Enhanced Power Factor of PEDOT:PSS Films Post-treated Using a Combination of Ethylene Glycol and Metal Chlorides and Temperature Dependence of Electronic Transport (325–450 K)

Abstract

We report temperature dependence of electrical c o n d u c t i v i t y a n d t h e r m o p o w e r f o r p o l y ( 3 , 4ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) thin films post-treated using a combination of an organic polar solvent of ethylene glycol (EG) and transition metal chlorides. The pristine and post-treated PEDOT:PSS films are characterized by X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), atomic force microscopy (AFM), Raman spectroscopy techniques, and Hall effect measurements. Structural changes are confirmed by crystallinity improvement and Raman shift of the PEDOT:PSS, which correlate with a significant enhancement in thermoelectric power factor. The large variation of electronic transport in these films post-treated with three different metal chlorides can be attributed to the complex contribution of different conduction pathways. Among post-treated films, the highest electrical conductivity and power factor are attained for the EG/1 M ZnCl 2 post-treated PEDOT:PSS film with 1979 S/cm and 132 μW/m K 2 at 375 K. In general, organic conductive polymers have very low thermal conductivity; a zT = 0.24 at 375 K could be attained by assuming a thermal conductivity of 0.2 W/m-K. These results indicate that a combination of polar organic solvent EG and metal chlorides to post-treat a PEDOT:PSS film is a promising approach to enhance the thermoelectric properties of the conductive polymers of PEDOT:PSS.

High Performance of Post-Treated PEDOT:PSS Thin Films for Thermoelectric Power Generation Applications

“…The Hall carrier concentration increases from 1.79 × 10 18 cm –3 for the pristine film to 9.52 × 10 20 cm –3 for the EG-treated film. For the films post-treated with various concentrations of EG/NaBH 4 or EG/NaHCO 3 solution, the σ decreases with increasing concentration, ,, which correlates well with the decreasing carrier concentration as shown in Table . The magnitude of σ for the post-treated PEDOT:PSS films from 325 to 450 K lies in the ranges of 1215 and 970 S/cm, 1206 and 947 S/cm, 1132 and 923 S/cm, 943 and 564 S/cm, and 555 and 257 S/cm using 0.01, 0.05, 0.1, 0.5, and 1 M EG/NaBH 4 , respectively; and 957 and 848 S/cm, 895 and 770 S/cm, 614 and 509 S/cm, 555 and 339 S/cm, and 547 and 146 S/cm using 0.01, 0.05, 0.1, 0.5, and 1 M EG/NaHCO 3 , respectively.…”

“…The insulating PSS chains decorated with the conducting PEDOT embrace a necklace structure in water and are the energy barrier for the electronic transport through the PEDOT chains, which leads to localization of the charge carriers on the conducting chains and hence low electrical conductivity of the pristine PEDOT:PSS films. Immanuel et al 37 reported enhancement of the power factor by using a combination of EG and metal chlorides in post-treated PEDOT:PSS films. The enhancement is partially attributed to the structural changes leading to a significant increase of electrical conductivity.…”

Ultraflexible PEDOT:PSS/Helical Carbon Nanotubes Film for All-in-One Photothermoelectric Conversion

“…The first peak of the pristine PEDOT:PSS film, which is located at 6.59°, is assigned to the second reflection of the interlamella between the side by side PEDOT lamella (PEDOT alternated d (200) , marked by a blue dashed line in Figure d). The diffraction peak at 11.15° is attributed to the alternate lamella stacking of PSS and PSS , (PSS alternated d (100) ) at which PEDOT lamellas are sandwiched in the gap. The third peak at 13.67° is related to the neighboring PSS lamella , (PSS neighboring d (100) ), which has no PEDOT molecular inner gap.…”

“…The diffraction peak at 11.15° is attributed to the alternate lamella stacking of PSS and PSS , (PSS alternated d (100) ) at which PEDOT lamellas are sandwiched in the gap. The third peak at 13.67° is related to the neighboring PSS lamella , (PSS neighboring d (100) ), which has no PEDOT molecular inner gap. The peak at 17.28° corresponds to the PSS benzene ring π–π stacking (PSS π–π stacking d (001) , marked by a orange dashed line).…”

Additive Effect on the Structure of PEDOT:PSS Dispersions and Its Correlation with the Structure and Morphology of Thin Films

“…In organic solar cells, PEDOT:PSS is prominent as the hole-extracting layer, enhancing the work function in comparison with the usual transparent electrode indium tin oxide (ITO) and improving the contact between the electrode and the active layer [ 5 ]. It is also used in perovskite solar cells [ 6 ], OLEDs [ 7 ], OFETs [ 8 ], and thermoelectrics [ 9 ]. Different oxidation levels lead to changes in the visible absorption spectra of PEDOT:PSS, making it suitable for electrochromic windows [ 10 ].…”