In-situ characterization of electrochromism based on ITO/PEDOT：PSS towards preparation of high performance device

Poly（3,4-ethylenedioxythiophene）：poly（styrenesulfonate）（PEDOT：PSS） is usually sandwiched between indium tin oxide（ITO） and a functional polymer in order to improve the performance of the device. However, because of the strong acidic nature of PEDOT：PSS, the instability of the ITO/PEDOT：PSS interface is also observed. The mechanism of degradation of the device remains is unclear and needs to be further studied. In this article, we investigate the in-situ electrochromism of PEDOT：PSS to disclose the cause of the degradation. X-ray photoelectron spectroscopy（XPS） was used to characterize the PEDOT：PSS films, as well as the PEDOT：PSS plus polyethylene glycol（PEG） films with and without indium ions. The electrochromic devices（ECD） based on PEDOT：PSS and PEG with and without indium ions are carried out by in-situ micro-Raman and laser reflective measurement（LRM）. For comparison, ECD based on PEDOT：PSS and PEG films with LiCl, KCl, NaCl or InCl_3 are also investigated by LRM. The results show that PEDOT：PSS is further reduced when negatively biased, and oxidized when positively biased. This could identify that PEDOT：PSS with indium ions from PEDOT：PSS etching ITO will lose dopants when negatively biased. The LRM shows that the device with indium ions has a stronger effect on the reduction property of PEDOT：PSS-PEG film than the device without indium ions. The contrast of the former device is 44%, that of the latter device is about 3%. The LRM also shows that the contrasts of the device based on PEDOT：PSS＋PEG with LiCl, KCl, NaCl, InCl_3 are 30%, 27%, 15%, and 18%, respectively.