Enhancement of the thermoelectric properties of PEDOT:PSS thin films by post-treatment

Abstract

In this work, the thermoelectric (TE) properties of poly(3,4- ethylenedioxylthiophene):poly(styrene sulfonate) (PEDOT:PSS) thin films at room temperature are studied. Different methods have been applied for tuning the TE properties: 1st addition of polar solvent, dimethyl sulfoxide (DMSO), into the PEDOT:PSS solution; 2nd post-treatment of thin films with a mixture of DMSO and ionic liquid, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4). It is verified that DMSO post-treatment is more efficient than DMSO addition in improving the electrical conductivity with a trivial change in the Seebeck coefficient. The power factor is increased up to 30.1 W mK-2 for the film with DMSO post-treatment, while the optimized power factor by DMSO addition is 18.2 W mK-2. It is shown that both DMSO addition and post-treatment induce morphological changes: an interconnected network of elongated PEDOT grains is generated, leading to higher electrical conductivity. In contrast, for t hose films post-treated in the presence of EMIMBF4, an interconnected network of short and circular PEDOT grains with increased polaron density is created, resulting in the improvement in the Seebeck coefficient and a concomitant compromise in the electrical conductivity. An optimized power factor of 38.46 W mK -2 is achieved at 50 vol% of EMIMBF4, which is the highest reported so far for PEDOT:PSS thin films to our knowledge. Assuming a thermal conductivity of 0.17 W mK-1, the corresponding ZT is 0.068 at 300 K. These results demonstrate that post-treatment is a promising approach to enhance the TE properties of PEDOT:PSS thin films. Furthermore, ionic liquid, EMIMBF4, shows the potential for tuning the TE properties of PEDOT:PSS thin films via a more environmentally benign process

Flexible and conductive multilayer films based on the assembly of PEDOT:PSS and water soluble polythiophenes

“…For drop casted films, Seebeck coefficient is equal to 1200 µV.K -1 for P3HT-Im and to 26.0 µV.K -1 for PEDOT:PSS. These coefficients are in agreement with those reported in the literature [53][54][55].…”

Effective Approaches to Improve the Electrical Conductivity of PEDOT:PSS: A Review

“…[ 72 ] It has been reported by Luo and coworkers that DMSO post-treatment of PEDOT:PSS (Clevios PH 1000) is much more effi cient than DMSO addition for the improvement of conductivity. [ 73 ] In contrary, Unsworth et al indicated that both DMSO addition and immersion treatments improve the conductivity of the PEDOT:PSS (Clevios PH 1000) by a similar magnitude. [ 74 ] Ouyang's group have systematically investigated PEDOT:PSS fi lms post-treated with geminal diols which have two hydroxyl groups connected to one carbon atom or amphiphilic fl uoro compounds which have hydrophobic fl uorocarbon groups and hydrophilic hydroxyl or carboxylic groups, for example, hexafl uoroacetone (HFA), cyclohexanehexone, formaldehyde, acetaldehyde, and perfl uorobenzophenone.…”

Optimizing the thermoelectric properties of PEDOT:PSS films by combining organic co-solvents with inorganic base

“…In 2008, our group firstly reported the thermoelectric performance of PEDOT:PSS, drawing a new research hotspot in the field of organic TE materials [11]. In spite of the intrinsic advantages of PEDOT:PSS, the conflicting combination among the electrical conductivity, Seebeck coefficient and the thermal conductivity imposes limitations on the optimization of ZT, hence its TE efficiency, however to date, is still much lower than that of inorganic semiconductor-based TE devices [5,14,15]. To obtain an excellent ZT value at room temperature, in addition to its intrinsic low thermal conductivity, a high power factor is also of key importance.…”

“…3rd, simultaneous enhancement in the electrical conductivity and Seebeck coefficient by post-treatment, mixing approach or blending with inorganic materials etc. [12,14,[22][23][24]. 4th, optimization of power factor by controlling the redox level of PEDOT chains through a dedoping process [25][26][27].…”