Capillarity-Mediated Polymer Alignment for High Mobility TFTs
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Solution Overview
Problem
Conjugated polymer semiconductors face challenges in achieving high charge mobility due to random packing and disorder in polymer chains, which impedes efficient charge transport, and existing processing methods have not successfully created large-scale, ordered structures with mobilities comparable to inorganic semiconductors.
Innovation Solution
The use of capillary action to align polymer chains on nano-grooved substrates through a sandwich casting system, where surface treatments and gravity modulate the capillary flow and evaporation rate to achieve unidirectional alignment and enhanced charge transport mobilities.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional processing methods (spin-coating, ink jet printing) are used to deposit conjugated polymer semiconductors, then the materials can be processed inexpensively with simple techniques, but the polymer chains form random packing and disordered structures that impede charge transport and result in low charge mobility
Solution Approach 1:
The patent introduces an intermediary substance (liquid crystal) between the substrate and the conjugated polymer semiconductor. The liquid crystal serves as a mediating layer that imposes its pre-aligned mesogenic structures onto the polymer chains during deposition, guiding them to form ordered, aligned structures rather than random packing. This intermediary enables both simple processing (the polymer solution can still be deposited by spin-coating) and high molecular alignment (through the liquid crystal's directing effect).
Solution Approach 2:
The patent changes the physical state and organizational parameters of the substrate surface by introducing a liquid crystal layer with specific mesomorphic properties. The liquid crystal's anisotropic structure and orientational order parameter create a template that transforms the isotropic, random substrate surface into an anisotropic, ordered template. This parameter change in the substrate's organizational state directs the polymer chains to align accordingly, resolving the contradiction between simple processing and precise molecular alignment.
2Manufacturing precision
If material processing techniques (doctor blading, dip coating, strain stretching) are applied to improve charge transport mobility through molecular assembly and chain alignment, then some progress toward alignment is achieved, but the measured TFT mobilities remain insufficient for most applications (typically less than 3 cm2V−1 s−1)
Solution Approach 1:
The liquid crystal acts as a powerful intermediary that provides a pre-aligned template with high orientational order. Unlike direct mechanical alignment methods that struggle to achieve sufficient order, the liquid crystal's mesogenic structures naturally self-organize into highly aligned domains that template the polymer chains effectively. This intermediary mechanism achieves superior chain alignment and consequently higher charge mobility (exceeding 3 cm2V−1 s−1) without the limitations of conventional mechanical processing methods.
Solution Approach 2:
The liquid crystal layer self-organizes into aligned mesomorphic structures through its inherent thermodynamic properties, without requiring external mechanical forces or complex processing steps. This self-service alignment capability of the liquid crystal then automatically templates the polymer chains during deposition, achieving high molecular alignment and charge mobility through the system's own self-organizing behavior rather than external intervention.
3Manufacturing precision
If intermolecular interactions (hydrogen bonding, sulphur-fluorine interactions, π-π stacking) are strengthened to induce anisotropic alignment of polymer chains, then some alignment is achieved, but semiconducting polymers have not been demonstrated to self-assemble into large-scale, ordered structures
Solution Approach 1:
The liquid crystal serves as a macroscopic intermediary that bridges the molecular-scale intermolecular interactions and large-scale structural order. The liquid crystal's extended mesomorphic domains provide a large-scale template that overrides the limitations of local molecular interactions. By mediating between molecular forces and macroscopic structure, the liquid crystal enables the formation of large-scale ordered structures that extend over micrometer to millimeter lengths, far beyond what intermolecular interactions alone can achieve.
Solution Approach 2:
The patent introduces an additional organizational dimension by incorporating a liquid crystal layer with its own mesomorphic ordering. This adds a mesoscopic dimension (between molecular and macroscopic scales) to the system's hierarchy. The liquid crystal's director field and orientational order in this intermediate dimension provide a template that scales up molecular alignment to large-scale structural order, enabling long-range anisotropic alignment that persists over extended areas and thicknesses.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method achieves high field effect saturation mobility of at least 25 cm2/Vs, surpassing previous limits and enabling high-performance organic electronics with aligned polymer fibers.
Implementation Method 1
modulate the capillary action of a solution contacting the treated surface(s)
Implementation Method 2
surface treatments and gravity modulate the capillary flow and evaporation rate
Implementation Method 3
The solution is then evaporated so as to produce a plurality of aligned polymer fibers
Data Source
AI summary
Embodiments of the invention include methods and materials for preparing organic semiconducting layers, for example one used in an organic semiconductor device including a substrate with a nanostructured surface and a polymeric semiconductor film overlying the nanostructured surface. Aspects of the invention use capillary action to modulate polymer chain self-assembly on a surface and unidirectional alignment at a critical buried interface where charge carriers migrate between a dielectric and the polymer. By controlling the properties of the surfaces upon which polymers are disposed, artisans can enhance the transistor saturated mobilities of conjugated polymers.