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The energetic driving force for electron transfer must be minimized to realize efficient optoelectronic devices including organic light-emitting diodes (OLEDs) and organic photovoltaics (OPVs). Exploring the dynamics of a charge-transfer (CT) state at an interface leads to a comprehension of the relationship between energetics, electron-transfer efficiency, and device performance. Here, we investigate the electron transfer from the CT state to the triplet excited state (T1) in upconversion OLEDs with 45 material combinations. By analyzing the CT emission and the singlet excited-state emission from triplet-triplet annihilation via the dark T1, their energetics and electron-transfer efficiencies are extracted. We demonstrate that the CT→T1 electron transfer is enhanced by the stronger CT interaction and a minimal energetic driving force (<0.1 eV), which is explained using the Marcus theory with a small reorganization energy of <0.1 eV. Through our analysis, a novel donor-acceptor combination for the OLED is developed and shows an efficient blue emission with an extremely low turn-on voltage of 1.57 V. This work provides a solution to control interfacial CT states for efficient optoelectronic devices without energy loss.

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Optical biosensors based on plasmonic sensing schemes combine high sensitivity and selectivity with label-free detection. However, the use of bulky optical components is still hampering the possibility of obtaining miniaturized systems required for analysis in real settings. Here, a fully miniaturized optical biosensor prototype based on plasmonic detection is demonstrated, which enables fast and multiplex sensing of analytes with high- and low molecular weight (80 000 and 582 Da) as quality and safety parameters for milk: a protein (lactoferrin) and an antibiotic (streptomycin). The optical sensor is based on the smart integration of: i) miniaturized organic optoelectronic devices used as light-emitting and light-sensing elements and ii) a functionalized nanostructured plasmonic grating for highly sensitive and specific localized surface plasmon resonance (SPR) detection. The sensor provides quantitative and linear response reaching a limit of detection of 10-4 refractive index units once it is calibrated by standard solutions. Analyte-specific and rapid (15 min long) immunoassay-based detection is demonstrated for both targets. By using a custom algorithm based on principal-component analysis, a linear dose-response curve is constructed which correlates with a limit of detection (LOD) as low as 3.7 µg mL-1 for lactoferrin, thus assessing that the miniaturized optical biosensor is well-aligned with the chosen reference benchtop SPR method.

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Efficient charge transfer between organic semiconductors and electrode materials at electrode interfaces is essential for achieving high-performance organic optoelectronic devices. For efficient charge injection and extraction at the electrode interface, an interlayer is usually introduced between the organic active layer and electrode. Here, a simple and effective approach for further improving charge transfer at the organic active layer-interlayer interface was presented. Treatment of the zinc oxide (ZnO) interlayer, a commonly used n-type interlayer, with a fullerene-based self-assembled monolayer (SAM) effectively improved electron transfer at the organic-ZnO interface, without affecting the morphology and crystalline structure of the organic active layer on the cathode interlayer. Furthermore, this treatment reduced charge recombination in the device, attributed to the improved charge extraction and reduction of undesirable ZnO-donor polymer contacts. The photocurrent density and power conversion efficiency of organic solar cells employing the fullerene-SAM-treated interlayer were ~10% higher than those of the device employing the nontreated interlayer. This improvement arises from the enhanced electron extraction and reduced charge recombination.

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Transparent electrodes (TEs) are important components in organic optoelectronic devices. ITO is the mostly applied TE material, which is costly and inferior in mechanical performance, and could not satisfy the versatile need for the next generation of transparent optoelectronic devices. Recently, many new TE materials emerged to try to overcome the deficiency of ITO, including graphene, ultrathin metal, and oxide-metal-oxide structure. By finely control of the fabrication techniques, the main properties of conductivity, transmittance, and mechanical stability, have been studied in the literatures, and their applicability in the potential optoelectronic devices has been reported. Herein, in this work, we summarized the recent progress of the TE materials applied in optoelectronic devices by focusing on the fabrication, properties, such as Graphene, ultra-thin metal film, and metal oxide and performance. The advantages and insufficiencies of these materials as TEs have been summarized and the future development aspects have been pointed out to guide the design and fabrication TE materials in the next generation of transparent optoelectronic devices.

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Organic semiconductor materials have been widely used in various optoelectronic devices due to their rich optical and/or electrical properties, which are highly related to their excited states. Therefore, how to manage and utilize the excited states in organic semiconductors is essential for the realization of high-performance optoelectronic devices. Triplet-triplet annihilation (TTA) upconversion is a unique process of converting two non-emissive triplet excitons to one singlet exciton with higher energy. Efficient optical-to-electrical devices can be realized by harvesting sub-bandgap photons through TTA-based upconversion. In electrical-to-optical devices, triplets generated after the combination of electrons and holes also can be efficiently utilized via TTA, which resulted in a high internal conversion efficiency of 62.5%. Currently, many interesting explorations and significant advances have been demonstrated in these fields. In this review, a comprehensive summary of these intriguing advances on developing efficient TTA upconversion materials and their application in optoelectronic devices is systematically given along with some discussions. Finally, the key challenges and perspectives of TTA upconversion systems for further improvement for optoelectronic devices and other related research directions are provided. This review hopes to provide valuable guidelines for future related research and advancement in organic optoelectronics.

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Aggregation induced emission (AIE) luminogens (AIEgens) have great potential in the field of organic optoelectronic devices because of their highly efficient emission property in solid state. For example, high efficiency organic light-emitting diodes (OLEDs) based on AIEgens have been developed successfully. Some AIEgens also show good photovoltaic response properties for organic solar cells (OSCs) and organic photodetectors (OPDs), and lasing properties for optically pumping organic lasers (OLs). The review will cover the status and prospects of AIEgens in OLEDs, OLs, OSCs and OPDs. It is expected that AIEgens will become an important organic optoelectronic material system in the future.

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In order to achieve a wider organic light-emitting diode (OLED) commercial popularity, solution processing inverted polymer light-emitting diode (iPLED) is a trend for further development, but there is still a gap for solution processing devices to achieve commercialization. The improvement of the performance iPLEDs is a research topic of intense current interest. The modification of the cathode interface layer of poly[(9,9-bis(3'-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PF-NR2) can greatly improve the performance of the devices. However, the electron transportation of the cathode interface layer of PF-NR2 films is currently poor, and there is substantial interest in improving its electron transportation to further enhance the performance of organic optoelectronic devices. In this paper, gold nanoparticles (Au NPs) with a particle size of 20 nm were prepared and doped into the interface layer PF-NR2 at a specified ratio. The electron transportation of the interface layer of PF-NR2 was greatly improved, as judged by conductive atomic force microscopy measurements, which is due to the excellent conductivity of Au NPs. Herein, we demonstrate improved electron transportation of the interface layer by doping Au NPs in PF-NR2 film, which provides important and practical theoretical guidance and technical support for the preparation of high performance organic optoelectronic devices.

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Use of the intrinsic optoelectronic functions of organic semiconductor films has not yet reached its full potential, mainly because of the primitive methodology used to control the molecular aggregation state in amorphous films during vapor deposition. Here, a universal molecular engineering methodology is presented to control molecular orientation; this methodology strategically uses noncovalent, intermolecular weak hydrogen bonds in a series of oligopyridine derivatives. A key is to use two bipyridin-3-ylphenyl moieties, which form self-complementary intermolecular weak hydrogen bonds, and which do not induce unfavorable crystallization. Another key is to incorporate a planar anisotropic molecular shape by reducing the steric hindrance of the core structure for inducing π-π interactions. These synergetic effects enhance horizontal orientation in amorphous organic semiconductor films and significantly increasing electron mobility. Through this evaluation process, an oligopyridine derivative is selected as an electron-transporter, and successfully develops highly efficient and stable deep-red organic light-emitting devices as a proof-of-concept.

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Photoinduced space-charges in organic optoelectronic devices, which are usually caused by poor mobility and charge injection imbalance, always limit the device performance. Here we demonstrate that photoinduced space-charge layers, accumulated at organic semiconductor-insulator interfaces, can also play a role for photocurrent generation. Photocurrent transients from organic devices, with insulator-semiconductor interfaces, were systematically studied by using the double-layer model with an equivalent circuit. Results indicated that the electric fields in photoinduced space-charge layers can be utilized for charge generation and can even induce a photovoltage reversal. Such an operational process of light harvesting would be promising for photoelectric conversion in organic devices.

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In insect eyes, ommatidia with hierarchical structured cornea play a critical role in amplifying and transferring visual signals to the brain through optic nerves, enabling the perception of various visual signals. Here, inspired by the structure and functions of insect ommatidia, a flexible photoimaging device is reported that can simultaneously detect and record incoming photonic signals by vertically stacking an organic photodiode and resistive memory device. A single-layered, hierarchical multiple-patterned back reflector that can exhibit various plasmonic effects is incorporated into the organic photodiode. The multiple-patterned flexible organic photodiodes exhibit greatly enhanced photoresponsivity due to the increased light absorption in comparison with the flat systems. Moreover, the flexible photoimaging device shows a well-resolved spatiotemporal mapping of optical signals with excellent operational and mechanical stabilities at low driving voltages below half of the flat systems. Theoretical calculation and scanning near-field optical microscopy analyses clearly reveal that multiple-patterned electrodes have much stronger surface plasmon coupling than flat and single-patterned systems. The developed methodology provides a versatile and effective route for realizing high-performance optoelectronic and photonic systems.

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In this study, we synthesized three conjugated polymer electrolytes (CPEs) with different conjugation lengths to control their dipole moments by varying spacers. P-type CPEs (PFT-D, PFtT-D, and PFbT-D) were generated by the facile oxidation of n-type CPEs (PFT, PFtT, and PFbT) and introduced as the hole-transporting layers (HTLs) of organic solar cells (OSCs) and polymer light-emitting diodes (PLEDs). To identify the effect on electrode work function tunability by changing the molecular conformation and arrangement, we simulated density functional theory calculations of these molecules and performed ultraviolet photoelectron spectroscopy analysis for films of indium tin oxide/CPEs. Additionally, we fabricated OSCs and PLEDs using the CPEs as the HTLs. The stability and performance were enhanced in the optimized devices with PFtT-D CPE HTLs compared to those of PEDOT:PSS HTL-based devices.

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Both single-junction and tandem organic photovoltaic cells have been well developed. A tandem cell contains two junctions with a charge recombination layer (CRL) inserted between the two junctions. So far, there is no detailed report on how the device will perform that contains two junctions but without a CRL in between. In this work, we report the photocurrent spectra and photovoltage output of the devices that contains two bulk-heterojunctions (BHJ) stacked directly on top of each other without a CRL. The top active layer is prepared by transfer printing. The photocurrent response spectra and photovoltage are found to be sensitive to stacking sequence and the selection of electron acceptors. The open-circuit voltage of the devices (up to 1.09 V) can be higher than the devices containing either junction layer. The new phenomenon in the new device architecture increases the versatility of the optoelectronic devices based on organic semiconductors.

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Considering the peculiar topology of corannulene and extraordinary optoelectronic properties of perylene dyes, a series of hybrid corannulene-perylene dyes, namely corannulene-fused perylene-3,4-dicarboxylic acid monoimide (PMI) and corannulene-fused perylene-3,4,9,10-tetracarboxylic acid diimides (PDIs), were efficiently synthesized by a Suzuki coupling (carbon-carbon bond formation) and subsequent oxidative cyclization and photocyclization, respectively. Single crystal packing demonstrates that the solid state of the corannulene-fused PMI is arranged in back to back antiparallel dimers due to the strong dipole-dipole interactions. Integration of the corannulene unit to the perylene dyes along peri-positions makes the absorption bathochromically-shifted together with a much higher molar extinction coefficient, whereas integration of the corannulene unit to the perylene dyes along bay-positions has a much broader absorption. Strong and broad absorption properties, strong electron-accepting ability, and suitable LUMO levels close to that of [6,6]-phenyl-C61 -butyric acid methyl ester (PCBM) make hybrid corannulene-perylene dyes promising electron-acceptor materials for organic optoelectronic devices.

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Multiple-patterned nanostructures prepared by synergistically combining block-copolymer lithography with nano-imprinting lithography have been used as back reflectors for enhancing light absorption in organic optoelectronic devices. The multiple-patterned electrodes have significantly boosted the performance of organic photovoltaics and photo-transistors, owed to the highly effective light scattering and plasmonic effects, extending the range of their practical applications.