A flexible organic reflectance oximeter array.

Transmission-mode pulse oximetry, the optical method for determining oxygen saturation in blood, is limited to only tissues that can be transilluminated, such as the earlobes and the fingers. The existing sensor configuration provides only single-point measurements, lacking 2D oxygenation mapping capability. Here, we demonstrate a flexible and printed sensor array composed of organic light-emitting diodes and organic photodiodes, which senses reflected light from tissue to determine the oxygen saturation. We use the reflectance oximeter array beyond the conventional sensing locations. The sensor is implemented to measure oxygen saturation on the forehead with 1.1% mean error and to create 2D oxygenation maps of adult forearms under pressure-cuff-induced ischemia. In addition, we present mathematical models to determine oxygenation in the presence and absence of a pulsatile arterial blood signal. The mechanical flexibility, 2D oxygenation mapping capability, and the ability to place the sensor in various locations make the reflectance oximeter array promising for medical sensing applications such as monitoring of real-time chronic medical conditions as well as postsurgery recovery management of tissues, organs, and wounds.

Realization of efficient semitransparent organic photovoltaic cells with metallic top electrodes: utilizing the tunable absorption asymmetry.

Efficient semitransparent organic photovoltaic (OPV) cells are presented in an inverted geometry employing ZnS/ Ag/ WO3 (ZAW) as a top anode and ITO/ Cs2CO3 as a bottom cathode. Upon identification of the light absorption that differs depending on the illumination direction, the degree of the absorption asymmetry is tuned by varying the ZAW structure to maximize the efficiency for one direction or to balance it for both directions. Power conversion efficiency close to that of conventional opaque OPV cells is demonstrated in semitransparent cells for the ITO side illumination by taking advantage of the internal reflection occurring at the organic/ZAW interface. Cells with efficiencies that are reduced but balanced for both illumination directions are also demonstrated.

Highly Flexible Transparent Micromesh Electrodes via Blade-Coated Polymer Networks for Organic Light-Emitting Diodes.

The availability of transparent conductive thin films that exhibit mechanical flexibility and are adapted to low-cost and large-area fabrication is a major obstacle for high-performance flexible thin-film optoelectronics. Here, by combining printing, thin-film deposition, and wet-etching processes, interconnected transparent metal micromesh (TMM) electrodes are reported. Blade-coating is used to generate self-assembled polymer micromesh networks on flexible substrates. The network structures are subsequently converted into conductive metal networks. As-fabricated TMM films display a surface roughness of around 20 nm with thickness down to 50 nm. A transmittance of 86% and a conductance of 80 Ω sq-1 are achieved at the described optimal blade-coating suspension concentration. The electrodes show mechanical flexibility with no conductivity degradation with the smallest bending radius of 1 mm or at repeated bending over 3000 cycles at a bending radius of 15 mm. We successfully demonstrate organic light-emitting diodes (OLEDs) using TMM electrodes via the blade-coating technique. The printed OLEDs have a low turn-on voltage of 3.4 V and can achieve a luminance of over 4000 cd/m2 at 6.5 V. At a luminance of 100 cd/m2, the OLEDs show a current density of 7.6 mA/cm2, an external quantum efficiency (EQE) of 3.6%, and a luminous efficacy of 1.4 lm/W.

Flexible Blade-Coated Multicolor Polymer Light-Emitting Diodes for Optoelectronic Sensors.

A method to print two materials of different functionality during the same printing step is presented. In printed electronics, devices are built layer by layer and conventionally only one type of material is deposited in one pass. Here, the challenges involving printing of two emissive materials to form polymer light-emitting diodes (PLEDs) that emit light of different wavelengths without any significant changes in the device characteristics are described. The surface-energy-patterning technique is utilized to print materials in regions of interest. This technique proves beneficial in reducing the amount of ink used during blade coating and improving the reproducibility of printed films. A variety of colors (green, red, and near-infrared) are demonstrated and characterized. This is the first known attempt to print multiple materials by blade coating. These devices are further used in conjunction with a commercially available photodiode to perform blood oxygenation measurements on the wrist, where common accessories are worn. Prior to actual application, the threshold conditions for each color are discussed, in order to acquire a stable and reproducible photoplethysmogram (PPG) signal. Finally, based on the conditions, PPG and oxygenation measurements are successfully performed on the wrist with green and red PLEDs.