Control of Nucleation Density in Conjugated Polymers via Seed Nucleation

Abstract

The development of processing methods to precisely control the solution state properties of semiconducting polymers in situ have remained elusive. Herein, a facile solution seed nucleation processing method is presented in which nucleated poly­(3-hexylthiophene) (P3HT) solutions are blended with well-solvated, non-nucleated counterparts as a means to promote the formation of interconnected polymer networks. Nucleation and growth of these networks was induced by preprocessing the solution with UV irradiation and subsequent solution aging prior to deposition via blade-coating. This process was adopted for both batch and continuous flow processing. Superior charge carrier (hole) mobilities were observed in samples with nucleated seeds compared to controls with 0% nucleated P3HT and 100% nucleated P3HT. UV–vis spectral analysis identified that an intermediate degree of solution aggregation (15–20%) is most conducive to enhanced charge transport. The role of intrachain and interchain ordering and alignment on the mesoscale and macroscale is characterized via X-ray scattering, atomic force microscopy, and optical microscopy techniques. The results presented here provide a framework to enable in situ control of the nucleation and growth process to achieve targeted solution state properties resulting in reliable and reproducible performance when the solutions are used for device fabrication.

Observation of Stepwise Ultrafast Crystallization Kinetics of Donor–Acceptor Conjugated Polymers and Correlation with Field Effect Mobility

“…The crystallization kinetics of polymeric materials relies on many factors, including chain rigidity, molecular weight, and preexisting microstructures. 21,33 Isothermal crystallization studies have been demonstrated as a powerful method for analyzing the crystallization kinetics of polymers. 36,37 However, such studies for conjugated polymers are challenging because their strong tendency to crystallize makes it difficult to reach a truly amorphous state in which controlled annealing can be carried out.…”

“…Using morphological characterization methods, people have observed the improved crystallization in P3HT films by introducing aggregations in P3HT solutions through ultrasonication and low-dose UV irradiation. 21,25,55,56 Here, we explored the impact of such preformed H-crystallites on the crystallization behaviors in DPP-based polymers using thermal characterizations enabled by FSC.…”

“…Conjugated polymers with interesting optical, electrical, and mechanical properties are strongly desired for a vast range of applications including flexible light-emitting diodes, printable photovoltaics, wearable electronics, and sensory technologies. − These polymers have chemical structures endowed with a π-electron conjugation along the polymer backbone and usually form into semicrystalline microstructures. Their chemical structures primarily dictate their solid-state properties, − while the physical packing structures of polymer chains also play a critical role. − For example, improved crystallinity in conjugated polymer films through annealing can lead to more than 1 order of magnitude improvement in charge-transport mobility, − while the suppressed growth of large crystallites in conjugated polymers results in significant improvement in mechanical stretchability. , However, the crystallization behaviors (e.g., the crystallization kinetics and the crystal growth) of conjugated polymers and their correlations with the chemical and morphological structures are still awaiting further understanding. − …”

“…The evolution of conjugated polymer crystallization typically consists of two processes: (1) the formation of primary nuclei or aggregates and (2) the crystal growth. There have been many processing methods developed to modulate the crystallization of conjugated polymers, such as thermal annealing, , pretreatments of polymer solutions, , and advanced deposition methods (e.g., shear coating, , template modification, and slow solvent evaporation). During these crystallization processes, the complex intra/intermolecular forces (e.g., intrachain flexibility constraints and interchain π–π interactions) and pre-existing structure history (e.g., local aggregation and anisotropic crystallites) will both impact the evolution of the crystal structures and, thus, influence the solid-state properties (e.g., electrical, mechanical).…”

Optimizing Morphology to Trade Off Charge Transport and Mechanical Properties of Stretchable Conjugated Polymer Films

“…Moreover, the chain conformations of emerging D–A copolymers are more complex than those in homotype conjugated polymers because multiple noncovalent interactions (i.e., π–π interactions, hydrogen bonding, and heteroatom interactions arising from π-conjugated backbones or functional groups) are involved. Therefore, it is difficult to propose general models to predict the crystallization process of rigid conjugated polymers. − …”