Fluorinated alkyl phosphonic acid SAMs replace PEDOT:PSS in polymer semiconductor devices

Fluorinated phosphonic acids were self-assembled to form monolayers (SAMs) on indium tin oxide anodes, resulting in work functions that are 0.15–0.4 eV larger than PEDOT:PSS by Kelvin probe. X-ray photoelectron spectroscopy and water contact angle measurements were used to study monolayer growth kinetics and to verify the degree of coverage. Hole-only devices and white polymer light emitting diodes were constructed using unmodified ITO, SAM-modified ITO, and PEDOT:PSS on ITO to investigate the influence of the fluorinated SAMs on hole injection. Hole-only devices indicate improved hole injection compared to PEDOT:PSS. Compared with light-emitting diodes using pure ITO anodes, the SAM-modified devices show improved charge injection and ten times higher luminous efficiency. Compared to devices using PEDOT:PSS, SAM-modified devices show improved brightness and luminous efficiency, although with a slightly larger turn-on voltage. These materials are therefore suitable candidates to replace PEDOT:PSS as a hole injection layer in PLEDs.

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► PEDOT:PSS-free semiconductor devices.
► ITO work function modification using fluorinated self-assembled monolayers.
► Device studies correlated with Kelvin probe work function measurements.
► SAM growth and coverage studied by XPS.