Additive-Stabilized Polymer Electronics Manufacturing (ASPEM)

Organic semiconductors have been the subject of focussed research efforts for more than two decades. By investigating a wide range of conjugated polymers as well as molecular materials, molecular structure-property relationships have become understood in detail. This has resulted in a spectacular improvement in materials and device performance: As an example, in the mid 1990's organic semiconductors exhibited field-effect mobilities in transistors of less than 10^-2-10^-3 cm2/Vs, which were at least two orders of magnitude lower than those of industry standard amorphous silicon transistors, that are used in liquid crystal display applications and exhibit mobilities of 1 cm2/Vs. Today state-of-the-art organic transistors reach mobilities of 2-5 cm2/Vs for polymers and 5-15 cm2/Vs for molecular systems. Similarly, the power conversion efficiency of organic solar cells has increased to 14-15% due to availability of improved materials, in particular the development of non-fullerene acceptors. As a result organic semiconductors and conjugated polymers are now an emerging technology in a broad range of applications: Organic light-emitting diodes have become an established display technology for high-end smart phones and TVs. The performance of polymer solar cells cannot compete yet with silicon solar cells for power generation applications, but for indoor energy harvesting organic solar cells are already competitive. Polymer-based OFETs have found niche applications, including flexible e-paper displays. Over the last two years due to the commercial availability of higher mobility materials the outlook for mass market application has improved: More advanced display applications, such as LCD displays, as well as non-display applications, such as X-ray imaging and fingerprint sensing have become technologically feasible and are attracting serious industrial interest and investment.
One of the technology challenges that has, however, not been fully addressed yet is operational reliability: Despite significant progress it would be fair to say that neither OLEDs nor organic solar cells match the impressive reliability of inorganic semiconductor based technologies that in many cases exceed 5-10 years of product lifetime. Also the threshold voltage stability of OFETs during extended periods of operation is inferior to those of oxide or polycrystalline silicon transistors, which exhibit threshold voltage shifts of less than 0.5V during continuous driving over an extended period.
The proposed project is based on a recent technology breakthrough: We have discovered that the operational stability of state-of-the-art high mobility polymer transistors can be dramatically increased by addition of a small molecular additive to the polymer film (Nikolka et al., Nature Materials 16, 356 (2017)). We propose to develop this technique for additive-stabilized polymer (ASP) films into a scalable manufacturing technology that meets the requirements for industrial manufacturing across a range of applications. Our ASP technique has the potential of significantly improving the performance and reliability of conjugated polymers to a level where they can meet similarly demanding reliability requirements as achieved with established inorganic semiconductors.

The technology developed within the proposed project will provide an industrially scalable manufacturing process for high performance and high stability, multifunctional, molecular additive-stabilized conjugated polymer (ASP) films for a range of applications in electronics, optoelectronics, sensors and energy. It might enable conjugated polymers to reach similar levels of reliability as currently achieved with established inorganic semiconductors.

The project could lead to organic transistors that do not change their characteristics when they are operated for extended periods of time at elevated temperatures. These can be used in light-weight, flexible and robust displays as well as visible and X-ray imaging and fingerprint sensing applications. The project could also enable biological sensors based on conjugated polymers that can be operated more reliably in an aqueous environment without changing their electrical baseline characteristics. These could find applications in a range of healthcare and medical diagnostics applications as well as environmental monitoring. Finally, the project could also lead to achieving a significantly reduced bulk-trap densities in conjugated polymer films. This could allow achieving much higher current densities and lower non-radiative recombination losses and improved device performance in polymer light-emitting diodes and solar cells.

Our proposed manufacturing process for ASP films is highly materials efficient and uses only environmentally benign and naturally abundant materials and will therefore have a positive impact on achieving more sustainable manufacturing of electronic devices.

The project is also likely to have significant scientific impact for the academic community. Because the ASP technique is simple and can be applied to a range of conjugated polymer materials it will enable researchers in the field to study materials with much cleaner transport properties, less affected by extrinsic charge trapping. This could lead not only to an improved scientific understanding of the more intrinsic electronic structure of conjugated polymers, but also to the discovery of further application opportunities for ASP films that are not yet contemplated in this proposal.