Investigation of the mechanism of a facile method for ammonia treatment to effectively tune the morphology and conductivity of PEDOT:PSS films

Although there are some advantages of PEDOT:PSS films, including high conductivity, high transparency to visible light, excellent water solubility, and being environmentally-friendly, PEDOT:PSS solutions are acidic owing to the PSS polymer with a –SO₃H group donating the hydrogen ions. This results in the etching of the ITO surface as the PEDOT:PSS films are deposited on the ITO substrates using a spin coating process, which is attributed to the migration of indium and tin into the PEDOT:PSS film. In this paper, a PEDOT:PSS solution was treated with ammonia with different volume ratios prior to deposition. It is found that ammonia treatments can totally neutralize the hydrogen ions and reduce the A_In³⁺/A_{In³⁺(pristine)} atomic area ratio of PEDOT:PSS surface calculated from the XPS data due to the inhibition of the degradation at the PEDOT:PSS/ITO layer interface. Furthermore, the A_SO3H/A_SO3⁻ on the PEDOT:PSS surface obviously changes with ammonia-treated solution at pH < 7, and A_PEDOT/A_PSS is greatly influenced by an ammonia-treated solution at pH > 7, which affects the surface energy of PEDOT:PSS film, helps improve the film roughness, and enhances the electrical conductivity of the films.