Improved Performance of Organic Light-Emitting Transistors Enabled by Polyurethane Gate Dielectric.

Organic light-emitting transistors (OLETs) are multifunctional optoelectronic devices that combine in a single structure the advantages of organic light-emitting diodes (OLEDs) and organic field-effect transistors (OFETs). However, low charge mobility and high threshold voltage are critical hurdles to practical OLET implementation. This work reports on the improvements obtained by using polyurethane films as a dielectric layer material in place of the standard poly(methyl methacrylate) (PMMA) in OLET devices. It was found that polyurethane drastically reduces the number of traps in the device, thereby improving electrical and optoelectronic device parameters. In addition, a model was developed to rationalize an anomalous behavior at the pinch-off voltage. Our findings represent a step forward to overcome the limiting factors of OLETs that prevent their use in commercial electronics by providing a simple route for low-bias device operation.

A Fully Integrated Miniaturized Optical Biosensor for Fast and Multiplexing Plasmonic Detection of High- and Low-Molecular-Weight Analytes.

Optical biosensors based on plasmonic sensing schemes combine high sensitivity and selectivity with label-free detection. However, the use of bulky optical components is still hampering the possibility of obtaining miniaturized systems required for analysis in real settings. Here, a fully miniaturized optical biosensor prototype based on plasmonic detection is demonstrated, which enables fast and multiplex sensing of analytes with high- and low molecular weight (80 000 and 582 Da) as quality and safety parameters for milk: a protein (lactoferrin) and an antibiotic (streptomycin). The optical sensor is based on the smart integration of: i) miniaturized organic optoelectronic devices used as light-emitting and light-sensing elements and ii) a functionalized nanostructured plasmonic grating for highly sensitive and specific localized surface plasmon resonance (SPR) detection. The sensor provides quantitative and linear response reaching a limit of detection of 10-4 refractive index units once it is calibrated by standard solutions. Analyte-specific and rapid (15 min long) immunoassay-based detection is demonstrated for both targets. By using a custom algorithm based on principal-component analysis, a linear dose-response curve is constructed which correlates with a limit of detection (LOD) as low as 3.7 µg mL-1 for lactoferrin, thus assessing that the miniaturized optical biosensor is well-aligned with the chosen reference benchtop SPR method.

On the Nature of Charge-Injecting Contacts in Organic Field-Effect Transistors.

Organic field-effect transistors (OFETs) are key enabling devices for plastic electronics technology, which has a potentially disruptive impact on a variety of application fields, such as health, safety, and communication. Despite the tremendous advancements in understanding the OFET working mechanisms and device performance, further insights into the complex correlation between the nature of the charge-injecting contacts and the electrical characteristics of devices are still necessary. Here, an in-depth study of the metal-organic interfaces that provides a direct correlation to the performance of OFET devices is reported. The combination of synchrotron X-ray spectroscopy, atomic force microscopy, electron microscopy, and theoretical simulations on two selected electron transport organic semiconductors with tailored chemical structures allows us to gain insights into the nature of the injecting contacts. This multiple analysis repeated at the different stages of contact formation provides a clear picture on the synergy between organic/metal interactions, interfacial morphology, and structural organization of the electrode. The simultaneous synchrotron X-ray experiments and electrical measurements of OFETs in operando uncovers how the nature of the charge-injecting contacts has a direct impact on the injection potential of OFETs.

Organic Light-Emitting Transistors with Simultaneous Enhancement of Optical Power and External Quantum Efficiency via Conjugated Polar Polymer Interlayers.

Organic light-emitting transistors (OLETs) show the fascinating combination of electrical switching characteristics and light generation capability. However, to ensure an effective device operation, an efficient injection of charges into the emissive layer is required. The introduction of solution-processed conjugated polyelectrolyte (CPE) films at the emissive layer/electrode interface represents a promising strategy to improve the electron injection process by dipole formation. However, their use in optoelectronic devices also involves some limitations because of the ionic nature of CPEs. In this context, neutral conjugated polar polymers (CPPs) represent a valid alternative to CPEs because the conjugated backbones of CPPs are functionalized with polar nonionic side groups, thus avoiding ion-dependent drawbacks. By introducing a layer of polyfluorene-containing phosphonate groups underneath the metal electrodes, we here demonstrate a substantial improvement of the electron injection properties into the OLET-emissive layer and, accordingly, a more than 2-fold increased light power and a 5 times higher external quantum efficiency of p-type OLETs in comparison with reference devices without any interlayer. The great benefit of using a transparent glass substrate allowed to selectively investigate the morphological and photoluminescent characteristics of both CPE- and CPP-buried interlayers within complete OLETs by means of an optical scanning probe technique. This, together with a thorough optoelectronic characterization of the figures of merit of working light-emitting devices, allowed to disclose the origin of the improved optical performance of CPP-based devices as well as the operation mechanisms of the investigated interlayer in the corresponding OLETs.