Towards low-voltage operated OTFTs via polymer semiconductor/dielectric blending

Achieving low-voltage operation in organic thin-film transistors (OTFTs) remains a primary challenge for wearable electronics. Here, low threshold voltage poly[2,5-(2-octyldodecyl)-3,6-diketopyrrolopyrrole-alt-5,5-(2,5-di(thien-2-yl)thieno [3,2-b]-thiophene)] (DPPDTT) OTFTs using ultrathin aluminium oxide (Al x O y ) as the gate dielectric are reported. Reducing the Al x O y thickness from 5 nm to 3 nm does not inherently improve the transistor performance. Modifying the 3 nm Al x O y with self-assembled monolayers (SAMs) usually used for alumina surface treatment increases field-effect mobility but does not appreciably enhance other important device parameters. To address this, a polymer semiconductor/dielectric blend consisting of DPPDTT (semiconductor) and poly(methylmethacrylate) (PMMA) (dielectric) has been applied. An optimized blend on 3 nm Al x O y yields DPPDTT OTFTs operating at the gate voltage | V G | ≤ 2 V with the field-effect mobility ( μ ) of ∼0.06 cm 2 ·V -1 ·s -1 , threshold voltage | V T | below 1 V, subthreshold swing ( SS ) around 100 mV/dec, and on/off current ratio ( I on /I off ) in excess of 5 × 10 4 . These results demonstrate that polymer blending may provide a more robust interface passivation than application of SAMs, which is particularly important for OTFTs using ultrathin metal oxide dielectrics.