Using vapor phase polymerization (VPP) method, PEDOT can deposite easily onto a variety of flexible or nanopatterned substrate. And some research results show that VPP PEDOT also demonstrates unique and promising thermoelectric properties. Compared to PEDOT:PSS, which has a PSS to PEDOT weight ratio of 2:1, VPP method has significantly lower concentration of tosylate in the polymer matrix. The PSS in PEDOT:PSS often results in the interfacial instability of organic electronic devices, the VPP process offers an attractive route to build highly stable PEDOT electrodes.

Recently, OuYang et al. (DOI:10.1039/C7TC04661H.) reported the synthesis of PEDOT through VPP method using PEG-PPG-PEG as substrate. Firstly, 40% iron (III) p-toluenesulfonate butanol solution was diluted with butanol. The dilution was then mixed with PEG-PPG-PEG. And the final solution contained 21% iron (III) tosylate and 20% triblock copolymer. The oxidizer solution was then spin coated onto the precleaned substrates. The coated substrates were quickly dried at 70 °C for 1 min and then dried at 45 °C for 2 mins. They were then transferred into a 35 °C vaccum oven. After 30 seconds of equilibration, EDOT was placed into the oven. The substrates and the monomer container were covered with a 4 L polystyrene lid with an air outlet to reduce the total volume of vapour chamber. The whole system was then pumped for 1 minute until the vacuum gauge read -760 mmHg. The pump was then turned off and the vacuum was maintained for desired lengths of time. After the polymerization, the oven was vented and the samples were immediately taken out and washed 5 to 10 times with ethanol.

Although the above method is easily operated, the PEDOT film will contract after washing to remove excessive polymer:oxidizer trapped in PEDOT matrix. And the research of OuYang et al. shows that the PEDOT chain adopts a neutral benzenoid conformation in its unwashed condition; the polymer chain converts into the charged quinoid structure after the removal of oxidizers with solvent washing. Meanwhile, dopants are incorporated between the polymer chains, forming a more compact and ordered structure. A solution to the above problem is to depend on mechanical clamping of the film edges to suppress contraction.

In a word, synthesis of PEDOT using VPP method is easy. But PEDOT structural rearrangement is occurred during rinsing that will have an effect on its conductivity and transparency. So understanding the mechanism of the PEDOT structural transformation is helpful for designing methods for optimizing the morphology and doping of VPP PEDOT as high performance organic electrode materials.

Edited by Suzhou Yacoo Science Co., Ltd.