The prospect of using low cost, high throughput material deposition processes to fabricate organic circuitry and solar cells continues to drive research towards improving the performance of the semiconducting materials utilized in these devices. Conjugated aromatic polymers have emerged as a leading candidate semiconductor material class, due to their combination of their amenability to processing and reasonable electrical and optical performance. Challenges remain, however, to further improve the charge carrier mobility of the polymers for transistor applications and the power conversion efficiency for solar cells. This optimization requires a clear understanding of the relationship between molecular structure and both electronic properties and thin film morphology. In this Account, we describe an optimization process for a series of semiconducting polymers based on an electron rich indacenodithiophene aromatic backbone skeleton. We demonstrate the effect of bridging atoms, alkyl chain functionalization, and co-repeating units on the morphology, molecular orbital energy levels, charge carrier mobility, and solar cell efficiencies. This conjugated unit is extremely versatile with a coplanar aromatic ring structure, and the electron density can be manipulated by the choice of bridging group between the rings. The functionality of the bridging group also plays an important role in the polymer solubility, and out of plane aliphatic chains present in both the carbon and silicon bridge promote solubility. This particular polymer conformation, however, typically suppresses long range organization and crystallinity, which had been shown to strongly influence charge transport. In many cases, polymers exhibited both high solubility and excellent charge transport properties, even where there was no observable evidence of polymer crystallinity. The optical bandgap of the polymers can be tuned by the combination of the donating power of the bridging unit and the electron withdrawing nature of co-repeat units, alternating along the polymer backbone. Using strong donors and acceptors, we could shift the absorption into the near infrared.

We report thin-film morphology studies of inkjet-printed single-droplet organic thin-film transistors (OTFTs) using angle-dependent polarized Raman spectroscopy. We show this to be an effective technique to determine the degree of molecular order as well as to spatially resolve the orientation of the conjugated backbones of the 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-Pentacene) molecules. The addition of an insulating polymer, polystyrene (PS), does not disrupt the π-π stacking of the TIPS-Pentacene molecules. Blending in fact improves the uniformity of the molecular morphology and the active layer coverage within the device and reduces the variation in molecular orientation between polycrystalline domains. For OTFT performance, blending enhances the saturation mobility from 0.22 ± 0.05 cm(2)/(V·s) (TIPS-Pentacene) to 0.72 ± 0.17 cm(2)/(V·s) (TIPS-Pentacene:PS) in addition to improving the quality of the interface between TIPS-Pentacene and the gate dielectric in the channel, resulting in threshold voltages of ∼0 V and steep subthreshold slopes.

Alkali-metal ions are the messengers of all living cells, governing a cascade of physiological processes through the action of ion channels. Sodium (Na +) and potassium (K +) are the two alkali metals found in human blood serum. Devices that can monitor, in real time, the concentrations of these cations in aqueous media are in demand not only for the study of cellular machinery and dysfunctions, but also to detect conditions in the human body that lead to electrolyte imbalance, such as hypernatremia, hyperkalemia or dehydration. In this work, we developed conducting polymers that respond rapidly and selectively to varying concentrations of Na + and K + in aqueous media. These polymer films, bearing crown-ether-functionalized thiophene units specific to either Na + or K + ions, generated an electrical output proportional to the cation type and concentration. Using electropolymerization, we deposited the ion-selective polymers onto microscale gold patterns and integrated them as the gate electrode of an organic electrochemical transistor (OECT). The OECT current changed with respect to the concentration of the ion to which the polymer electrode was selective. Designed as a single, miniaturized chip, the OECT enabled the selective detection of Na + and K + within a physiologically relevant range. These electrochemical ion sensors required neither a complex functionalization route to fabricate, nor ion-selective membranes or a reference electrode to operate. Such customized conducting polymers have the potential to surpass existing technologies for the detection of alkali-metal ions in aqueous media and for further development into implantable medical devices.

Light absorption in oxygenated and deoxygenated blood varies appreciably over the visible and nearinfrared spectrum. Pulse oximeters use two distinct wavelengths of light to measure oxygen saturation SpO 2 of blood. Currently, light-emitting diodes (LEDs) are used in oximeters, which need additional components to drive them and negatively impact the overall size of the sensor. In this work, we demonstrate an ambient light oximeter (ALO), which can measure photoplethysmography signals and SpO 2 using various kinds of ambient light, avoiding the use of LEDs. We combine spectral Received: ((will be filled in by the editorial staff)) Revised: ((will be filled in by the editorial staff))

Organic semiconductors are being increasingly used for a variety of biological applications, such as biochemical sensors, drug delivery, and neural interfaces. However, the poor adhesion of cells to the typically hydrophobic, neutrally charged and low surface energy of semiconducting thin films limit their use in in vitro, cell integrated bioelectronic devices. In this work, we investigate the influence of lysine side chain units incorporated in a diketopyrrolopyrrole (DPP) semiconducting polymer on neural cell adhesion and growth, as well as evaluate their function in electrical devices. Synthesis of such biofunctionalized polymers obviates the need of biological coating steps while changing the surface physiochemistry, promising for applications in bioelectronics.