Evaluation of a reliable electrochromic device based on PEDOT:PSS-TiO2 heterostructure fabricated at low temperature

Abstract

A poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS)-TiO2 composite layer was fabricated using a nanoparticle deposition system (NPDS) followed by spin coating process. The charge balance and transmittance change of electrochromic (EC) devices were investigated with different electrolytes, such as LiClO4-based polymer electrolyte and ionic liquid (IL). It was found that the EC properties could be improved using 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM-TFSI) with high ionic conductivity, and a symmetric charge balance change can be obtained showing rapid switching. The PEDOT:PSS-TiO2 composite exhibited stable performance without degradation after 500 cycles, maintaining the same cyclic voltammetry (CV) curve. It seems that heterostructure of TiO2 with PEDOT:PSS showed good separation of electrons and holes, making TiO2 an efficient electron transport material with PEDOT:PSS being an efficient hole transport material. Thus, it was found that the organic-inorganic structure obtained by our simple and novel process was effective in improving EC properties due to efficient separation of electrons and holes.