Secondary electrochemical doping level effects on polaron and bipolaron bands evolution and interband transition energy from absorbance spectra of PEDOT: PSS thin films

• Electrochemical doping of PEDOT:PSS films introduces mid-gap absorption states.
• Optical spectra confirms charge storage in the form of polaron/bipolaron bands.
• Lower energy IR peak remains nearly constant while higher energy peak shows a red shift with doping.
• Energy level diagram has been sketched from optical absorption data at different doping levels.
• Colorimetric curve plotted on chromaticity diagram shows a non-linear characteristic on doping.

Doping induced effect on interband transition energy levels of PEDOT: PSS films deposited by spin coating have been studied experimentally by following changes in vibrational, optical and electrochemical properties. Absorbance spectra of films have been used as a tool to study formation of polaron/bipolaron bands, their energy shift and binding energies with change in doping concentration. Energy level structure evolving from optical spectra has been sketched and corresponding energies required for transition at different doping levels have been indicated. Electrochemical studies show redox peaks in agreement with spectroscopic results demonstrating storage of charge in sub-band states in the form of polarons/bipolarons. Increased absorbtion due to π-π* transitions on secondary doping reveal non linear characteristic in the plot of hue vs.chroma traversing from faint blue to deep blue region in the chromaticity diagram.

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