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Materials Research Institute



From Organic Electronics to Bioelectronics & Engineering Organic Semiconductors

Date: 20 July 2016   Time: 14:30 - 17:00

From Organic Electronics to Bioelectronics
Christian Nielsen

Semiconducting materials have long played a pivotal role in the development and advancement of organic electronic applications such as organic light-emitting diodes, organic field-effect transistors and organic solar cells. More recently, semiconducting polymers have made their entry into the new field of organic bioelectronics, which broadly encompasses any application that couples a relevant function of organic electronic materials with a targeted biological event. In this context, recent endeavors have seen organic electronic materials utilized for example in biologically relevant ion sensing, ion pumps, and as transducers of neural activity.
This talk will highlight aspects of my previous work on organic electronics, covering organic photovoltaics and field-effect transistors, and discuss my journey into organic bioelectronics with an emphasis on very recent work on ion sensing in an aqueous environment using organic semiconductors and organic electrochemical transistors.
The organic electrochemical transistor (OECT), capable of transducing small ionic fluxes into electronic signals in an aqueous environment, is an ideal device to utilize in bioelectronic applications. Currently, most OECTs are fabricated with commercially available conducting poly(3,4-ethylenedioxythiophene) (PEDOT)-based suspensions and are therefore operated in depletion mode. Here, I will present a series of semiconducting polymers designed to elucidate important structure-property guidelines required for accumulation mode OECT operation. I will discuss key aspects relating to OECT performance such as ion and hole transport, electrochromic properties, operational voltage and stability. The demonstration of our molecular design strategy is the fabrication of accumulation mode OECTs that clearly outperform state-of-the-art PEDOT based devices, and show stability under aqueous operation without the need for formulation additives and cross-linkers.

Engineering Organic Semiconductors
Bob C. Schroeder

Organic semiconductors are an incredibly exciting class of materials that have had a profound impact over the last decades on our understanding of physics and materials science. But besides being a scientific curiosity, organic semiconductors have the potential to displace inorganic semiconductors as the material of choice in various technologies. In contrast to silicon based semiconductors, organic materials can be formulated into inks and subsequently printed using well established printing techniques. This makes them particularly interesting for large area applications requiring high production throughput and technologies benefiting from flexible substrates. Organic semiconductors commonly achieve hole mobilities in field effect transistors comparable to silicon ( ?1 cm2.V-1.s-1) and the best performing organic photovoltaics attain power conversion efficiencies >10%. Even though the device performances of organic semiconductors constantly improved over the years, the materials properties and processing conditions remain poorly understood.
This talk will focus on the interplay of molecular structure and materials properties, thus highlighting how rational material’s design impacts processing conditions and device performance. One of the aspects covered will focus on the morphological stability of bulk heterojunction solar cells and how the addition of fullerene derivatives can help to improve the long term device stability under operating conditions. Secondly, I will highlight the importance of side chains in conjugated polymers and how those side chains can be modified to alter either the molecular packing or the materials solubility. Whereby the molecular packing has a significant impact on the charge transport properties in organic field effect transistors, the material solubility is key to enable inkjet printing of semiconducting polymers.

Location:  David Sizer Lecture Theatre, Francis Bancroft Building
Contact:  Christian Nielsen & Bob Schroeder
Telephone:  020 7882 6014