Future lightweight, flexible, and wearable electronics will employ visible‐light‐communication schemes to interact within indoor environments. Organic photodiodes are particularly well suited for such technologies as they enable chemically tailored optoelectronic performance and fabrication by printing techniques on thin and flexible substrates. However, previous methods have failed to address versatile functionality regarding wavelength selectivity without increasing fabrication complexity. This work introduces a general solution for printing wavelength‐selective bulk‐heterojunction photodetectors through engineering of the ink formulation. Nonfullerene acceptors are incorporated in a transparent polymer donor matrix to narrow and tune the response in the visible range without optical filters or light‐management techniques. This approach effectively decouples the optical response from the viscoelastic ink properties, simplifying process development. A thorough morphological and spectroscopic investigation finds excellent charge‐carrier dynamics enabling state‐of‐the‐art responsivities >102 mA W−1 and cutoff frequencies >1.5 MHz. Finally, the color selectivity and high performance are demonstrated in a filterless visible‐light‐communication system capable of demultiplexing intermixed optical signals.

One of the key challenges of perovskite photovoltaics is the scalable fabrication of high‐efficiency perovskite solar cells (PSCs). Not only the scalable deposition of high‐quality perovskite thin‐films itself, but also the adjacent charge extraction layers is pivotal. In this work, PSCs based on all‐inkjet‐printed absorber and extraction layers are presented, allowing for a scalable and material‐efficient deposition. The inkjet‐printed PSCs are of p–i–n‐architecture with a precursor‐based nickel oxide hole‐transport layer, a high‐quality inkjet‐printed triple‐cation (methylammonium, formamidinium, and cesium) perovskite absorber layer and a double layer electron‐transport layer of phenyl‐C61‐butyric acid methyl ester and bathocuproine. The ink properties, inkjet parameters, and annealing procedure are optimized for each layer. PSCs with such inkjet‐printed absorber and charge carrier extraction layers demonstrate an efficiency of >17% with low hysteresis. Although printed in ambient atmosphere, the devices show excellent short‐term stability (40 h) even under elevated temperature (85 °C). These results are a promising next step on the way to fully inkjet‐printed perovskite solar cells, including both electrodes as well.

The use of biomaterials and bioinspired concepts in electronics will enable the fabrication of transient and disposable technologies within areas ranging from smart packaging and advertisement to healthcare applications. In this work, the use of a nonhalogenated biodegradable solid polymer electrolyte based on poly(ε-caprolactone-co-trimethylene carbonate) and tetrabutylammonium bis-oxalato borate in light-emitting electrochemical cells (LECs) is presented. It is shown that the spin-cast devices exhibit current efficiencies of ≈2 cd A −1 with luminance over ≈12 000 cd m −2 , an order of magnitude higher than previous bio-based LECs. By a combination of industrially relevant techniques (i.e., inkjet printing and blade coating), the fabrication of LEC devices on a cellulose-based flexible biodegradable substrate showing lifetimes compatible with transient applications is demonstrated. The presented results have direct implications toward the industrial manufacturing of biomaterialbased light-emitting devices with potential use in future biodegradable/ biocompatible electronics.

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.

The utilization of solution‐processable organic semiconducting (OSC) polymers and the development of industrial‐relevant printing techniques enable cost‐efficient fabrication of optoelectronic devices for the mass market. Yet, the adaptation of viscoelastic properties of a functional ink to the respective printing technology is challenging. One crucial parameter is the formulation of the ink, which can be adjusted by selecting the combination of solvents that are mixed with the OSC. The current study considers model functional inks composed of a poly‐phenylene‐vinylene‐based OSC and two solvents, empirically known to be good. Their quality is quantified using the Hansen solubility parameters. The influence of the composition of the solvent mixture on structural, dynamical, and rheological behavior of the ink is investigated with light scattering, viscometry, and rheometry. Although both solvents are considered good, polymer aggregation is found at all compositions. Aggregation depends on composition in a nontrivial way. For dilute and semi‐dilute inks, the effects of aggregates on the ink viscosity are hidden by the difference in viscosities of the neat solvents. For elevated concentrations, the aggregates produce a hysteresis in the shear‐dependent viscosity, which should be considered when developing a functional ink for a particular printing technique.