Natural polyelectrolyte: Major ampullate spider silk for electrolyte organic field-effect transistors

• A new application of major ampullate spider silk to OFETs is presented.
• Water molecules in the MA silk thin film improve the performance of OFETs.
• The model of EDLC may explain the device performance in air ambient.

The major ampullate (MA) silk collected from giant wood spiders Nephila pilipes consists of 12% glutamic acid (Glu) and 4% tyrosine (Tyr) acidic amino residues. The MA silk may act as a natural polyelectrolyte for organic field-effect transistors (OFETs). Pentacene and F16CuPc OFETs were fabricated with the MA silk thin film as the gate dielectric. The MA silk thin film with surface roughness of 4 nm and surface energy of 36.1 mJ/m2 was formed on glass using a hexafluoroisopropanol (HFIP) organic process. The MA silk gate dielectric in pentacene OFETs may improve the field-effect mobility (μFE,sat) value in the saturation regime from 0.11 in vacuum to 4.3 cm2 V−1 s−1 in air ambient at ca. 70% RH. The corresponding threshold voltage (VTH) value reduced from −6 V in vacuum to −0.5 V in air ambient. Similar to other polyelectrolytes, the changes of μFE,sat and VTH may be explained by the generation of electric double layers (EDLs) in the MA silk thin film in air ambient due to water absorption.

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