Effect of Solvent Evaporation Rate on Order-to-Disorder Phase Transition Behavior of Regioregular Poly(3-butylthiophene)

Abstract

The effect of solvent evaporation rate on the crystal modification and the thermal stability of solution cast regioregular poly(3-butylthiophene) (P3BT) film was investigated by WAXD, DSC, and FTIR. It is found that, independent of the solvent evaporation rates, the P3BT films prepared from chloroform solution demonstrate essentially the same interlayer distance, which is very close to the reported value of form I′, rather than the conventional form I. However, in the DSC heating curves, it is interesting to find that a single “melting” peak and a double one in the temperature region of 45–100 °C can be observed respectively for P3BT films prepared with fast and extremely slow solvent evaporation rates. The double melting behavior of P3BT in this low-temperature region has never been discussed in the literature. By temperature-dependent infrared spectroscopy, it is shown that these low-temperature “melting” peaks are related to the order-to-disorder phase transition (form I′ to form I) of P3BT. Furthermore, our spectral studies reveal that the “melting” peak around 58 °C in the DSC heating trace is associated with the conformational disordering of butyl side chains, whereas the destruction of backbone planarity and the disordering of π–π stacking can take place at higher temperature (ca. 82 °C) with decreasing the solvent evaporation rate.

Impact of side‐chain length on the phase structures of P3ATs and P3AT:PCBM films as revealed by SSNMR and FTIR

“…Poly(3‐alkylthiophenes) (P3ATs) as the representative of conductive polymers have drawn enormous interests due to their potential application in the organic field‐effect transistors (OFETs) and organic photovoltaic devices such as polymer solar cells (PSCs) . As the semicrystalline polymers, the device properties of each P3AT member strongly depend on their crystalline structures and morphologies in prepared films, which can be controlled via varying regioregularity, molecular weight, or thermal/solvent treatment . To the whole family, in order to balance the processing and device properties, the side‐chain length should be considered when choosing P3ATs as the active layer .…”

“…4,5 As the semicrystalline polymers, the device properties of each P3AT member strongly depend on their crystalline structures and morphologies in prepared films, [6][7][8] which can be controlled via varying regioregularity, 1 molecular weight, 9 or thermal/ solvent treatment. [10][11][12] To the whole family, in order to balance the processing and device properties, the side-chain length should be considered when choosing P3ATs as the active layer. [13][14][15][16] Therefore, much effort has been put on the side-chain organization and its effect on the main-chain structures.…”

Control over the photophysical properties of nanoparticles of regioregular poly(3-octylthiophene) using various poor solvents

“…The relatively small interlayer spacing in Form II indicates the interdigitation of alkyl side chains. Recently, another crystal structure named Form I 0 has been reported [51][52][53]. This new crystal structure is closely related to that of the common Form I.…”

Rotation‐assisted formation of poly(3‐butylthiophene) nanowires: Morphology, microstructure, and electrical property

“…It has been well accepted that P3BT molecular chains could organize into polymorphic crystal modifications, with characteristic of distinguished interlayer distance ( d 100 ). P3BT form I and I′ crystals have close d 100 of 13.1 and 12.5 Å, respectively, whereas form II shows the decreased d 100 of 9.6 Å attributed from the interdigitated side‐chain packing . Figure (a) shows the WAXD profile of the sample prepared from 0.04 wt % P3BT/anisole solution with rotation, in which the (100) reflection locates at 2 θ = 6.9 °, leading to the d 100 spacing of 12.6 Å.…”