforming the control device (see Fig. 3 bottom). The reason for such improvement in device performances can be attributed to the enhanced electrical conductivity of PEDOT:PSS films by the addition of aniline (see Fig. S3). The highest electrical conductivity in the in-plane direction of films was measured at RA/P = 1.5, which can be correlated with the finer morphology leading to the improved contact among the intrinsic PEDOT:PSS nanoparticles with better conjugation lengths at RA/P = 1.5 (see Fig. 2e). Interestingly, the electrical conductivity was slightly more increased with temperature for the PEDOT:PSS_ANL films up to RA/P = 2 but it followed the trend of the pristine PEDOT:PSS at RA/P = 5. This result informs that too much aniline addition has an adverse effect on the electrical properties owing to the morphology change as discussed in Fig. 2e.


Acidity-Controlled Conducting Polymer Films for Organic Thermoelectric Devices with Horizontal and Vertical Architectures
(a) Thermoelectric (TE) characteristics (voltage, current, power, and Seebeck coefficient (S)) of horizontal (planar) OTEDs with the 70 nm-thick PEDOT:PSS_ANL films according to the aniline ratio (RA/P) as a function of temperature difference. (b) TE characteristics as a function of RA/P at ΔT = 50 K.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f3: (a) Thermoelectric (TE) characteristics (voltage, current, power, and Seebeck coefficient (S)) of horizontal (planar) OTEDs with the 70 nm-thick PEDOT:PSS_ANL films according to the aniline ratio (RA/P) as a function of temperature difference. (b) TE characteristics as a function of RA/P at ΔT = 50 K.
Mentions: The planar OTEDs with the thin PEDOT:PSS_ANL films (thickness = 70 nm) were fabricated using the patterned ITO-glass substrates (see Fig. 1d). As shown in Fig. 3a (top), the device voltage was gradually increased in the negative direction for all devices as the temperature increased. In particular, the voltage (absolute value) at a fixed temperature difference (ΔT) was higher for the OTEDs with the PEDOT:PSS_ANL films than the control device with the pristine PEDOT:PSS film. The voltage difference at ΔT = 50 °C is summarized in Fig. 3b (top), which delivers the highest voltage at RA/P = 1.5. Similar to the voltage trend, all OTEDs showed the negatively increased current with the temperature in the presence of obvious current difference according to the aniline content (Fig. 3a middle top). The highest (negative) current (−2.224 μA) at ΔT = 50 °C was measured at RA/P = 1.5, which is the same as for the voltage trend, even though only −0.002 μA was measured for the control device. This result indicates that the device performance could be significantly enhanced by the aniline addition. However, more than RA/P = 1.5 led to adverse effect because both voltage and current were gradually decreased with the aniline content. As a consequence, the highest electrical power could be generated at RA/P = 1.5 over the entire temperature range tested in this work (see the power factor trend in Table S1). A particular attention is paid to the electrical power trend that exhibits the higher power generation at the higher temperature, which is partly supported by the trend of Seebeck coefficient for the OTEDs with the PEDOT:PSS_ANL films that are clearly outperforming the control device (see Fig. 3 bottom). The reason for such improvement in device performances can be attributed to the enhanced electrical conductivity of PEDOT:PSS films by the addition of aniline (see Fig. S3). The highest electrical conductivity in the in-plane direction of films was measured at RA/P = 1.5, which can be correlated with the finer morphology leading to the improved contact among the intrinsic PEDOT:PSS nanoparticles with better conjugation lengths at RA/P = 1.5 (see Fig. 2e). Interestingly, the electrical conductivity was slightly more increased with temperature for the PEDOT:PSS_ANL films up to RA/P = 2 but it followed the trend of the pristine PEDOT:PSS at RA/P = 5. This result informs that too much aniline addition has an adverse effect on the electrical properties owing to the morphology change as discussed in Fig. 2e.

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.