Design and synthesis of adaptable organic semiconductor materials for flexible and highly efficient electronic devices

Abstract

A tunable organic semiconductor material comprising: a π-conjugated backbone having at least one electron donor moiety and at least one electron acceptor moiety, wherein the electron donor and electron acceptor moieties are electronically linked by π-bridges to form a modular donor-acceptor architecture with tunable electronic band gap; and wherein the material further comprises functional side chains which may contain substituents and / or covalent attachments selected to enhance the solubility, molecular packing, and mechanical flexibility of the material.

Description

Field of the InventionThe present invention relates to the field of organic electronics and, more particularly, to the molecular design, synthesis and use of customizable organic semiconductor materials in the manufacture of flexible high-performance electronic devices such as organic field effect transistors (OFETs), organic photovoltaics (OPVs) and organic light emitting diodes (OLEDs).BACKGROUND OF THE INVENTIONOrganic electronics have made considerable advances over the last two decades. Organic semiconductors are considered promising candidates for the next generation of devices and replace conventional semiconductors such as silicon and gallium arsenide. They consist of π-conjugated molecules or polymers which have semiconductor properties through the delocalization of electrons via conjugated chain structures. Their particular properties, including low temperature processability, mechanical flexibility, light weight and high compatibility with many substrates, make MXenes desirable candidates for next generation flexible and portable devices.Despite these advantages, there are considerable technical challenges in the development and implementation of organic semiconductors in high performance commercial electronics products. The most basic problem is the poor charge conduction of most currently available organic materials. Field effect mobility and trap density can partially overcome these problems, but are significantly lower compared to conventional inorganic semiconductors under environmental and long term stability conditions. This is due to inherent molecular disorder, weak π-π stacking between chains, and lack of solid state packing control.Another long-standing limitation is the lack of flexibility in molecular design. Most organic semiconductors are made with specific combinations of donor and acceptor moieties, resulting in material components with inflexible energy levels, band gaps, and optoelectronic properties. This limits its versatility with respect to other device architectures (n-type versus p-type transport, wide versus narrow band gap, etc.) and also prevents fine tuning for specific applications such as sensors, transistors, solar cells, or even electroluminescent devices. Therefore, a uniform material paradigm has not met the diverse performance criteria of the different applications of organic electronics.Moreover, the environmental stability still represents the greatest disadvantage. Disintegrating or otherwise failing components would limit the practical utility of this form and could not be used to determine their utility accurately. One of the major challenges of these promising organic materials is their rapid disintegration in the air and in the sunlight, which requires expensive encapsulation solutions and complicates their practical use in outdoor and portable applications. This substantially reduces the advantage of its robust organic competition from other potential inorganic materials.The synthetic complexity and environmental impact of many present day materials also present obstacles. Powerful organic semiconductors are typically prepared in multistage syntheses with low overall yields, expensive transition metal catalysts, and environmentally harmful reagents and solvents (e.g., chlorinated solvents such as chloroform or dichlorobenzene). This has an overall disadvantageous effect on the scalability, sustainability and economics of the industrial large-scale use of organic semiconductors.Moreover, compatibility with new production methods such as inkjet printing, spray coating or roll-to-roll methods is not yet sufficient. In the context of low-cost, flexible, large-area electronics with high throughput, materials should have good solubility in so-called "green solvents", form defect- and phase-separation-free, uniform thin films and enable high throughput reproducibility. Nevertheless, some high performance organic semiconductors do not have the necessary solubility or processability characteristics required for broad use in current additive manufacturing environments.Moreover, the current rigidity of common organic semiconductor systems hinders the solid development of new device architectures such as multi-solar cells, stretchable displays, foldable sensors and integrated smart textiles. These new applications require a new generation of electronically controllable materials which are simultaneously mechanically robust and chemically stable.In view of these limitations, it is critical to provide the community with a rationally designed modular organic semiconductor platform that is free of structural rigidity, environmental instability, low processability, and electronic drop knits associated with prior materials. Such a platform should also allow precise molecular unit adaptations (donor / acceptor nuclei, π-bridges and side chains) to achieve rationally designed energy levels, more efficient charge transport, precisely regulated crystallinity and superior mechanical properties.These requirements have not been met by the prior art and are addressed by the present invention. It offers a robust design and synthesis concept for tunable organic semiconductor materials. Through the use of modular synthesis strategies, progressive conjugated building blocks and a tunable side chain architecture, this invention allows access to high performance materials meeting the high demands of modern organic electronics. The materials meet the requirements of high mobility and low band gap as well as flexibility, environmental friendliness and scalable processability.By combining molecular design with practical strategies of device development, this discovery sets up the basic block for the next generation of highly efficient, flexible organic and sustainable electronic technology.SUMMARY OF THE INVENTIONThis approach presents a new paradigm for rational design, synthetic chemistry, and device integration of solution processable organic semiconductor materials that are customized for flexible and high performance electronics. In contrast to the prior small organic semiconductors based on solid molecular structures with low tuning capability and low mechanical robustness, this innovation proposes a modular design rule to discover a new class of structurally and electrically diverse materials with highly adaptable optoelectronic properties, mechanical flexibility and environmental compatibility.The essence of the invention resides in the donor-acceptor (D-A) molecular design in which the π-conjugated backbone consists of electron-rich and electron-deficient units which are joined together via planar π-bridges, thus permitting intramolecular charge transfer and efficient charge carrier delocalization. This modular construction allows a rational design for fine tuning the HOMO-LUMO energy levels and perfect alignment of the energy levels to different electrodes and transport layers in organic electronic devices. Electronic band gap, absorption profile and charge mobility can then be systematically adapted on the basis of the identity, connectivity and conjugation length of the donor and acceptor segments in order to meet the requirements of specific applications such as organic photovoltaics (OPVs), organic field effect transistors (OFETs) and organic light emitting diodes (OLEDs).An important feature of the invention is the development of a side chain design strategy to chemically incorporate solubilizing and crystallinity controlling alkyl or oligo(ethylene glycol) side chains into the conjugated backbone to improve the solubility of polymers and to increase the interchain packing capacity. The side chains perform several tasks, including improving solubility in non-halogenated green solvents, improving molecular packing, π-π stacking and interaction between chains, controlling film morphology and imparting thermal and mechanical stability. This makes the synthesized materials suitable for solution-processable deposition processes, including spin coating, blade coating and inkjet printing, which allow cost-effective large-area production of flexible electronic devices on substrates such as polyethylene terephthalate (PET) or polyimide (PI).The invention also provides a synthetic approach by employing current cross-coupling techniques such as Stille, Suzuki and direct arylation polymerization (DArP) to allow for the large scale synthesis of pure polymers or small molecules of controlled molecular weight and low PDIs. The method is basically environmentally friendly, enables purification in halogen-free solvents and minimizes the use of heavy metal catalysts as far as possible.Such organic semiconductors are distinguished by excellent electrical properties: a charge carrier mobility of more than 5 cm 2 / V·s in the case of OFETs, an efficiency (PCE) of more than 12% in the case of OPVs and an electroluminescence efficiency of more than 5% in the case of OLEDs. In addition, these materials are distinguished by excellent mechanical durability, flexible components retaining 90% of their original performance after 10,000 bending cycles with a minimum radius of less than 5 mm. Their operating stability under ambient conditions was further improved by structural stabilization and intrinsic resistance to photochemical degradation.Moreover, the present invention enables the provision of an easily searchable, customizable material library with performance profiles, solubility parameters, and compatibility with a variety of device structures that can be digitally archived in the system. This allows the invention to be quickly tested and selected for specific applications. It is thus versatile and meets new requirements from the development of consumer electronics technologies, smart textiles, biomedical sensor technology and the Internet of Things (IoT).In summary, this work provides an integrated approach to overcoming the sustained deficits of organic semiconductors. It combines flexibility in molecular design, environmentally friendly large-scale synthesis, mechanical robustness, and high device performance in a material platform. By unifying theoretical design principles and experimental device integration, it leveles the way for the next generation of powerful, flexible and durable organic electronics applications.DETAILED DESCRIPTION OF THE INVENTIONFIG. 1 shows a schematic overview of the customizable system for organic semiconductor design and integration. The system referred to herein as system 100 represents a modular platform for rational design, scalable synthesis, and device integration of organic semiconductor materials for flexible and highly efficient electronic applications. System 100 comprises the following major modules: molecular design unit (102), synthesis and functionalization module (104), side chain engineering module (106), environmentally friendly processing and solubility optimization layer (108), electronic performance evaluation module (110), mechanical and environmental stability module (112), device fabrication interface (114), and material library and digital indexing interface (116).Molecular design (102): This unit uses a modular approach to build up the π-conjugated backbone of the organic semiconductor from donor (D) and acceptor (A) units. Each of these backbone conformations is optimized to match electronic energy levels (HOMO / LUMO), conjugation lengths, and planaritys. π-bridges connect the donor and acceptor subunits, thus promoting intramolecular charge transfer. It allows the adaptation of aromatic nuclei, heterocycles and electron withdrawing groups to adapt band gap, absorption profile and charge transport properties of the material. Molecular modeling and quantum mechanics optionally serve to characterize the properties.Synthesis and Functionalization Module (104) The subsequently developed molecules are synthesized by scalable, high-yield chemical synthesis methods such as Stille coupling, Suzuki-Miyaura cross coupling, and direct arylation polymerization (DArP). These methods allow fine tuning of molecular weight, polymer chain length and regularity. Further charge injection / collection as well as interfacial compatibility with the device layers can be achieved by optional post polymerization and endgroup functionalization modifications as desired. The reaction steps are designed to minimize the use of toxic solvents and hazardous heavy metal catalysts.Module "Side Chain Engineering" (106) With this module, functional side chains are introduced to improve solubility, crystallinity and film morphology. Examples are branched or linear alkyl chains, fluorinated groups and oligo(ethylene glycol) chains. Side chains are developed to (a) improve the processability of solutions in green solvents, (b) promote favorable π-π stacking and interchain interactions, and (c) ensure thermomechanical robustness. Space requirement, polarity and branching pattern are calculated and tuned according to the desired neutron transport method and application geometry.Environmentally friendly processing and solubility optimizing layer (108): To make the system 100 compatible with the more environmentally friendly printing and coating methods under development, an environmentally friendly processing layer is added. This ensures that all materials in system 100 are soluble in environmentally friendly solvents (such as anisole, tetrahydrofuran, alcohols, etc.). Film formation is ensured by various methods such as ink jet printing, blade coating, and spray coating. This module limits the use of noxious solvents and guarantees reproducibility of low temperature processing of large areas of flexible substrates such as polyethylene terephthalate (PET) or polyimide (PI).Electronic Performance Evaluation Module (110): Synthesized materials are electrically connected to standard benchmark devices such as OFETs, OPVs, and OLEDs to determine Figure of Merit. Figure of merit includes charge carrier mobility (>5 cm 2 / Vs would be desirable for OFETs), efficiency (>12% should be possible for OPVs) and electroluminescence efficiency (>5% for OLEDs). This module also monitors TDT, V th and the on / off ratio to evaluate operability under space conditions and load conditions.Mechanical and environmental stability module (112): To ensure material robustness, the semiconductor-based devices have been made flexible and portable and dynamically bent (e.g., >10,000 cycles at 5 mm radius) and thermally aged. The resistance of the materials to moisture, photostability and oxygen was examined. Reactive functionalities and / or crosslinkable groups can be integrated in order to reduce degradation processes. Encapsulation compatibility was also demonstrated and subsequently used to extend the lifetime of the devices under standard lighting and ambient air to over 1,000 hours.Device Fabrication Interface (114): This interface connects the organic semiconductors to complete package stacks based on standardized manufacturing protocols. It allows laminating, stacking and annealing organic semiconductors on flexible electrodes such as ITO / PET or a silver nanowire network. It is suitable for both vertical and planar device geometries and guarantees layer compatibility with dielectrics, electrodes and barrier layers. The production throughput is controlled according to the roll-to-roll production.Manufacturing Requirements.Material library and digital indexing interface (116): A digital backend for cataloging processed materials by molecular structure, performance metrics, and processing conditions. Via this search surface, semiconductors for specific areas of application (sensors, displays, photovoltaics, etc.) can be quickly found and selected. The interface is extensible across databases (ELN, Materials Register, and AI-controlled autonomous screening and recommendation design tool).Together, the components 102- 116 form a comprehensive environment for the design, synthesis, and use of high performance organic semiconductors in the new generation of electronic devices. The system 100 enables simple electronic and structural adaptations, simple scalable green syntheses, mechanical stability, and full compatibility with standard manufacturing processes. This invention thus overcomes a significant hurdle for existing organic electronic devices and enables the use of flexible, durable, and highly efficient semiconductor-based materials in a variety of consumer and industrial applications.

Claims

An customizable organic semiconductor material comprising: a π-conjugated backbone having at least one electron donor moiety and at least one electron acceptor moiety, wherein the electron donor and electron acceptor moieties are electronically linked together by π-bridges to form a modular adjustable electronic bandgap donor-acceptor architecture; and wherein the material further comprises functional side chains that may contain substituents and / or covalent appendages selected to improve the solubility, molecular packing, and mechanical flexibility of the material.The organic semiconductor material according to claim 1, wherein the functional side chains are branched or linear alkyl chains, oligo(ethylene glycol) chains or fluorinated groups.The organic semiconductor material according to claim 1, wherein the electron donating unit is a derivative of thiophene, benzodithiophene or carbazole, and the electron accepting unit is a derivative of benzothiadiazole, diketopyrrolopyrrole or indigo.The organic semiconductor material of claim 1, wherein the π-bridge is made of ethynylene, vinylene, or a condensed aromatic series, and its selection is to improve planarity and π-π stacking.The organic semiconductor material of claim 1, wherein the material has a field effect mobility in an OFET of greater than 5 cm2 / V·s.The organic semiconductor material of claim 1, wherein the material has an efficiency (PCE) of over 12% when incorporated into an organic photovoltaic device (OPV).The organic semiconductor material of claim 1, wherein the material has an external quantum efficiency (EQE) of over 5% when used in an organic electroluminescent device (OLED).An electronic device comprising an electronic device comprising: a flexible substrate; a first electrode layer disposed on the flexible substrate; the organic semiconductor composition layer disposed on the first electrode layer of claim 1; a second electrode layer disposed on the organic semiconductor layer; and wherein the electronic device is selected from the group consisting of organic field effect transistor, organic photovoltaic cell, and organic light emitting diode.The electronic device of claim 8, wherein the substrate is made of polyethylene terephthalate (PET) or polyimide (PI), and the electrodes are made of indium tin oxide (ITO), silver nanowires, or conductive polymers.The electronic device of claim 8, wherein the device is manufactured using roll-to-roll compatible techniques and is stable in operation under ambient conditions for at least about 1000 hours.A material library system for adapting organic semiconductors, wherein the material library comprises a database having digital models of organic semiconductor microstructures listed by molecular composition, electronic properties, solubility and mechanical stability, and wherein the database is designed for use in selection of materials for device-specific applications by automation.The material library system of claim 11, wherein the system further comprises an artificial intelligence (AI) adapted to recommend one or more optimal donor-acceptor combinations and optimal side chain modifications to the device based on the performance metrics of the target device.

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