Unleashing the Potential of Raman Spectroscopy to Estimate PEDOT:PSS Doping Level and Crystalline Morphology

PSS is arguably the most popular conjugated polymer. However, its complex blend nature and low crystallinity make its characterization challenging. Raman spectroscopy is a fast and accessible technique for studying PEDOT:PSS. However, PEDOT:PSS Raman signals are convoluted, and their current interpretation, focused on the C_α═C_β peak (≈1435 cm^-1), cannot distinguish between doping and morphology information. The interpretation of PEDOT:PSS Raman spectra is advanced by expanding the research to other vibrational peaks. By comparing the Raman spectra of different PEDOT:PSS samples with GIWAX and XPS data, two equations are proposed to estimate the PEDOT π-π intermolecular spacing and doping levels from Raman data. The estimated PEDOT doping levels, which are confirmed with the corresponding equilibrium equation, allowed to calculate the PEDOT:PSS films' carrier mobility. Notably, the calculated mobilities agree with the transport coefficient fitted from the Kang-Snyder model. The high spatial resolution of Raman is exploited to realize a morphology and doping level 2D mapping on blank films that are locally treated by inkjet printing with 100 µm resolution. This study re-establishes the interpretation of PEDOT:PSS Raman spectra, demonstrates its potential for quantitative analysis of crystalline parameters, doping, and mobility, and opens the door to the local probing of those properties.