The effect of nitric acid (HNO3) treatment on the electrical conductivity and stability of poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) thin films

In this work, the posttreatment of an organic polymer is performed using an inorganic acid, nitric acid (HNO3). We picked poly(3,4-ethylenedioxythiophene): poly( styrenesulfonate) (PEDOT: PSS) as the base material and improved its electrical conductivity by acid treatment with different concentrations of HNO3. The acid treatment was able to achieve the optimum electrical conductivity of 197 S/cm, which is 115.5 times higher than the base material when treated with an aqueous solution containing 65% of HNO3. Moreover, the films showed higher transparency in the visible range while conducting Fourier transform infrared analysis. In addition, the treated films showed improved stability against outdoor operating conditions in terms of sheet resistance compared with untreated PEDOT: PSS films. We tried to develop a hypothesis to describe the reason behind the electrical conductivity enhancement by studying the thicknesses of all the samples at different acid concentration levels. The results from atomic force microscopy, the Hall effect, and the trend of film thickness suggest that the conformational change, the removal of excess PSS from the polymer, and the increase in carrier concentration are the reasons behind the improvement in electrical conductivity.