Morphological influence of polypyrrole nanoparticles on the performance of dye-sensitized solar cells

Polypyrrole (PPy) with various morphologies were synthesized by chemical oxidative polymerization and further used as the counter electrode (CE) in dye-sensitized solar cells (DSSCs). The conventional anionic surfactant, docusate sodium salt (AOT), cationic surfactant, cetylmethyl ammonium bromide (CTAB), and the newly developed polymeric dispersant, poly(oxyethylene)-imide (POEM), were employed in the PPy synthesis. Scanning electron microscopy images (SEM) revealed diversified morphologies of the synthesized PPy nanoparticles with irregular sheet (IS), hierarchical nanosphere (HNS), and nanosphere (NS), corresponded to the choice of the commercial surfactants AOT and CTAB, as well as the home-made POEM, respectively. Fourier transform spectroscopy (FT-IR) and X-ray diffraction (XRD) analysis were used to confirm the PPy structures and crystalline properties. When fabricated into films and used as CE in DSSCs, the PPy-HNS demonstrated the superior cell efficiency of 6.71±0.16% to those of PPy-IS (5.46±0.31) and PPy-NS (6.31±0.24), respectively. The excellent electrocatalytic ability of PPy-HNS was essentially attributed to its high electrochemical surface area (A_e), which was quantitatively calculated through a rotating disk electrode system by using the Koutecky-Levich equation. Brunauer-Emmett-Teller (BET) surface area measurement, electrochemical impedance spectroscopy (EIS), and cyclic voltammetry (CV) were also used to substantiate the explanation for the DSSC performances.