Hole transport in polymeric field effect transistors and light-emitting diodes

The hole transport in the amorphous poly(2-methoxy-5-(3',7'-dimethyloctyloxy)-p-phenylene vinylene) (OC₁C₁₀-PPV) and in the more ordered poly[2,5-bis(3',7'-dimethyloctyloxy)-p-phenylene vinylene] (OC10C10-PPV) has been investigated both in field-effect transistors (FETs) and light-emitting diodes (LEDs) as function of temperature and applied voltage. From J-V measurements on LEDs a difference of 15x has been found in the hole mobility between OC₁C₁₀-PPV and OC₁₀C₁₀-PPV. In FETs the dependence of the field-effect mobility on the carrier density is much stronger in OC₁C₁₀-PPV than in OC₁₀C₁₀-PPV. These differences in the mobility in both FETs and LEDs are determined by the difference in microscopic transport parameters between the two materials, which results from a different ordering in the polymeric film of the PPV derivatives. Due to their specific chemical composition OC₁C₁₀-PPV is an amorphous polymer and the transport is the same in all directions, while OC₁₀C₁₀-PPV is more ordered and the transport shows anisotropy between sandwich and in-plane devices.