Multi-functional organic field effect transistor based on a dual doped P3HT

Abstract

A dual doped regio-regular poly(3-hexylthiophene-2, 5-diyl) (P3HT) was investigated to develop a multi-functional organic field effect transistor (OFET). OFETs based on a pristine P3HT and a dual doped P3HT (P3HT:PCBM:I2 blend) were fabricated to study the impact of doping on the electrical properties of the samples, and to examine the mechanism through which it amplified the output performance of the doped OFETs. A series of experimental techniques such as device electrical characterization, active layer surface analysis, and photon absorptivity measurements were conducted to quantitatively characterize the principal parameters that are susceptible to change as a result of doping. Topographic mapping revealed the expected doping-induced improvements in surface morphology, which could be associated with the ability of iodine to improve interdigitation between adjacent P3HT chains. Similarly, absorption spectra showed a 3 nm red-shift of the light absorbance spectrum of the doped samples compared to the undoped samples. The electrical conductivity of the samples was also examined at various conditions of temperature and light intensity, and the values obtained from the doped sample were approximately one order of magnitude higher compared to those of the undoped sample at room temperature, which explains the reason behind the higher output current drawn from the doped device compared to that of the undoped OFET. The explanation for this is two-fold, both PCBM and iodine promote the generation of free charge carriers, which increases the electrical conductivity of the active layer; and in addition to that, the improved P3HT main-chain interdigitation brought about by the introduction of iodine results in an increase in charge-carrier mobility, which also results in higher electrical conductivity. The findings of this study offers valuable information that could be instrumental in further advancing the future organic semiconductors based studies.

Keywords

• semiconducting polymers
• doping
• charge generation
• charger mobility
• thin-film morphology
• organic field effect transistors (ofets)
• multi-functionality