Charge transport studies in fluorene – Dithieno[3,2-b:2′,3′-d]pyrrole oligomer using time-of-flight photoconductivity method

Charge mobility characteristics of a newly synthesised 2,6-bis[2-(9,9-dihexyl-9H-fluorene)]-N-(4-hexylphenyl)-dithieno[3,2-b:2′,3′-d]pyrrole oligomer (DTP-FLU) was studied as a function of electric field and temperature using time-of-flight photoconductivity measurement. It is found that the DTP-FLU oligomer is a hole transporting material with a hole mobility of 7.7 × 10−6 cm2/Vs at an applied electric field of 2.9 × 105 V/cm at 298 K. The dependence of hole mobility with applied electric field and temperature is studied in detail by analyzing the experimental results using the Bassler’s Gaussian disorder model and Correlated disorder model. The energetic disorder parameter (σ) = 100 meV, mobility pre-factor (μ∞) = 6.1 × 10−4 cm2/Vs and positional disorder parameter (Σ) = 2.4 were extracted using Gaussian disorder model. The film morphology and photophysical properties of this new oligomer are also studied in detail.