Comparison of organic thermistors based on PEDOT:PSS and PEDOT:tos thin films under various thermal and humidity conditions

• Published in: Sensors and actuators. B, Chemical Vol. 275; pp. 359 - 366
• Main Authors: Štulík, J., Polanský, R., Hamáček, A., Nešpůrek, S., Slepička, P., Kolská, Z., Švorčík, V.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 01.12.2018; Elsevier Science Ltd
• Subjects: Atomic force microscopy; Construction costs; Contact angle; Electrokinetics; Electronics; Flexible electronics; Humidity; Organic chemistry; Organic thermistor; PEDOT:PSS; PEDOT:tosylate; Photoelectrons; Printed thermistor; Sulfonic acid; Sulfur trioxide; Surface properties; Thermistors; Thin films; Wettability; X ray photoelectron spectroscopy; X ray spectra; Flexible electronics; Organic thermistor; Printed thermistor; Humidity; PEDOT:PSS; PEDOT:tosylate
• ISSN: 0925-4005; 1873-3077
• DOI: 10.1016/j.snb.2018.08.054

•Flexible thermistors based on PEDOT:PSS and PEDOT:tos were studied in detail.•Their usage in low-cost production of printed temperature sensors is considered.•The absence of sulfonic acid decreases the hydrophilicity of the PEDOT:tos structure.•PEDOT:tos thermistor has better humidity stability and a higher change in resistance. Flexible organic thermistors based on poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) [PEDOT:PSS] and PEDOT:Fe3+(O−tosylate)3 [PEDOT:tos, tosylate ≡ p-toluenesulfonate] thin films were prepared and their structural and surface properties and the humidity and temperature dependences of their resistance were studied. The surface wettability evaluated by goniometry revealed a considerably higher contact angle (70°) on the PEDOT:tos thin film surface, indicating its hydrophobic nature. In contrast, a large number of polar SO3 groups are present on the surface of the PEDOT:PSS thin film, proving its overall wettability. The results obtained from atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) together with electrokinetic analysis indicate expressly different surface charges (and chemistry) for the two films tested. The absence of sulfonic acid in the PEDOT:tos thermistor markedly enhances its humidity stability in the range of 20–90% RH, as confirmed during the humidity and temperature tests. Moreover, exposure of both thermistors to step-wise change in temperature showed that the PEDOT:tos thermistor features a notably higher change in resistance ΔR/R0 than the PEDOT:PSS thermistor. These observations suggest that structures based on PEDOT:Fe3+(O−tosylate)3 are promising candidates for the low-cost construction of flexible printed organic thermistors.