Enhanced Microstructural Uniformity in Sulfuric-Acid-Treated Poly(3,4-Ethylenedioxythiophene):Poly(Styrene Sulfonate) Films Using Raman Map Analysis

Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films have emerged as potential alternatives to indium–tin oxide as transparent electrodes in optoelectronic devices because of their superior transparency, flexibility, and chemical doping stability. However, pristine PEDOT:PSS films show low conductivities because the insulating PSS-rich domains isolate the conductive PEDOT-rich domains. In this study, the conductivities and corresponding spatially resolved Raman properties of PEDOT:PSS thin films treated with various concentrations of H₂SO₄ are presented. After the PEDOT:PSS films are treated with the H₂SO₄ solutions, their electrical conductivities are significantly improved from 0.5 (nontreated) to 4358 S cm⁻¹ (100% v/v). Raman heat maps of the peak shifts and widths of the C_α═C_β stretching mode are constructed. A blueshift and width decrease of the C_α═C_β Raman mode in PEDOT are uniformly observed in the entire measurement area (20 × 20 µm²), indicating that microstructural transitions are successfully accomplished across the area from the coiled to linear conformation and high crystallinity upon H₂SO₄ treatment. Thus, it is proved that comprehensive Raman map analysis can be easily utilized to clarify microstructural properties distributed in large areas induced by various dopants. These results also offer valuable insights for evaluating and optimizing the performance of other conductive thin films.