A New Method to Improve Poly(3-hexyl thiophene) (P3HT) Crystalline Behavior: Decreasing Chains Entanglement To Promote Order−Disorder Transformation in Solution

Abstract

We promoted order-disorder transformation of poly(3-hexylthiophene) (P3HT) in solution by ultrasonic oscillation which substantially improved crystallinity in its pure film. P3HT with low molecular weight (M(w)) dispersed very well in p-xylene solvent and few aggregates generated in the solution. For P3HT with high M(w), the results suggested the coexistence of two phases: disordered coils in solution and ordered microcrystals in suspension. Upon ultrasonic oscillating, more ordered precursors generated in solution due to increased self-assembly from disordered to ordered configuration, which resulting from decreased extent of chains entanglement existing in high molecular system, and red shift at absorption maximum and growing intensity of the pi-pi* absorption at ca. 604 nm were observed in solution. The films prepared from the oscillated solution then showed increased degree of crystallinity, pi-pi interactions and homogeneously distributed nanofibrils, which should be attributed to the ordered precursors constructed in solution. Furthermore, the best crystallinity of the film was obtained at the oscillating time of 4 min, showing the equilibrium state between the increased content of crystalline molecules and the shortened crystalline length. This simple method paves the way for the decreasing chains entanglement during crystallizing process of conjugated polymer in solution, and it enriches the ways to improve crystalline order in thin films comprising crystallizable polymers.

Structure and Morphology Control in Thin Films of Conjugated Polymers for an Improved Charge Transport

“…Thus, the importance of heating solutions before the next processing step [68,144,145] for the promotion of single coil chains is proved. Apart from thermal energy, ultrasonic vibration is also a effective method for disentanglement as reported by Zhao et al (Figure 18I) [146,147]. They reported that the P3HT chains with a larger molecular weight had a more severe entanglement due to the binary-hooking contact prevailing arising from the folding and distortion of conformation of high-M W polymer.…”

Carrier Transport Enhancement in Conjugated Polymers through Interfacial Self-Assembly of Solution-State Aggregates

“…[5][6][7][8][9][10] A number of recent studies have demonstrated that molecular ordering along the polymer backbone and between chains is far more important to carrier transport in high molecular weight (Mw) polymer films than domain boundaries. [11][12][13][14][15][16] However, high Mw semi-flexible polymers are thought to be difficult to push into a highly molecularly ordered state due to entanglements and interactions which can inhibit molecular diffusion and challenge conformational transitions. 11,13,17 Polymer crystallization improves the molecular stacking order and planarization of the backbone in the solid state, hence there have been a number of reports linking crystalline order to carrier transport.…”

“…11,13,17 Polymer crystallization improves the molecular stacking order and planarization of the backbone in the solid state, hence there have been a number of reports linking crystalline order to carrier transport. 7,18,19 Along this line, several strategies have been pursued to control molecular self-assembly and thin film microstructure, including by decreasing chain entanglements in the solution state, 12,13,17 tuning solution-processing conditions, [20][21][22][23][24] surface functionalization with a self-assembled monolayer (SAM) [25][26][27] and applying post-deposition thermal/solvent vapour annealing. [28][29][30] 3…”

“…Hence, disentanglement results in facile pre-aggregation of a large number of nuclei with uniform size distribution, leading -among other things -to a reduction of the specific viscosity of the solution and to easier diffusivity of pre-aggregates and chains. 12,31 During solution drying, disentangled chains and pre-aggregates therefore more easily assemble into structures exhibiting enhanced backbone planarity, lamellar thickness and extended π-π* conjugation. 32 Molecular self-assembly during solution-casting can be influenced by surface functionalization with a SAM, an effect widely recognized in solution-processed small-molecule organic semiconductors.…”

Coating on a Cold Substrate Largely Enhances Power Conversion Efficiency of the Bulk Heterojunction Solar Cell

“…[21][22][23][24][25][26][27][28] The rod conformation enhances the crystallization via the faceto-face assembly of the p-conjugation. [22,23] The increased conjugation length brings a red shift in UV-Visible absorption, [21][22][23][24] changing the color of the solution from orange to deep purple, as shown in the inset camera images. The P3HT solution was in a liquid nitrogen bath until the solution temperature was decreased to À40 8C and it was taken out in air.…”