Vitality surveillance at distance using thin-film tandem-like narrowband near-infrared photodiodes with light-enhanced responsivity

Remote measurement of vital sign parameters like heartbeat and respiration rate represents a compelling challenge in monitoring an individual's health in a noninvasive way. This could be achieved by large field-of-view, easy-to-integrate unobtrusive sensors, such as large-area thin-film photodiodes. At long distances, however, discriminating...

Identification of the Origin of Ultralow Dark Currents in Organic Photodiodes

Organic bulk heterojunction photodiodes (OPDs) attract attention for sensing and imaging. Their detectivity is typically limited by a substantial reverse bias dark current density (Jd). Recently, using thermal admittance or spectral photocurrent measurements, Jd has been attributed to thermal charge generation mediated by mid-gap states. Here,...

High-Accuracy Photoplethysmography Array Using Near-Infrared Organic Photodiodes with Ultralow Dark Current

Reflectance oximeters based on organic photodiode (OPD) arrays offer the potential to map blood pulsation and oxygenation via photoplethysmography (PPG) over a large area and beyond the traditional sensing locations. Here, an organic reflectance PPG array based on 16 × 16 OPD pixels is developed. The individual pixels exhibit near-infrared...

Organic Photodetectors and their Application in Large Area and Flexible Image Sensors: The Role of Dark Current

Organic photodetectors (OPDs) have gained increasing interest as they offer cost-effective fabrication methods using low temperature processes, making them particularly attractive for large area image detectors on lightweight flexible plastic substrates. Moreover, their photophysical and optoelectronic properties can be tuned both at a material...

On the Origin of Dark Current in Organic Photodiodes

Minimizing the reverse bias dark current while retaining external quantum efficiency is crucial if the light detection sensitivity of organic photodiodes (OPDs) is to compete with inorganic photodetectors. However, a quantitative relationship between the magnitude of the dark current density under reverse bias (Jd) and the properties of the bulk...

Near-infrared tandem organic photodiodes for future application in artificial retinal implants

Photovoltaic retinal prostheses show great potential to restore sight in patients suffering from degenerative eye diseases by electrical stimulation of the surviving neurons in the retinal network. Herein, organic photodiodes (OPDs) sensitive to near-infrared (NIR) light are evaluated as photovoltaic pixels for future application in retinal...

Bis(arylimidazole) Iridium Picolinate Emitters and Preferential Dipole Orientation in Films

The straightforward synthesis and photophysical properties of a new series of heteroleptic iridium(III) bis(2-arylimidazole) picolinate complexes are reported. Each complex has been characterized by nuclear magnetic resonance, UV−vis, cyclic voltammetry, and photoluminescent angle dependency, and the emissive properties of each are described....

Increasing the horizontal orientation of transition dipole moments in solution processed small molecular emitters

The efficiency of organic light emitting diodes (OLEDs) can be improved by controlling the orientation of the transition dipole moment of the emitters. Currently, no effective methods exist for orienting the transition dipole moments in solution processed active layers for OLEDs. We investigate the orientation of the transition dipole moment of...

Transition dipole moment orientation in films of solution processed fluorescent oligomers: Investigating the influence of molecular anisotropy

The low light-outcoupling efficiency of organic light emitting diodes (OLEDs) is limiting their performance. Orientation of the transition dipole moment of the emitting molecules in the plane of the diodes can improve the luminance of OLEDs. While the orientation of evaporated small-molecule materials has been studied in the past few years, not...

The energy of charge-transfer states in electron donor-acceptor blends: insight into the energy losses in organic solar cells

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Compositional and electric field dependence of the dissociation of charge transfer excitons in alternating polyfluorene copolymer/fullerene blends

The electro-optical properties of thin films of electron donor-acceptor blends of a fluorene copolymer (PF10TBT) and a fullerene derivative (PCBM) were studied. Transmission electron microscopy shows that in these films nanocrystalline PCBM clusters are formed at high PCBM content. For all concentrations, a charge transfer (CT) transition is...

Photoinduced charge and energy transfer in dye-doped conjugated polymers

Conjugated polymer-molecular dye blends of MDMO-PPV (poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene]) and PF1CVTP (poly[9,9-dioctylfluorene-2,7-diyl-alt-2,5-bis(2-thienyl-1-cyanovinyl)-1-(3′,7′-dimethyloctyloxy)-4-methoxybenzene-5″,5″-diyl]) with three dipyrrometheneboron difluoride (bodipy) dyes were studied by (time-resolved)...

Triplet formation from the charge-separated state in blends of MDMO-PPV with cyano-containing acceptor polymers

Polymer blends of MDMO-PPV with three different electron accepting cyano-substituted polymers have been investigated with photoinduced absorption (PIA) spectroscopy. In these blends, an efficient photoinduced charge transfer occurs that quenches the photoluminescence and produces a significant photovoltaic effect when the blends are incorporated...

Large area liquid crystal monodomain field-effect transistors

Butyl, hexyl, and decyl derivatives of the liquid-crystalline organic semiconductor 5,5″-bis(5-alkyl-2-thienylethynyl)-2,2′:5′, 2″-terthiophene were synthesized and studied with respect to their structural, optical, and electrical properties. By means of an optimized thermal annealing scheme the hexyl and decyl compounds could be processed into...