Thin Films Of Regioregular Poly Research Articles

Delocalized polarons in self-assembled poly(3-hexyl thiophene) nanocrystals

We have studied the characteristic properties of charged excitations (polarons) in thin films of regioregular poly(3-hexylthiophene) (RRPHT) by optical spectroscopies. We found that the increased interchain coupling that exists in self-assembled lamellae in these films drastically changes the properties of the polaron excitations. The traditional self-localized polaron in one-dimension delocalizes in two-dimensions, resulting in a much-reduced relaxation energy and multiple absorption bands, the most dominant being in the mid-infrared (IR) spectral range. Also it has associated IR and Raman active vibrations with reverse absorption bands [anti-resonances (AR)] compared with the continuum electronic band. The AR are attributed to the electron–phonon interaction.

Time-of-flight measurements in thin films of regioregular poly(3-hexyl thiophene)

We have studied the transport of holes in thin films of regioregular poly(3-hexyl thiophene) (RRPHT). In comparison to regiorandom poly(3-hexyl thiophene) (PHT), RRPHT is a promising material for electronic devices, due to the high field effect mobility observed. We have studied the photogenerated charge carrier transport by using the integral time-of-flight (TOF) method. We have also studied the transport properties of the equilibrium charge carriers by a newly developed method of equilibrium charge carrier extraction in the case of a linearly increasing voltage. From TOF measurements in the subnanosecond time scale, it was experimentally obtained that the drift distance of holes is smaller than the inter-electrode distance in both PHT and RRPHT films and the mobility is higher than 10−2 cm2/Vs. In the millisecond time scale we obtained additional low mobility of equilibrium holes in RRPHT.

Ultra-low-threshold field emission from conjugated polymers

Field-emission displays contain materials that emit electrons when charged to a low (negative) potential; the electrons excite light emission from phosphor screens. These devices have the potential to provide flat-panel visual displays with good picture quality at low power consumption and low cost1. Field-emission devices at present use arrays of microfabricated tips as the emitting cathodes, but a potentially cheaper and simpler alternative is to use a thin-film cathode. This requires the identification of materials that will emit an appreciable electron current at low applied fields. Nitrogen-doped, chemical-vapour-deposited diamond films2 and amorphous carbon films3 have been explored for this purpose. The low electron affinity4, wide bandgap and excellent transport properties5 of some conducting organic polymers suggest that they might also provide good cathode materials. Here we demonstrate that this is so, reporting field emission from thin films of regioregular poly(3-octylthiophene) deposited on n-doped silicon, with indium tin oxide as the anode. The threshold fields that we measure for electron emission from these films are the lowest yet reported for any carbon-based material.

Determination of the optical constants of thin films of regioregular poly(3-alkylthiophene) on transparent substrates

The methods of reflection and transmission are used to determine the optical constants n and k of thin films of regioregular poly (3-octylthiophene). The technique is based on the simultaneous use of Fresnel laws and the dispersion relations between n and k of the film using an iterative process. The optical and Tauc gaps are also derived.