This PDF file contains the front matter associated with SPIE Proceedings Volume 7778, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Two major concerns in the world nowadays are the plastic consumption and waste. Because to the economic growth and the incessant demand of plastics in developing countries, plastics consumption is projected to increase by a factor of two to three during the actual decade¹. As an intuitive example, the amount of municipal solid waste (estimated per person per year) averages ~440 kg for China, ~550 kg for the European Union and ~790 kg for the United States, with almost 50% of the waste being electronic products and plastics^1,2. Green technology based on biodegradable/compostable materials is perceived as an ultimate goal for solving waste problems. Currently there are numerous efforts for producing compostable plastic materials for applications in daily life products, such as plastic bags and disposable dishware. When such low-end products are fabricated with compostable materials, electronics included in such goods should be also based on materials that are easily compostable.

Five core-dichlorinated naphthalene diimides (NDIs) bearing several fluoroalkyl-substituents at the imide nitrogens were synthesized, characterized and employed in organic n-channel thin-film transistors with a vacuum-deposited semiconductor layer on 110 nm thick SiO₂ (100 nm)/AlO_x (8 nm)/SAM (1.7 nm) and 5.7 nm thick AlO_x (3.6 nm)/SAM (2.1 nm) gate dielectrics. The electron mobility of the thin-film transistors under ambient conditions is as large as 1.3 cm²/Vs on the thicker gate dielectric. On the thinner gate dielectric the mobility is lower (0.4 cm²/Vs) but enables switching at gate-source voltages of only 3V. Such outstanding performance together with the feasible synthetic access to these compounds make these semiconductors highly promising for low-cost, large-area, and flexible electronics.

We introduce a new family of stable high-mobility organic π-type semiconductors based on the electron-rich 10,15- dihydro-5H-diindolo[3,2-a:3',2'-c]carbazole (triindole) extended π-conjugated system. This platform tends to form columnar stacks of the aromatic cores maximizing π-orbital overlap between adjacent molecules, thus paving the way for the one-dimensional migration of charge carriers along the columns. In addition these compounds have two different types of positions that can be functionalized independently offering the possibility of tuning their electronic properties as well as their morphology through chemical functionalization. The integration of the optimized triindole derivatives into solution processed devices as active layer is explored in this work.

Organic semiconductors are expected to play an important role in low-cost and energy-efficient electronic products, especially transistors. Our concept to improve the active materials is to introduce curvature into the polymer backbone. The beneficial contribution of the curvature is shown by a series of five isomeric polymers which demonstrate that an intermediate degree of curvature is the optimum compromise between good solubility and high order in the film. In this way, a polythiophene is developed that is easily synthesized, well soluble, exhibits high charge-carrier mobility using mild annealing conditions, and is stable under operation. When processed on a flexible substrate, it shows average mobilities as high as 0.5 cm²V^-1s^-1 .

We have investigated the electronic structure, interface formation, and thin film growth dynamics of rubrene using ultraviolet photoemission spectroscopy (UPS), inverse photoemission spectroscopy (IPES), angle-resolved photoemission spectroscopy (ARPES), and atomic force microscopy (AFM). From UPS and IPES we obtained an injection gap of 2.67 eV, which is derived from the onset separation of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), and a transport gap of 3.98 eV, which is derived from the peak separation. The ARPES results indicate that the HOMO band dispersion along Γ-X is 0.25 eV, and the electron effective mass is 1.3 times of the free electron one. These values can produce an estimate of the hole mobility of 15 Vs/cm². The investigation of the electronic structure of the interfaces between rubrene and various metals, such as Au, Ag, Al, and Ca, shows that the Fermi level shifts linearly within the band gap as a function of metal workfunction, until it is been pinned at the LUMO by a low workfunction metal like Ca. The growth morphology dependence on the film thickness, deposition rate, and substrate temperature will also be discussed.

Organic field-effect transistors exhibit operational instabilities when a gate bias is applied. For a constant gate bias the threshold voltage shifts towards the applied gate bias voltage, an effect known as the bias-stress effect. We have performed a detailed experimental and theoretical study of operational instabilities in p-type transistors with silicon-dioxide gate dielectric. We propose a mechanism in which holes in the semiconductor are converted into protons in the presence of water and a reversible migration of these protons into the gate dielectric to explain the instabilities in organic transistors. We show how redistribution of charge between holes in the semiconductor and protons in the gate dielectric can consistently explain the experimental observations. Furthermore, we explain in detail the recovery of a pres-stressed transistor on applying zero gate bias. We show that recovery dynamics depends strongly on the extent of stressing. Our mechanism is consistent with the known aspects of bias-stress effect like acceleration due to humidity, constant activation energy and reversibility.

We present an in situ vacuum measurement in the study of electrical characteristics of n-channel OFETs based on NTCDI-C8F15 semiconductors. Electron mobility of NTCDI-C8F15 OFETs was estimated as a function of the number of ML using in situ electrical measurement. The electron mobility has been observed for the thin film transistor of NTCDI-C8F15 as thin as 2 ML (~ 5.4 nm). Field-effect mobilities rapidly increase with the increase of the film thickness. Electron mobility of OFETs reaches saturation thickness (d₀) about 3.5 ML. Our experimental results indicated that the molecular layers beyond d₀ contribute little to the carrier transport in the semiconducting channel. Our experimental results have demonstrated that the grown fashion of the first few ML of NTCDI-C8F15 on the substrate strongly influences the carrier mobility, threshold voltage, and on-off ratio. Keywords: NTCDI, OFET, carrier mobility, in-situ, n-type semiconductor, monolayer

In this paper, we introduce Merck's general approach for the development of organic semiconductor formulations. We focus on solution processable materials with the idea of developing industry-compatible processes to enable mass market penetration. We give examples of Merck's formulations achieving reproducible mobilities in the region of 2 cm²/Vs in BG OTFT. We review the importance of process development for a specific application, giving examples of supporting materials and formulations needed to facilitate usage, which covers dielectric development.

PEDOT based polyelectrolyte complexes are widely used as hole injection layers in OLEDs. They are available with high and low work functions. A new polystyrenesulfonic acid free water based complex has been developed that offers easy processing. Due to its high stability it gives rise to efficient and long living devices. Small molecule semiconductors can exhibit high charge carrier mobilities due to their high crystallinity. Oligomeric semiconductor materials with mobilities >3 cm²/Vs have been synthesized using the benzothienobenzothiophene (BTBT) core.

High performance short channel OTFTs with field effect mobilities greater than 1cm²V^-1s^-1 have been developed for OLED driver applications incorporating soluble crystalline semiconductor materials. We highlight the impact of contact resistance on the mobility in these devices and show by functionalising both the source and drain contacts and channel regions in a top gate bottom contact device architecture that the mobility can be significantly improved. Our approach also includes the optimisation of solvent selection from which the semiconductor material is deposited in order to enhance crystalline domain formation.

Recent developments in high performance organic semiconductor (OSC) materials have shown charge mobilities in the range of 2 to 5 cm²/Vs. We present our progress in fabricating organic thin film transistor (OTFT) backplanes using a low temperature process (100°C maximum) and the prospects for integration into flexible displays. Discussion is made of the fabrication process using typical flat panel display equipment as well as the possibility of further device enhancement using ink jet printing technologies. We show the feasibility of achieving an average panel mobility of >1 cm2/Vs on a range of transistor array sizes. Electrical data is presented to show how the parameters of interest, (mobility, on/off ratio, Vth), vary across an array as well as some of the scaling factors that will be important for the final device architecture. Finally, we discuss how these devices have the potential for integration into a range of displays (for example, e-paper and OLEDs) for commercial exploitation.

Low cost and ecological printing methods for mass production of thin, light, flexible electronic devices incorporating organic semiconductors are key to the further integration of electronics into everyday life. In this light, we have developed an all-solution fabrication process for plastic electronics devices, in which all components of devices spontaneously assemble with desired geometry. By formation of surface molecular template composed of self-assembled monolayers, complete arrays of organic field-effect transistors including gate electrodes, source and drain electrodes, and organic semiconductor layers have been patterned from solution phase with excellent operational characteristics on a plastic substrate. This bottom-up method of device fabrication, in which the functional properties of molecules are utilized for their spontaneous assembly, may become a core technology for plastic electronics. In this paper, we describe the principles of the surface-selective deposition technique and its application to electronic device production processes.

A series of benzo[d,d]thieno[3,2-b;4,5-b]dithiophene (BTDT) derivatives, end-functionalized with phenyl (PBTDT), benzothiophenyl (BT-BTDT) were synthesized and characterized. A facile, one-pot synthesis of BTDT was developed which enables the efficient realization of a new BTDT-based semiconductor series for organic thin-film transistors (OTFTs). The crystal structure of P-BTDT was determined via single-crystal X-ray diffraction. Various combinations of surface treatment methods, substrate temperature, and deposition flux rate sequences have significant effects on device performance. Films deposited on octadecyltrichlorosilane (OTS)- treated SiO₂ substrates under properly adjusted substrate temperature and deposition flux rate achieve an efficaceous compromise between high film crystallinity and good film grain interconnectivity, resulting in good OTFT performance, with mobility greater than 0.70 cm²V^-1s^-1 and I_on/I_off greater than 10⁸.

A n-type organic semiconductor, N,N'-didodecyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C₁₂H₂₅), film crystallizes on various temperature substrates to act as active layer of organic thin-film transistors (OTFTs). The nuclear magnetic resonance 1-D hydrogen spectroscopy (1H-NMR) was used to analyze molecular structure of the PTCDI-C₁₂H₂₅ which was synthesized by us. When the transistors was fabricated on room temperature substrate, the field-effect mobility of the device was about half of that of the transistor fabricated on high temperature substrate. Furthermore, x-ray diffraction analysis gave an account that the higher temperature substrate provided better epitaxial environment for PTCDI-C₁₂H₂₅ thin film growth. The grain size of PTCDI-C12H25 thin films deposited on room temperature and 100 °C substrates were 24.8 and 35.6 nm, respectively, which analyzed by paracrystalline theory. We base that larger grain results in better carrier transport in organic films on the grain boundary model which assumed that the boundary of grain will trap charge carriers when they pass through these grains, and the quality differences of microstructural within a grain can be neglected. The PTCDI-C₁₂H₂₅ based OTFTs were achieved high performances, such as field-effect mobility of 0.10 cm²V^-1s ^-1, threshold voltage 14.5 V, on-off ratio 3.01 × 10⁶ and subthreshold swing 1.24 V/dec, when the active layer was grown under substrate temperature of 100 °C. Additionally, contact resistance analysis reveals that PTCDI-C₁₂H₂₅ thin film on 100 °C substrate has better interface between organic thin film and electrode.