Air-stability and bending properties of flexible organic field-effect transistors based on poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)]

• Flexible all-polymer field effect transistors are fabricated using PCDTBT as an active channel.
• FETs show an average on–off ratio of ∼105, which is independent of the channel length.
• The devices are air stable for 70 days (temperature: 20–35 °C and relative humidity: 70–85%).
• No change in mobility up to a compressive/tensile strain of 1.2%.

We have fabricated flexible field-effect transistors (FETs) using poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)], PCDTBT, as an active channel, poly(methyl methacrylate) (PMMA) as gate dielectric and biaxially oriented polyethyleneterephthalate (BOPET) as supporting substrate. The output and transfer characteristics of the devices were measured as a function of channel length. It has been observed that various OFET parameters viz. on–off ratio (∼105), mobility (μ ∼ 10−4 cm2 V−1 s−1), threshold voltage (Vth ∼ −14 V), switch-on voltage (Vso ∼ −6 V), subthreshold slope (S ∼ 7 V/decade) and trap density (Nit ∼ 1014 cm−2 V−1) are almost independent of the channel length, which suggested a very high uniformity of the PCDTBT active layer. These devices were highly stable under atmospheric conditions (temperature: 20–35 °C and relative humidity: 70–85%), as no change in mobility was observed on a continuous exposure for 70 days. The studies on the effect of strain on mobility revealed that devices are stable up to a compressive or tensile strain of 1.2%. These results indicate that PCDTBT is a very promising active layer for the air stable and flexible FETs.

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