Sensitive detection of near-infrared (NIR) light enables many important applications in both research and industry. Current organic photodetectors suffer from low NIR sensitivity typically due to early absorption cutoff, low responsivity and/or large dark/noise current under bias. Herein, organic photodetectors based on a novel ultranarrow bandgap non-fullerene acceptor, CO1-4Cl, are presented, showcasing a remarkable responsivity over 0.5 A W-1 in the NIR spectral region (920-960 nm), which is the highest amongst organic photodiodes. By effectively delaying the onset of the space charge limited current and suppressing the shunt leakage current, the optimized devices show a large specific detectivity around 10 12 Jones for NIR spectral region up to 1010 nm, close to that of a commercial Si photodiode. The presented photodetectors can also be integrated in photoplethysmography for real-time heart rate monitoring, suggesting its potential for practical applications. Near-infrared (NIR) light usually corresponds to the region of electromagnetic radiation with wavelength spanning from about 750 nm to 1400 nm. [1] Despite being invisible to human visual perception, NIR sensing finds applications in a variety of technologies, including medical monitoring, [2] quality inspection, [3] machine vision, [4] and bio-imaging. [5] NIR sensing has been conventionally realized with detectors based on single-crystal inorganic semiconductor materials (e.g. Si, Ge, GaInAs), which typically have drawbacks including costly processing, mechanical inflexibility, and sensitivity to temperature. [6-8] Owing to the low cost, solution processing, material tunability, unique structure-property relationships and good mechanical flexibility, organic semiconductors emerged as an exciting candidate for integrated electronics, lighting, solar cells and photodetection. Particularly, photodetectors based on organic semiconductors have witnessed increasing research endeavor, Received: ((will be filled in by the editorial staff)) Revised: ((will be filled in by the editorial staff))

π-Conjugated, narrow band gap copolymers containing pyridal[2,1,3]thiadiazole (PT) were synthesized via starting materials that prevent random incorporation of the PT heterocycles relative to the backbone vector. Two regioregular structures could be obtained: in one the PTs are oriented in the same direction, and in the other the orientation of the PTs alternates every other repeat unit. Compared to their regiorandom counterparts, the regioregular polymers exhibit a 2 orders of magnitude increase of the hole mobilites, from 0.005 to 0.6 cm(2) V(-1) s(-1), as determined by field-effect transistor measurements.

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Narrow bandgap n-type molecular semiconductors are relevant as key materials components for the fabrication near-infrared organic solar cells (OSCs) and organic photodetectors (OPDs). We thus designed nearly isostructural nonfullerene electron acceptors, except for the choice of solubilizing units, which absorb from 600 to 1100 nm. Specific molecules include CTIC-4F, CO1-4F, and COTIC-4F, whose optical bandgaps are 1.3, 1.2, and 1.1 eV, respectively. Modulation of intramolecular charge transfer characteristics was achieved by replacing alkoxy groups with alkyl groups on thiophene spacers that connect an electron-rich cyclopentadithiophene core to peripheral electron-poor fragments. OSCs incorporating CTIC-4F and CO1-4F with PTB7-Th achieve power conversion efficiencies of over 10% with short-circuit current densities as high as ∼25 mA·cm–2. The same blends achieve OPD responsivities of 0.52 A·W–1 at ∼920 nm. These findings highlight outstanding opportunities to tune further molecular design so that OPDs may ultimately compete with their silicon counterparts.

Postdeposition solvent annealing of water-dispersible conducting polymers induces dramatic structural rearrangement and improves electrical conductivities by more than two orders of magnitude. We attain electrical conductivities in excess of 50 S∕cm when polyaniline films are exposed to dichloroacetic acid. Subjecting commercially available poly(ethylene dioxythiophene) to the same treatment yields a conductivity as high as 250 S∕cm. This process has enabled the wide incorporation of conducting polymers in organic electronics; conducting polymers that are not typically processable can now be deposited from solution and their conductivities subsequently enhanced to practical levels via a simple and straightforward solvent annealing process. The treated conducting polymers are thus promising alternatives for metals as source and drain electrodes in organic thin-film transistors as well as for transparent metal oxide conductors as anodes in organic solar cells and light-emitting diodes.electrical conductivity | solar cells | thin-film transistors | light-emitting diodes | polyaniline