Piezoresistance of Poly(3-Hexylthiophene) Film

The piezoresistive devices with the structure of ITO/poly(3-hexylthiophene) (P3HT; spin coating 90 nm film)/Al (75 nm) have been fabricated and measured. We measured the I-V characteristics of the devices under different stresses. The stress ranges from 0 to 510 kPa and the voltage ranges from 0 to 5 V. The resistance of the devices is very sensitive to the applied stress. The piezoresistive coefficient is far larger than 10−4/Pa when the working voltage ranges from 0.2 to 0.5 V and the stress ranges from 160 to 510 kPa, whereas the current seems to change linearly with pressure and with a considerable fluctuation. This uncertainty in piezoresistance measurement may have originated from the viscoelasticity of P3HT, including a significant creep and a slow restoration after a deep compression, which has been confirmed by the results of the nanoindentation test. In general, P3HT could be used in tactile sensors, which need more sensitivity rather than accuracy.