Conductivity relaxation and photocurrent generation in reduced graphene oxide-poly(9,9′-dioctyl-fluorene-co-bithiophene) composite with application in temperature sensing

Abstract

The electrical transport properties and photocurrent generation in a reduced graphene oxide-poly(9,9′-dioctyl-fluorene-co-bithiophene) (RGO-F8T2) composite were investigated. The semiconducting nature of the RGO-F8T2 composite was jointly demonstrated by dc and ac conductivity measurements. The dc conductivity obtained from both dc and ac measurements follows the Arrhenius relationship with the activation energy of the order of 80 meV. The RGO-F8T2 composite also showed excellent temperature sensing properties. The temperature coefficient of resistance was compared to commercially available Platinum, Polysilicon, and Germanium temperature sensor. The conductivity relaxation mechanism in the RGO-F8T2 composite depicted the mechanism behind ac conduction. This was due to phonon assisted tunneling between the defect states. The density of states at the Fermi level increases by one order of magnitude for the temperature change of 301 to 433 K. The scaling of conductivity isotherms established the occurrence of intramolecular energy transfer from disordered to ordered chain segments or both in the composite. The photocurrent generation in the RGO-F8T2 composite thin film under simulated solar light illumination was also studied. Here, a linear variation of the photosensitivity with the variation of the incident light intensity was observed.