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.