Oriented growth of lamellar crystals of semiconductive conjugated polymers
After annealing, (100) and (200) diffraction arcs of PBTTT-C14 lamellar crystals appear on the meridian of 2D X-ray diffraction patterns. Thus the edge-on packing of conjugated backbones of PBTTT-C14 within lamellar crystals is manifested.
(A) TEM image of ordered lamellae stacking of PBTTT-C14. The b axis and c axis of PBTTT-C14 lamellar crystals are identified via the diffraction arcs shown on the corresponding diffraction pattern. (B) The schematic illustration of the regular edge-on organization of conjugated PBTTT-C14 backbones with black stripes.
Effects of phase separation of constituent components and oriented arrays of semiconducting lamellar crystals on devices performances
(a) Schematic illustration of the prepared organic TFT device, and within the active layers, the oriented arrays of lamellar crystals composed of edge-on organization of semiconductive P3HT segments have been developed. (b) Typical transfer curves (drain current, ID, as a function of gate bias, VG, at a drain-to-source bias, VDS) of P3HT-based TFTs using various blending active layers have been illustrated as the function of weight percent of amorphous PMMA component in the films. (c) Comparison of output curves (ID as a function of VDS at various VG) of P3HT-based TFTs with (lines) and without (circles) blending with 75% PMMA as the active layer. (d) Comparison of normalized ID as a function of time at selected operational conditions. ID0 and IDT are the drain current at the initial and at a given time, respectively. The corresponding gate current (IG) of the 25:75 P3HT/PMMA devices is also shown. According to this result, the measured current between source and drain is successfully independent, and for this current of concern, the decay with time is generally considered unavoidable for organic devices.
Schematic diagram of the blending film with multiscale phase-separated morphology. During turn-on of PTFTs, the molecular dipole of the PMMA nanodomain can be aligned with the use of applied external gate voltage (VG) to aid in charge accumulation at a relatively small given voltage. The diagram also shows that unintentional impurities can be absorbed by the PMMA domains. The calculated dipole moment (μ) based on a monomer of PMMA is also shown by density functional theory (DFT) with B3LYP/6-31G method, and the vector indicates the direction of the dipole moment.
Schematic drawing of the microstructures within active layers of (a) spin-coated P3HT OTFT and H-P3HT OTFT with stripe morphology (b) parallel and (c) perpendicular to the Ag electrodes. The green dotted lines indicate the paths of hole transport. With the pi-pi stacking of conjugated P3HT backbones parallel to the electrodes, electron transfer via the hopping mechanism through stacked backbones is able to reach electrodes more efficiently, and therefore much better charge mobility is measured.