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Organic light-emitting devices and solar cells are devices that create, manipulate and convert excited states in organic semiconductors. It is crucial to characterize these excited states, or excitons, to optimize device performance in applications like displays and solar energy harvesting. This is complicated if the excited state is a triplet because the electronic transition is ‘dark’ with a vanishing oscillator strength. As a consequence, triplet state spectroscopy must usually be performed at cryogenic temperatures to reduce competition from non-radiative rates. Here, we control non-radiative rates by engineering a solid-state host matrix containing the target molecule, allowing the observation of phosphorescence at room temperature and alleviating constraints of cryogenic experiments. We test these techniques on a wide range of materials with functionalities spanning multi-exciton generation (singlet exciton fission), organic light emitting device host materials and thermally activated delayed fluorescence type emitters. Control of non-radiative modes in the matrix surrounding a target molecule may also have broader applications in light-emitting and photovoltaic devices.

Oxygen diffusion properties in thin polymer films are key parameters in industrial applications from food packaging, over medical encapsulation to organic semiconductor devices and have been continuously investigated in recent decades. The established methods have in common that they require complex pressure-sensitive setups or vacuum technology and usually do not come without surface effects. In contrast, this work provides a low-cost, precise and reliable method to determine the oxygen diffusion coefficient D in bulk polymer films based on tracking the phosphorescent pattern of a programmable luminescent tag over time. Our method exploits two-dimensional image analysis of oxygen-quenched organic room-temperature phosphors in a host polymer with high spatial accuracy. It avoids interface effects and accounts for the photoconsumption of oxygen. As a role model, the diffusion coefficients of polystyrene glasses with molecular weights between 13k and 350k g/mol are determined to be in the range of (0.8–1.5) × 10 –7 cm 2 /s, which is in good agreement with previously reported values. We finally demonstrate the reduction of the oxygen diffusion coefficient in polystyrene by one quarter upon annealing above its glass transition temperature.

Most materials recently developed for room temperature phosphorescence (RTP) lack in practical relevance due to their inconvenient crystalline morphology. Using amorphous material systems instead, programmable luminescent tags (PLTs) based on organic biluminescent emitter molecules with easy processing and smooth sample shapes are presented recently. Here, the effective quenching of the emitter's RTP by molecular oxygen (O2) and the consumption of the excited singlet O2 through a chemical reaction represent the central features. With customized activation schemes, high‐resolution content can be written and later erased multiple times into such films, providing a versatile yet simple photonic platform for information storage. However, two important limitations remain: The immutable fluorescence of the emitters outshines the phosphorescent patterns by roughly one order of magnitude, allowing readout of the PLTs only after the excitation source is turned off. The programming of these systems is a rather slow process, where lowest reported activation times are still >8 s. Here, a material‐focused approach to PLTs with fast activation times of 120 ± 20 ms and high‐contrast under continuous‐wave illumination is demonstrated, leading to accelerated programming on industry relevant time scales and a simplified readout process both by eye and low cost cameras. Using organic room temperature phosphorescence, programmable luminescent tags (PLTs) enable multiple writing, reading, and erasing of information into or from transparent polymer films. Here, an overview of crucial parameters and material properties for the realization of PLTs is given and consecutively implemented, leading to high‐contrast PLTs with fast writing and simplified reading procedures.

Organic semiconducting molecules and colloidal quantum dots both make for excellent luminescent materials. Compared with the more established solid-state light-emitting technologies, organic LEDs and quantum-dot LEDs are in their infancy, yet they offer unique properties.

Singlet exciton fission transforms a molecular singlet excited state into two triplet states, each with half the energy of the original singlet. In solar cells, it could potentially double the photocurrent from high-energy photons. We demonstrate organic solar cells that exploit singlet exciton fission in pentacene to generate more than one electron per incident photon in a portion of the visible spectrum. Using a fullerene acceptor, a poly(3-hexylthiophene) exciton confinement layer, and a conventional optical trapping scheme, we show a peak external quantum efficiency of (109 ± 1)% at wavelength λ = 670 nanometers for a 15-nanometer-thick pentacene film. The corresponding internal quantum efficiency is (160 ± 10)%. Analysis of the magnetic field effect on photocurrent suggests that the triplet yield approaches 200% for pentacene films thicker than 5 nanometers.

White organic light-emitting diodes (OLEDs) are promising candidates for future solid-state lighting applications and backplane illumination in large-area displays. One very specific feature of OLEDs, which is currently gaining momentum, is that they can enable tunable white light emission. This feature is conventionally realized either through the vertical stacking of independent OLEDs emitting different colors or in lateral arrangement of OLEDs. The vertical design is optically difficult to optimize and often results in efficiency compromises between the units. In contrast, the lateral concept introduces severe area losses to dark regions between the subunits, which requires a significantly larger overall device area to achieve equal brightness. Here we demonstrate a color-tunable, two-color OLED device realized by side-by-side alignment of yellow and blue p-i-n OLEDs structured down to 20 μm by a simple and up-scalable orthogonal photolithography technique. This layout eliminates the problems of conventional lateral approaches by utilizing all area for light emission. The corresponding emission of the photo-patterned two-unit OLED can be tuned over a wide range from yellow to white to blue colors. The independent control of the different units allows the desired overall spectrum to be set at any given brightness level. Operated as a white light source, the microstructured OLED reaches a luminous efficacy of 13 lm W −1 at 1000 cd m − 2 without an additional light outcoupling enhancement and reaches a color rendering index of 68 when operated near the color point E. Finally, we demonstrate an improved device lifetime by means of size variation of the subunits. Organic LEDs: tunable white light Color-tunable white organic light-emitting diodes (OLEDs) with alternating blue and yellow emitters have been fabricated. These emitters are arranged in thin alternating strips just a few tens of micrometers wide and are produced by photolithography. The micro-OLED array provides color tuning of the emitted light from blue to yellow, including warm and cold white light, without any change in brightness. Developed by researchers at Dresden University of Technology in Germany, the OLED array operates with a high luminous efficacy. Unlike previous two-color devices, based on separate sub-modules, this latest design does not suffer from dark regions between emitters; its entire surface area emits light. The OLED array can be tuned to emit light with a color rendering index of 68—one of the highest values achieved for a two-emitter system.

In recent years, the organic light-emitting diode (OLED) technology has been a rapidly evolving field of research, successfully making the transition to commercial applications such as mobile phones and other small portable devices. OLEDs provide efficient generation of light, excellent color quality, and allow for innovative display designs, e.g., curved shapes, mechanically flexible and/or transparent devices. Especially their self emissive nature is a highly desirable feature for display applications. In this work, we demonstrate an approach for full-color OLED pixels that are fabricated by vertical stacking of a red-, green-, and blue-emitting unit. Each unit can be addressed separately which allows for efficient generation of every color that is accessible by superpositioning the spectra of the individual emission units. Here, we use a combination of time division multiplexing and pulse width modulation to achieve efficient color mixing. The presented device design requires only three independently addressable electrodes, simplifying both fabrication and electrical driving. The device is built in a top-emission geometry, which is highly desirable for display fabrication as the pixel can be directly deposited onto back-plane electronics. Despite the top-emission design and the application of three silver layers within the device, there is only a minor color shift even for large viewing angles. The color space spanned by the three emission sub-units exceeds the sRGB space, providing more saturated green/yellow/red colors. Furthermore, the electrical performance of each individual unit is on par with standard single emission unit OLEDs, showing very low leakage currents and achieving brightness levels above 1000 cd/m 2 at moderate voltages of around 3–4 V.

Organic light-emitting diodes (OLEDs) suffer from notorious light trapping, resulting in only moderate external quantum efficiencies. Here, we report a facile, scalable, lithography-free method to generate controllable nanostructures with directional randomness and dimensional order, significantly boosting the efficiency of white OLEDs. Mechanical deformations form on the surface of poly(dimethylsiloxane) in response to compressive stress release, initialized by reactive ions etching with periodicity and depth distribution ranging from dozens of nanometers to micrometers. We demonstrate the possibility of independently tuning the average depth and the dominant periodicity. Integrating these nanostructures into a two-unit tandem white organic light-emitting diode, a maximum external quantum efficiency of 76.3% and a luminous efficacy of 95.7 lm W −1 are achieved with extracted substrate modes. The enhancement factor of 1.53 ± 0.12 at 10,000 cd m −2 is obtained. An optical model is built by considering the dipole orientation, emitting wavelength, and the dipole position on the sinusoidal nanotexture. For organic light-emitting diodes (OLEDs) to reach their potential for lighting applications, improved light out-coupling using industry-compatible methods are required. Here, the authors report reactive ion etching-induced quasi-periodic nanostructures for improved light extraction in white OLEDs.

Precise structural control is essential for high-performance semiconductors. In organic electronics, traditional methods for tuning the dimensions of device structures often rely on cumbersome, limited-resolution processes such as shadow mask patterning, printing, or viscosity tuning. Here, we report ultraviolet (UV) irradiation in ambient conditions as a transformative approach for tuning structural parameters of organic small molecule hole transport layers (HTLs) in vertical and lateral directions. The method preserves HTL conductivity while facilitating uniform thickness reduction through synergistic photo-induced oligomerization and photo-oxidative layer shrinking. Controlled thinning applies to various organic materials. In cavity architectures, UV-treated organic photodetectors show narrowband detection from 900 to 1200 nm with a full width at half maximum down to 25 nm, and UV-treated organic light-emitting diodes exhibit 75 nm peak tunability. Moreover, this strategy permits micrometer-scale lateral patterning of HTLs. Our work opens new opportunities for precise and practical engineering for organic electronic devices. Traditional methods for tuning the dimensions of organic electronic device structures often rely on cumbersome processes with limited resolution. Here, the authors report ultraviolet irradiation in ambient conditions for tuning structural parameters for organic small molecule hole transport layers.