The use of organic semiconductors in electronic devices have raised a lot of attention over the last few years. Organic semiconductors will not compete with inorganic counterparts but might open a novel niche market including a wide range of new applications. The inherent properties of organic materials makes them suitable for the fabrications of flexible and biocompatible devices. Further, due to the easy processability of organic semiconductors from solution, these materials can, in principle, be printed over large areas using simple and low-cost techniques.There are a variety of techniques for depositing organic semiconductors from solution such as spin-coating, drop-casting, dip-coating, blade-coating, etc. However, not all these techniques are compatible with roll-to-roll systems, so they are hardly scalable. This can be considered a clear bottle neck that hinders the market entry of these organic devices.
Recently, we developed a solution-shearing technique, namely bar-assisted meniscus shearing (BAMS) to deposit organic semiconductors which leads to highly crystalline and reproducible thin films. The BAMS technique consists in depositing a solution of an organic semiconductor blended with an insulating polymer between a bar and a hot plate creating a meniscus. Afterwards, the meniscus is dragged at a fixed temperature and velocity. BAMS achieves in one-step the fabrication of films that meet the requirements for manufacturing organic field-effect transistors (OFETs): high mobility, stability in air and water, long-term stability and isotropic properties. The combination of the device properties together with the low-cost of the materials and the processing steps involved represents an important step forward towards organic devices for real applications.
In the framework of this LAB-TECH project, a home-made equipment was designed and fabricated to customize the BAMS technique. The designed and fabricated machine allows the adjustment of a wide range of parameters through a software such as the speed of the moving stage, the substrate temperature and the bar height at micrometer scale. In this way, the experimental parameters for the deposition of different organic semiconductors can be adjusted and optimized for each material. Additionally, it has also been installed a video camera with a polarizer that allows visualizing the domains of polycrystalline films.
During this project, we have also studied the viability of applying the BAMs technique to print benchmark organic semiconductors. We demonstrated that by applying very similar formulations and experimental conditions for printing them, highly reproducible and uniform crystalline films exhibiting high OFET performance are successfully achieved with all these materials. The mobility values are state-of-the-art values, and could be considered as exceptional taking into account the low-cost and fast speed of the BAMS technique. Thus, we can unambiguously affirm that this technique is versatile and can be applied to a wide range of materials, making it quite universal. On the other hand, tuning the deposition parameters, such as the coating speed or the substrate temperature, we have a control of the polymorphism of the organic semiconductor, which is crucial to fabricate highly reproducible devices.
The protection of the intellectual property is currently ensured by the submission of the PCT patent to the EU Patent Office which was realized during the execution of this project.
Further, the business plan carried out related to the BAMS technique suggests to launch an effective marketing campaign addressed towards a specific list of potential customers interested towards the licensing of the patent, the manufacturing of prototypes and, eventually, to some research labs in order to fully exploit the great commercial potential of the BAMS technique. In this direction, we have contact with manufacturer companies of roll-to-roll coating machines and technological centers to meet joint interests and seek for some applications.
In summary, this project has been fundamental to fabricate a customized equipment to develop a prototype for applying the BAMS technique that allows to control all the key parameters and that it is compatible with up-scaling. In addition, we have made the first steps to try to commercialize the technique in the near future.
