Neutral, Polaron, and Bipolaron States in PEDOT Prepared by Photoelectrochemical Polymerization and the Effect on Charge Generation Mechanism in the Solid-State Dye-Sensitized Solar Cell

Abstract

We investigate dye-sensitized solar cells (DSSCs) based on PEDOT as hole conductor and prepared by photoelectrochemical polymer deposition at different light intensities. We specifically investigate the effect of light intensity on the PEDOT polymer and in turn the efficiency of the solar cells. We find that the PEDOT prepared by this method is largely oxidized and contains significant amounts of polarons and bipolarons and only a small fraction of neutral PEDOT. Photoelectrochemical polymer deposition under low light intensity leads to a particularly low fraction of neutral PEDOT and a high fraction of bipolarons as measured in the UV–vis spectra. The solar cells based on PEDOT as a hole conductor prepared under these conditions are the most efficient with a higher power conversion efficiency, which can be explained by a longer electron lifetime, faster charge transport, and higher transparency of the PEDOT. Interestingly, we conclude that in this type of solid-state DSSCs the mechanism of dye regeneration occurs from PEDOT polarons that then form bipolarons, which is different from the mechanism of dye regeneration proposed in standard solid-state DSSCs.

A conductive stretchable PEDOT–elastomer hybrid with versatile processing and properties

“…17 It appears that this lets the material to absorb the oxidant solution deeper into its structure, allowing the subsequent VPP to create a more extensive PEDOT network. UV--vis absorption profiles indicate the formation of conductive PEDOT, 18,19 with this correlated to the PGS cure time ( fig. S2).…”

Stability of poly(3,4-ethylenedioxythiophene) thin films prepared by vapor phase polymerization

“…The absorbance maximum around 800 nm has been associated with polaron states in PEDOT [19], but also with several microscopic properties of polymer, e.g., defects and chain lengths [20]. The very broad absorption band at higher wavelengths in NIR area results from bipolaron states [19,20]. The increase of the absorbance at~900 nm combined with the decrease of the absorbance at higher NIR wavelengths displayed in Fig.…”

“…According to the experiments of Winther-Jensen and West, VPP PEDOT:Tos films have an absorption maximum above 1100 nm at pH 0e2, a maximum in the range of 850e950 nm at pH 4e10 and a maximum at 540e590 nm at pH 12e14. The absorbance maximum around 800 nm has been associated with polaron states in PEDOT [19], but also with several microscopic properties of polymer, e.g., defects and chain lengths [20]. The very broad absorption band at higher wavelengths in NIR area results from bipolaron states [19,20].…”

Decoupling order and conductivity in doped conducting polymers

“…Using the same samples as used for conductivity measurements, optical absorbance spectroscopy was performed for the stoichiometric EDOT:oxidant ratio at each stage of the manufacturing process. It can be seen in Figure 4 (for the VPP sample and in S4 for the cast sample) that peaks associated with polarons at ~ 825 nm and bipolarons at ~ 1200 nm 27,28 are observed in the disordered sample. However after ordering, the absorbance associated with both of these species significantly increases.…”