Dynamic luminescent labels, in which a luminescent image changes with time after ultraviolet excitation is turned off, are attractive for anticounterfeiting. A sequence of Gd2O2S:Eu3+/Ti4+ phosphors is presented in which the Ti4+ doping concentration allows the persistent emission lifetime to be varied from 1.17 ± 0.02 to 5.95 ± 0.07 s. While this persistent lifetime is tuned, the photoluminescence quantum yield remains over 46% ± 3%. A broad charge‐transfer band allows these phosphors to be excited with inexpensive and relatively safe 375 nm light‐emitting diodes. By developing patterns with phosphors that have differing persistent lifetimes, dynamic changes in the luminescent image after the excitation source is removed can be observed. For patterns made from phosphor materials that have big differences in persistent lifetimes, these dynamic changes are observable by the eye. By contrast, the dynamic changes in patterns made by phosphors with comparable persistent lifetimes (0.20 s delayed lifetime difference) are difficult to observe by the naked eye but can be easily determined by analysis of a 30‐frames‐per‐second video taken with a smartphone. Thus, these bright phosphors with tunable persistent lifetime allow both overt (observable by eye) and covert (requiring smartphone video analysis) dynamic anticounterfeiting labels to be created.
Polarized spectroscopic photodetection enables numerous applications in diverse areas such as sensing, industrial quality control, and visible light communications. Although organic photodetectors (OPDs) can offer a cost‐effective alternative to silicon‐based technology—particularly when flexibility and large‐area arrays are desired—polarized OPDs are only beginning to receive due research interest. Instead of resorting to external polarization optics, this report presents polarized OPDs based on directionally oriented blends of poly(3‐hexylthiophene) (P3HT) and benchmark polymer or nonfullerene acceptors fabricated using a versatile solution‐based method. Furthermore, a novel postprocessing scheme based on backfilling and plasma etching is advanced to ameliorate high dark‐currents that are otherwise inherent to fibrillar active layers. The resulting polarized P3HT:N2200 OPDs exhibit a broad enhancement across all principal figures of merit compared to reference isotropic devices, including peak responsivities of 70 mA W−1 and up to a threefold increase in 3 dB bandwidth to 0.75 MHz under parallel‐polarized illumination. Polarization ratios of up to 3.5 are obtained across a spectral range that is determined by the specific donor–acceptor combinations. Finally, as a proof‐of‐concept demonstration, polarized OPDs are used for photoelasticity analysis of rubber films under tensile deformation, highlighting their potential for existing and emerging applications in advanced optical sensing.
The applicability of inkjet-printed (opto-)electrical devices are hindered by their low lateral resolution, when compared to conventional techniques. The low lateral resolution is mainly caused by the flow and spreading of the functional ink on the substrate, which is determined by the substrate-ink-interaction. Recent apporaches, that confine and controll the spreading have been developed. However, they suffer from low lateral resolution or the usage of physical barriers. The later needs an adjustment of the ink or may contain an overlaid height information. Both cases are not always applicable when fabriacting functional devices. Herein we report the utilization of a surface energy patterning approach based on siloxane self-assembled monolayers. The obtained energetic differences control the flow and suppress the spreading of the ink, without creating the necessity to alter the ink composition. Furthermore this approach leads to an improved structural fidelity and printing resolution of arbitrary shapes. With that, we were able to print silver-and gold-electrodes for organic filedeffect transistors with a channel length of <25 µm, fabricating feature sizes below the footprint of a single drop. The electrical characterization of these transistors revealed that the utilization of this surface energy patterning has no negative influence on the device performance. The introduced approach facilitates the process development and improves the quality and resolution of printed features. This will facilitate the fabrication of high-quality and high resolution printed electronic devices.
Organic photodiodes (OPDs) are optical sensors combining high performance, lightweight mechanical flexibility, and processability from solution. Their fabrication by industrial printing techniques opens a wide range of innovative applications for emerging fields in sensing and the Internet of Things. They typically consist of printed multilayers with functionalities to absorb light, to extract charges, or to reduce detection noise. However, the printing of such device architecture poses a challenge as the deposition of a material can lead to disruption of film morphology or intermixing of materials if its solvent interacts with the previously deposited layer. This work proposes a process to print multilayers from the same solvent system utilizing the aerosol‐jet technique. By fine adjustment of the aerosol properties through the tube temperature (TTube), the drying time of poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) printed layers is significantly reduced. This allows its deposition onto a P3HT‐based bulk‐heterojunction (BHJ) without negatively affecting its performance. The additional printed P3HT layer, spatially extends the donor region of the BHJ, providing ideal hole extraction and simultaneous noise reduction by the blocking of injected electrons. This donor blocking layer (DBL) yields a noise reduction of two orders of magnitude in OPDs operated under −2 V reverse bias.
We investigated the fabrication of inkjet-printed SnO2 hole-blocking layers (HBLs) for organic photodiodes (OPDs). HBLs printed at different drop spacings were fabricated, and the effect of printing parameters on the layer quality was analyzed. These layers were incorporated into polymer:nonfullerene bulk-heterojunction OPDs, and their influence on the rectification, spectral responsivity, specific detectivity, and detection speed of the device was investigated. The OPDs fabricated with a drop spacing of 35 μm corresponding to a thickness of 31 ± 7 nm exhibited the best overall performance. These OPDs reached state-of-the-art performance with spectral responsivities of >0.5 A W–1, low dark current densities in the order of 5 nA cm–2, bandwidths of >2 MHz, and peak specific detectivities of ∼1011 Jones at 740 nm.
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