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

Abstract

PEDOT: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 Cα═Cβ 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.