Mihai Irimia-Vladu

Green and biodegradable electronics

.We live in a world where the lifetime of electronics is becoming shorter, now approaching an average of several months. This poses a growing ecological problem. This brief review will present some of the initial steps taken to address the issue of electronic waste with biodegradable organic electronic materials. Many organic materials have been shown to be biodegradable, safe, and nontoxic, including compounds of natural origin. Additionally, the unique features of such organic materials suggest they will be useful in biofunctional electronics; demonstrating functions that would be inaccessible for traditional inorganic compounds. Such materials may lead to fully biodegradable and even biocompatible/biometabolizable electronics for many low-cost applications. This review highlights recent progress in these classes of material, covering substrates and insulators, semiconductors, and finally conductors.

Hydrogen‐Bonded Semiconducting Pigments for Air‐Stable Field‐Effect Transistors

Extensive intramolecular π-conjugation is considered to be requisite in the design of organic semiconductors. Here, two inkjet pigments, epindolidione and quinacridone, that break this design rule are explored. These molecules afford intermolecular π-stacking reinforced by hydrogen-bonding bridges. Air-stable organic field effect transistors are reported that support mobilities up to 1.5 cm(2)/Vs with T80 lifetimes comparable with the most stable reported organic semiconducting materials.

Exotic materials for bio-organic electronics

“Exotic” materials have become the focus of recent developments in organic electronics that envision biocompatibility, biodegradability, and sustainability for low-cost, large-volume electronic components. In this brief review, we discuss firstly the use of paper, leather, silk, hard gelatine, and bio-degradable plastics as substrates for electronic devices, and secondly smoothing agents, such as polydimethylsiloxane and aurin. Thirdly, we describe DNA and nucleobases as examples of exotic dielectrics with low dielectric losses and leakage currents as well as sufficiently high dielectric breakdown strength. Fourthly, natural, nature-inspired, and common-commodity semiconductors are presented that broaden the materials base for organic semiconductors and may inspire further work to identify semiconductors that are stable in the face of changing environmental conditions yet degradable at the end of their product lifetime. Sustainability in organic electronics, energy storage, and emerging concepts will also be reviewed briefly. Research on “exotic” organic materials may ultimately result in environmentally safe “green electronic” products.

Hydrogen-bonds in molecular solids – from biological systems to organic electronics

Hydrogen-bonding (H-bonding) is a relatively strong, highly directional, and specific noncovalent interaction present in many organic molecules, and notably is responsible for supramolecular ordering in biological systems. The H-bonding interactions play a role in many organic electrically conducting materials - in particular in those related to biology, e.g. melanin and indigo. This article aims to highlight recent work on application of nature-inspired H-bonded organic molecules in organic electronic devices. Three topics are covered in this brief review: (1) electrical and ionic conduction in natural H-bonded systems, (2) semiconducting properties of H-bonded organic pigments, and (3) exploitation of H-bonding for supramolecular assembly of organic conductors. H-bonding interactions are ubiquitous in biology, thus making the study of H-bonded organic semiconductors highly pertinent where interfacing of electronics with biological systems is desired.

Ambipolar organic field effect transistors and inverters with the natural material Tyrian Purple

Ambipolar organic semiconductors enable complementary-like circuits in organic electronics. Here we show promising electron and hole transport properties in the natural pigment Tyrian Purple (6,6’-dibromoindigo). X-ray diffraction of Tyrian Purple films reveals a highly-ordered structure with a single preferential orientation, attributed to intermolecular hydrogen bonding. This material, with a band gap of ∼1.8 eV, demonstrates high hole and electron mobilities of 0.22 cm2/V·s and 0.03 cm2/V·s in transistors, respectively; and air-stable operation. Inverters with gains of 250 in the first and third quadrant show the large potential of Tyrian Purple for the development of integrated organic electronic circuits.

Intermolecular hydrogen-bonded organic semiconductors—Quinacridone versus pentacene

Quinacridone is a five-ring hydrogen-bonded molecule analogous in structure and size to the well-known organic semiconductor pentacene. Unlike pentacene, quinacridone has limited intramolecular π-conjugation and becomes highly colored in the solid state due to strong intermolecular electronic coupling. We found that quinacridone shows a field-effect mobility of 0.1 cm2/V·s, comparable to mobilities of pentacene in similarly prepared devices. Photoinduced charge generation in single-layer quinacridone metal-insulator-metal diodes is more than a hundred times more efficient than in pentacene devices. Photoinduced charge transfer from quinacridone to C60 is not effective, as evidenced by measurements in heterojunctions with C60. Hydrogen-bonded organic solids may provide new avenues for organic semiconductor design.

Natural resin shellac as a substrate and a dielectric layer for organic field-effect transistors

Biocompatible and sustainable electronic-grade materials are integral for the development of electronics for biointegration and ‘use-and-throw’ applications. Herein we report the use of the natural resin shellac in organic field-effect transistors. Shellac was employed to cast robust and smooth substrates suitable for durable transistor devices. In addition shellac displays excellent insulating properties enabling its use as a high-quality dielectric layer for organic field-effect transistor (OFET) devices. We demonstrate that two common organic semiconductors, pentacene and C60, show hysteresis-free operation in OFETs that employ shellac both as the substrate and as dielectric material. Shellac is a fully biocompatible (even edible) material that offers many advantages for OFET fabrication, including high dielectric breakdown fields, simple solution processing from ethanol solutions, and low temperature crosslinking at 50–70 °C. This work shows that shellac as a biomaterial can enable OFET applications where biocompatibility is necessary.

Natural and nature-inspired semiconductors for organic electronics

Herein we report our recent efforts in employing natural materials and synthetic derivatives of natural molecules for organic field effect transistors (OFETs) and organic photovoltaics (OPVs). We evaluated dyes from the following chemical families: acridones, anthraquinones, carotenoids, and indigoids. These materials have proven effective in organic field effect transistors, with mobilities in the 4 × 10-4 - 0.2 cm2/V-s range, with indigoids showing promising ambipolar behavior. We fabricated complementary-like voltage inverters with high gains using indigoids. The photovoltaic properties of these materials were characterized in metal-insulator-metal (MIM) diodes, as well as in donoracceptor bilayer devices. Additionally, we have found that indigoids and Quinacridone, show long-range crystalline order due to hydrogen binding, and have considerably higher relative permittivities (ε) compared to typical organic semiconductors. Higher permittivities result in lower exciton binding energies and thus may lead to high photocurrents in photovoltaic devices.

Natural Materials for Organic Electronics

Biological materials in organic electronics stand for low-cost production of biocompatible, biodegradable, and sustainable electronic devices. In this chapter, we discuss such materials and their implementation in the fabrication of electronic circuits. We briefly introduce applications of such biocompatible and biodegradable materials for interfacing electronics with living tissue. Research on bio-organic materials may ultimately result in establishing robust, environmentally safe, “green electronics” alternatives.

Natural and nature-inspired materials in organic electronics

The emerging field of organic electronics is motivated by the notion of mass-producing cheap and sustainable electronic devices for displays, photovoltaic cells, integrated circuits, and sensors. Future large-scale application of sustainable organic electronics based on biodegradable materials would have a positive impact on the current problem of electronic waste. We have focused our work recently on exploiting natural and natureinspired materials in organic electronics applications.1–3 We have shown that devices performing at the state-of-the-art level can be fabricated entirely from inexpensive and biodegradable materials (see Figure 1).4 Our studies of natural dyes also revealed properties with interesting potential consequences for organic semiconductors, such as hydrogen bonding. That type of bonding is a relatively strong dipolar interaction present in many natural chemical systems, being responsible for the unique properties of water and the forces holding together DNA and RNA strands. Hydrogen bonding of so-called pi-conjugated molecules, where pi-pi interactions are strengthened by hydrogen bonds, yields highly ordered, high var epsilon (dielectric constant) organic films. The strong intermolecular interactions influence the dynamics of photogenerated excited states in such materials, which allow for many possibilities compared to disordered van der Waals bonded solids used in organic electronics today. Indigoid dyes represent an interesting class of organic semiconducting materials. Indigoids are among the very few known blue-colored, natural-origin chromophores. Indigo and 6,6’-dibromoindigo (Tyrian Purple) have been exploited for thousands of years as valuable dyestuffs. We found that vacuum-evaporated indigo films show high ordering with a single-crystalline texture and exceptionally high dielectric constants (in the range of 5–6). These properties translate into high carrier mobilities in indigo and Tyrian Purple. The latter, for example, demonstrates field effect mobility of 0.4cm2/Vs for holes Figure 1. An example of materials set for a biomaterials-based organic field effect transistor. This device shows well-balanced electron and hole mobilities of 1 10 2cm2/Vs and is resistant to degradation in air. Shellac is a natural polyester resin produced by beetles and harvested in Southeast Asia and India for use as a wood varnish. Tetratetracontane is an oligoethylene present in some medicinal plants. Indigo is a dye known since antiquity and is currently the most highly produced dyestuff in the world, primarily for coloring denim.