Increase in hole mobility in poly (3-hexylthiophene-2,5-diyl) films annealed under electric field during the solvent drying step

Abstract Higher electrical charge carrier mobility in polymer semiconductor films is important to build electronic and opto-electronic devices with improved performance. Application of electric field of the order of 2000 V cm − 1 during the solvent drying step for the formation of poly (3-hexyl thiophene-2,5-diyl) (P3HT) film is shown to significantly increase the hole carrier mobility. The reasons for increase in mobility by this novel technique are investigated in this paper. The X-ray diffraction measurements confirm the increase in crystallinity of the films for electric-field annealed samples, while the analysis of the data shows increase in the size of the ‘crystallites’ in those films. The current density–voltage data corresponding to the space charge limited currents at various low temperatures for hole-only devices with P3HT film when fitted to the empirical model for electric-field annealed samples, show an increase in zero field mobility ( μ 0 ) and correspondingly a decrease in activation energy ( E a ) and the field dependence pre-factor ( γ ). The data fitted to the Gaussian disorder model also shows a decrease in the energetic disorder ( σ ) in the polymer films due to electric-field annealing – indicative of increased ordering of molecules in those films. The analysis confirms the improvement of ordering of the polymer in the film formed due to application of electric field during the solvent drying step of the film formation – a simple processing technique which may be implemented to fabricate higher mobility polymer films for building improved organic electronic devices.