Controlling charge injection properties in polymer field-effect transistors by incorporation of solution processed molybdenum trioxide

Abstract

A simply and facilely synthesized MoO3 solution was developed to fabricate charge injection layers for improving the charge-injection properties in p-type organic field-effect transistors (OFETs). By dissolving MoO3 powder in ammonium (NH3) solvent under an air atmosphere, an intermediate ammonium molybdate ((NH4)2MoO4) precursor is made stable, transparent and spin-coated to form the MoO3 interfacial layers, the thickness and morphology of which can be well-controlled. When the MoO3 layer was applied to OFETs with a cost-effective molybdenum (Mo) electrode, the field-effect mobility (μFET) was significantly improved to 0.17 or 1.85 cm(2) V(-1)s(-1) for polymer semiconductors, regioregular poly(3-hexylthiophene) (P3HT) or 3,6-bis-(5bromo-thiophen-2-yl)-N,N'-bis(2-octyl-1-dodecyl)-1,4-dioxo-pyrrolo[3,4-c]pyrrole (DPPT-TT), respectively. Device analysis indicates that the MoO3-deposited Mo contact exhibits a contact resistance RC of 1.2 MΩ cm comparable to that in a device with the noble Au electrode. Kelvin-probe measurements show that the work function of the Mo electrode did not exhibit a dependence on the thickness of MoO3 film. Instead, ultraviolet photoemission spectroscopy results show that a doping effect is probably induced by casting the MoO3 layer on the P3HT semiconductor, which leads to the improved hole injection.

Interface Doping for Ohmic Organic Semiconductor Contacts Using Self‐Aligned Polyelectrolyte Counterion Monolayer

“…Furthermore, the R c characteristics evolve from dispersive behavior on Au to nondispersive behavior on h 2 , that is, R c becomes independent of I sd and σ; a signature of the true ohmic contact (Figure d). The R c values attained here are superior to those using solution‐processed MoO 3 (120 kΩ cm) with a related DPP polymer in the same OFET configuration . Taking into account the space‐charge resistance of the intervening semiconductor layer, we evaluated ρ c to be 1, 4, and 9 Ω cm 2 for h 2 , h 1 , and bare Au, respectively (Note S5, Supporting Information).…”

Universal diffusion-limited injection and the hook effect in organic thin-film transistors

“…The bottom contact electrodes were fabricated by sputtering Ni/Mo (3/13 nm) and conventional photolithography process to define patterns for source and drain electrodes. For the MoO 3 interlayers, the ammonium molybdate (NH 4 ) 2 MoO 4 in H 2 O solution (0.8 wt% of MoO 3 ) was spin-coated and annealed at 150 °C for 10 min in air 30 . For V 2 O 5 interlayers, the ammonium vanadate ((NH 4 ) 3 VO 4 ) solution of different concentration (0.1–0.5 wt% of V 2 O 5 ) was spin-coated and then annealed at 150 °C for 20 min in air 23 .…”

Understanding of copolymers containing pyridine and selenophene simultaneously and their polarity conversion in transistors

“…Furthermore, we attempted to modify the Au source/drain electrodes by doping NaHCO 3 , in order to look into the possibility of an n-type unipolar device, which is essential for a p-n junction with a complementary device due to the defects of ambipolar devices derived from the opposing charge flows. [66][67][68][69] For increasing the positive voltage, the hole transport in the ambipolar devices increased the off current and operated as a leakage current in electron transport. For increasing the negative voltage, the electrons acted as a barrier to the hole transport, consequently reducing the on/off characteristics of the devices and the accuracy in extracting the mobility and threshold voltage.…”