Environment-Friendly Post-Treatment of PEDOT-Tos Films
by Aqueous Vitamin C Solutions for Tuning of Thermoelectric
EZAZ HASAN KHAN,
and JAYANT KUMAR
1.—Department of Chemistry, University of Massachusetts Lowell, Lowell, MA 01854, USA.
2.—Center for Advanced Materials, University of Massachusetts Lowell, Lowell, MA 01854, USA.
3.—Department of Physics, University of Massachusetts Lowell, Lowell, MA 01854, USA. 4.—US
Army Natick Soldier Research, Development and Engineering Center, Natick, MA 01760, USA.
Aqueous vitamin C solution has been used as an environment-friendly
reducing agent for tuning the thermoelectric properties of p-toluenesulfonate-
doped poly(3,4-ethylenedioxythiophene) (PEDOT-Tos) ﬁlms. The de-doping of
the PEDOT-Tos ﬁlms by aqueous vitamin C solutions led to a decrease in the
electrical conductivity of the ﬁlms. The measured ultraviolet-visible-near-in-
frared and x-ray photoelectron spectra clearly indicated the reduction in the
oxidation level from 37 to 23% when the PEDOT-Tos ﬁlms were treated with
5% (w/v) aqueous vitamin C solutions. An increase in the Seebeck coefﬁcient
was measured, resulting in an increase in the ﬁgure-of-merit (ZT). A 42%
increase in ZT was determined for the 5% aqueous vitamin C solution-treated
PEDOT-Tos ﬁlms with respect to that of the untreated ﬁlms.
Key words: Thermoelectric, oxidation state tuning, PEDOT-Tos, vitamin C,
electrical conductivity, Seebeck coefﬁcient
Inorganic-based thermoelectric materials and
their alloys have been extensively studied and
possess ﬁgure-of-merit (ZT) values greater than
However, these materials tend to be expen-
sive, are energy-intensive and rigid, and have
relatively high thermal conductivity.
organic conjugated polymer-based thermoelectric
materials offer some beneﬁcial properties such as
low thermal conductivity, readily available raw
materials, solution processability and ﬂexibility.
This has led to immense scientiﬁc interest for
research in the ﬁeld of conducting polymer-based
thermoelectric materials. However, the ZT value of
these materials is still low in comparison to that of
the inorganic-based materials,
where the quantity
ZT is given by S
rT/j, where S is the Seebeck
coefﬁcient, r is the electrical conductivity, j is the
thermal conductivity and T is the average absolute
temperature. A high ZT value is required for
polymer-based thermoelectric materials to be used
for practical applications.
ZT can be increased by
ﬁne tuning of one or more properties (S, r and j)of
the conducting polymers.
Among the various types of conducting polymers,
thiophene derivative-based polymeric materials
have shown promising results towards a high ZT
Fabrication of composite ﬁlms of poly
(PEDOT:PSS) mixed with inorganic materials has
led to an increase in r and an improvement in S.
ZT value of 0.42 was achieved for dimethyl sulfoxide
However, due to the
polymeric nature of the dopant, an excess of sulfonate
groups does not take part in the doping, thus acting as
an insulating phase.
(Received November 29, 2017; accepted March 29, 2018;
published online April 13, 2018)
Journal of ELECTRONIC MATERIALS, Vol. 47, No. 7, 2018
2018 The Minerals, Metals & Materials Society