Électronique organique

vignette| Circuit logique CMOS organique. L'épaisseur totale est inférieure à 3 μm. Barre d'échelle: 25 mm L'électronique organique est un domaine de la science des matériaux comprenant le design, la synthèse, la caractérisation et l'utilisation de petites molécules ou polymères organiques qui présentent des propriétés électroniques souhaitables comme la conductivité. Contrairement aux conducteurs et semi - conducteurs inorganiques conventionnels, les matériaux électroniques organiques sont constitués de petites molécules ou de polymères organiques. Des stratégies de synthèse pour ces matériaux ont été développées à partir de la chimie organique et des polymères. L'un des avantages espérés de l'électronique organique est son faible coût par rapport à l'électronique traditionnelle. Les propriétés intéressantes des polymères conducteurs incluent leur conductivité électrique qui peut être modifiée par la concentration de dopants. Par rapport aux métaux, ils ont une flexibilité mécanique.

Synthesis of NIR-Absorbing Squaraine Dyes and their Use in Organic Upconversion Devices

Karen Verena Strassel

Squaraines are organic dyes showing the advantages of a simple synthesis, high absorption coefficients and tunable bandgaps from the visible to the near-infrared (NIR) region. Their molecular structure is based on a polymethine chain and a donor-acceptor-donor structure that can be easily matched to the requirements of new application fields. This thesis focuses on the synthesis of squaraine dyes absorbing beyond 1000 nm and their use in organic upconversion devices. Organic dyes are widely studied and applied in optoelectronic devices such as organic solar cells, organic photodetectors (OPDs) and organic light-emitting devices (OLEDs). However, investigations so far were mainly focused on dyes absorbing and emitting in the visible range. With increasing interest in NIR-technology for biomedical and optoelectronic applications, there is a growing demand for organic NIR dyes. Here, a systematic chemical synthesis approach is used to tune the properties of benz[cd]indole substituted squaraine dyes. The donor part of the dye is modified by introducing Ï-conjugated substituents that increase the donor strength and enlarge the Ï-system. Additionally, a stronger acceptor part is introduced. A series of eight dyes is synthesized and characterized. The absorption maxima show bathochromic shifts with increasing conjugation, increasing donor strength and increasing acceptor strength. The beneficial properties of the NIR-absorbing squaraine dyes are demonstrated in organic upconversion devices with sensitivity beyond 1000 nm. The device is composed of a NIR-absorbing OPD possessing an external quantum efficiency of around 80% in the reverse bias and a visible OLED. The upconversion device converts NIR light into visible light without the need of intermediate electronics, allowing for direct NIR imaging. The organic semiconducting layers of the device stack absorb very little in the visible range. Combined with an optimized semitransparent metal top electrode, a device with an average visible transmittance of 65% is achieved. The advantages of visible transparent upconversion devices can be exploited e.g. in window-integrated electronic circuits. Another major benefit of organic electronics is the possibility to fabricate devices from solution, allowing low-cost and large-area production on flexible substrates. Here, the NIR-absorbing squaraine dye is used in upconversion devices consisting of five solution-processed layers. As emitting part, a fluorescent copolymer (super yellow)-based OLED or light-emitting electrochemical cell (LEC) is investigated. The solution-processed upconversion device converts NIR light with a wavelength of 980 nm efficiently to yellow light with a wavelength of around 575 nm, exhibiting a low turn-on voltage of 2.7 V. Replacing the OLED by a LEC allows for eliminating the sensitive calcium layer that acts as electron-injection layer. Due to the presence of ions, the LEC-based device shows a dynamic behavior, which is characterized in detail. A great deal of progress has been made with upconversion devices over the last years, but a number of challenges must be resolved to finally transform present-day prototype NIR imagers into a technology. Here, I address some of the scientific opportunities and challenges, including upconverters with sensitivity beyond 1000 nm, and visibly transparent and solution-processed devices with a narrow spectral response in the NIR.

EPFL2021

Hydrogen-Bonded Small Molecules and Polymers in Organic Electronics

Bilal Özen

Organic semiconductors are important components for applications in different fields of technology, as their advantages include the possibility of low-temperature processing as well as low-cost, large-area manufacturing based on solution-based processes, compared with inorganic counterparts. These organic materials are based on pi-conjugated molecules whose arrangements across different length scales in bulk materials are an important factor that determines their macroscopic optoelectronic properties. However, the control of their complex microstructure and morphology at the nanoscale remains challenging. In the present thesis, we investigated the use of amide hydrogen bonding as an additional structural motif to control the arrangement of pi-conjugated molecules in bulk across different length scales. In the first part, we prepared a series of hydrogen-bonded, amide-functionalized oligothiophenes together with their non-hydrogen-bonded ester analogues and studied in detail the resulting structure-property relationships. Our results showed that hydrogen-bonded bithiophenes and quaterthiophenes induced a tighter packing of the molecules as compared to their non-hydrogen-bonded analogues, resulting in a larger pi-overlap. Moreover, hydrogen bonding provided an additional driving force for a preferred formation of layered structures resulting in crystalline thin films with large domain sizes. Both of these factors resulted in an excellent performance of the thin films in field-effect transistors that is on par with that of single-crystals of related quaterthiophene derivatives. In the second part, we extended the scope to polymer semiconductors. To this end, we designed and synthesized a series of polyamides that make use of bithiophene and perylene bisimide cores as model repeat units to provide optoelectronic functionality. We have studied in detail the synergistic interplay of hydrogen bonding and pi-pi interactions and their role for the resulting materials' microstructure. As a result, we found that these materials exhibited microscopic structures similar to those of industrial-grade polyamides, providing comparable thermoplastic properties. In addition, these materials showed significant charge carrier mobility. This study may, therefore, pave the way towards polyamide-based semiconductors, with a synergistic interplay of interchain hydrogen bonding and pi-pi stacking rendering them suitable for applications in which both mechanical and optoelectronic properties play an important role.

EPFL2020

Synthesis of NIR-Absorbing Squaraine Dyes and their Use in Organic Upconversion Devices

Karen Verena Strassel

EPFL2021

Hydrogen-Bonded Small Molecules and Polymers in Organic Electronics

Bilal Özen

EPFL2020

Synthesis of NIR-Absorbing Squaraine Dyes and their Use in Organic Upconversion Devices

Hydrogen-Bonded Small Molecules and Polymers in Organic Electronics

Hydrogen-Bonded Oligothiophenes for Organic Electronics

Hydrogen-Bonded Oligothiophenes for Organic Electronics

Synthesis of NIR-Absorbing Squaraine Dyes and their Use in Organic Upconversion Devices

Hydrogen-Bonded Small Molecules and Polymers in Organic Electronics