their use in large-scale applications. [2] Thus, a second generation of solar cells based on other inorganic materials, such as cadmium telluride (CdTe)/cadmium indium gallium diselenide (CIGS), have been developed; however, their practical applications are restricted by the toxi city and scarcity of the materials, along with their high production cost. [3,4] Consequently, OSCs, dye-sensitized solar cells (DSSCs), [5,6] and perovskite solar cells (PSCs) [7-9] have been developed, which are considered as third-generation SCs. Among the solar cells of the third generation, OSCs received significant attention due to their flexibility, low cost, and ease of fabrication, [10] which combined with their high efficiency, significantly contribute to the commercialization of FOSCs. Mass production of flexible OSCs is possible by using a roll-to-roll process, which enables the fabrication of wearable devices. [11,12] Potential applications of FOSCs include wearable devices, [13] space applications, [14] rechargeable bags and tents, and solar airships. One of the main components for fabricating FOSCs is TCEs, which play a key role in achieving high-performance OSCs, where current and light transmissions are simultaneously enabled. [15] Generally, the following characteristics are required for achieving a high-performance transparent electrode: [16-18] 1) high optical transmittance for permitting photons to reach and be absorbed within the active layer; 2) low sheet resistance for decreasing the resistance of solar cells; 3) low surface roughness for avoiding electrical shortage In this review, silver nanowires (AgNWs) are introduced, as the primary material to replace indium tin oxide for fabricating cost-effective flexible organic solar cells (FOSCs), because of their remarkable solution-processing, flexibility, transparency, and conductivity, along with their enhanced properties in terms of light-scattering, plasmonic effects, and transmittance in the near infrared region. The drawbacks of AgNWs, particularly their high roughness, low adhesion to substrates, atmospheric corrosion, degradation under UV and visible light, and poor contact at wire-wire junctions, must be resolved prior to their use in commercial FOSCs applications. Herein, comparisons among all candidates (e.g., graphene, carbon nanotubes, metal grids, and conducting polymers), along with a report of all recent progress in addressing these issues for using AgNWs as flexible transparent conductive electrodes (TCEs), are discussed. In addition, recent publications on the fabrication of highly efficient FOSCs based on AgNWs are summarized. The discussed issues regarding AgNWs-TCEs apply not only to FOSCs, but can be generalized for other third-generation solar cells, such as perovskite solar cells and dye-sensitized solar cells; additionally, they provide insight for other optoelectronic applications, such as organic light-emitting diodes, liquid crystal displays, smart windows, touch panels, and heaters.

Four samples of transparent conductive films with different numbers of silver nanorings per unit area were produced. The sheet resistance, transparency, and haze were measured for each sample. Using Monte Carlo simulation, we studied the electrical conductivity of random resistor networks produced by the random deposition of the conducting rings onto the substrate. Both systems of equal-sized rings, and systems with rings of different sizes were simulated. Our simulations demonstrated the linear dependence of the electrical conductivity on the number of rings per unit area. Size dispersity decreased the percolation threshold, but without having any other significant effect on the behavior of the electrical conductance. Analytical estimations obtained for dense systems of equal-sized conductive rings were consistent with the simulations.

Simple solvothermal method was used to synthesize of uniform silver nanowires with the controllable diameter (17, 20, 35, 70 and 100 nm). It is the first report on the solvothermal synthesis of ultra‐thin silver nanowires (17 nm) with the high aspect ratio (>1000). Knowing silver nanowires diameter, length and yield after synthesis are a critical step to classify them for the final goal. Up to now, although the length of nanowires can be measured with the optical microscope, but to estimate the diameter, costly high‐resolution microscopic techniques are necessary. Herein, UV/Vis spectroscopy as an easy and cost‐effective tool is introduced to evaluate the diameter and yield of nanowires. For this purpose, after synthesis and purification of silver different nanowires; from their UV/Vis spectra, a new equation for evaluation nanowires diameter was extracted. In addition, for the first time, absorption coefficients (ϵ) of nanowires with different diameter thickness were reported and a new equation to estimate absorption coefficients to calculate concentration (mg/ml) and yield of silver nanowires was extracted. These equations have good agreement with real data and are independent of the length of nanowires.

Highly stable graphene suspensions in pure organic solvents, including volatile solvents such as ethanol, tetrahydrofurane, chloroform, acetone or toluene have been prepared by re-dispersion of a graphene-powder. Such re-dispersable solid is produced by precipitation or solvent elimination from graphene suspensions obtained by sonication of graphite in several organic solvent-water mixtures. Re-dispersion is feasible in a wide range of pure organic solvents, obtaining high quality few-layers graphene flakes stable in suspension for months. As a proof-of-concept, on-glass spray deposition of some of these suspensions, e.g. ethanol or tetrahydrofuran, results on electrically conductive transparent coatings. These results suggest industrial potential use of the scalable technology here developed to fabricate low-cost devices with many different potential applications.

Low‐cost and high yield silver nanorings with the uniform ring diameter of 15±5 μm and thickness of 120±20 nm were synthesized via a simple solvothermal method. Based on our knowledge, this is the first time that a solvothermal method is used to prepare silver nanorings. Herein, by using ammonium salts as additive salts in the presence of pressure (150 kPa) inside the reactor, the reproducibility and yield of nanorings increased. The prepared silver nanorings easily dispersed in ethanol and have been coated by spray method on PET substrate to make flexible transparent conductive films (TCF). The film based on nanorings was shown better opto‐electrical properties (higher transparency with lower haze) in comparison with nanowires with higher aspect ratio and lower thickness, at the same sheet resistance (Rs). These results introduce silver nanorings as outstanding candidates for optoelectronics applications.

Invited for the cover of this issue is the group of Mohammad‐Reza Azani and Azin Hassanpour from Intercomet S.L., Madrid, Spain. The image depicts nanowires converting to nanorings with better opto‐electrical properties. Read the full text of the article at https://doi.org/10.1002/chem.201804788.

Graphene is a unique material due to its remarkable mechanical, electrical, and optical properties. [1] Although the optical properties of graphene can be exploited in a variety of applications, the use of graphene in transparent electrodes in solar cells or liquid-crystal devices [2] has rarely been explored. Therefore, modulation of its optical properties by chemically functionalizing graphene with optoelectronically active porphyrins could result in interesting multifunctional, nanoscale materials for optical and/or optoelectronic applications. To pursue this goal, enhancement of the solubility of graphene [3] through chemical functionalization is often required. The extended oxidation of graphene, which produces single layers of graphene oxide (GO), has been especially useful in this regard. The resulting water-soluble nanomaterial, which contains hydroxyl, epoxide, and carboxylic groups, [4] offers a platform to explore further functionalization by means of conventional organic reactions. [5] The processability and chemical reactivity of GO allow the functionalization of GO with porphyrins from different perspectives. To date, graphene or graphene oxide porphyrin hybrid materials have been produced by supramolecular interaction of porphyrins with graphene/GO and by covalent attachment of porphyrins to graphene/GO. Following the former strategy, several examples of protoporphyrins containing charged meso-groups have been reported to interact with reduced GO through a combination of ionic and p-p interactions. [6] In addition, neutral proto-and metalloporphyrins can interact with graphene sheets exclusively through p-p interactions. [7] Similarly, an example of neutral protoporphyrin has been reported to interact with graphene oxide through p-p interactions. [8] From another perspective, a recent work describes the use of click-chemistry procedures to covalently attach porphyrins to graphene sheets. [9] In contrast, condensations together with Suzuki coupling reactions have been applied to the covalent attachment of porphyrins to GO. [10] Herein, we present new insights that will contribute to a better understanding of the factors that should be taken into account in the area of functionalized graphene oxide. Herein, we report studies into the interaction of a series of metalloporphyrins with graphene oxide that describe the effect of different metals and meso-groups on the supramolecular attachment of porphyrins to GO. The GO used contains an O/C ratio of 0.58 and a CÀO/C=O ratio of 2. [11] These are typical values for GO obtained by standard oxidation procedures, and it contains defect-free graphene areas, together with amorphous regions and defective areas that can contain hydroxyl, epoxy, and carboxy groups. [5,12] In addition, following reported procedures for covalent functionalization of GO, we incorporated coordinating fragments (pyridines) through esterification of carboxylic groups. The results obtained suggest that the attachment of metalloporphyrins to graphene oxide through metal-ligand inter...

ABSTRACT. The solution properties of sodium n-dodecyl sulfate, as an anionic surfactant in the presence of a cationic watersoluble 5, 10, 15, 20-tetrakis (N-methylpyridinium-4-yl) porphyrin (TMPyP) has been comprehensively studied by means of conductometry, UV-vis and resonance light scattering (RLS) spectroscopies. The results represent the decreasing of critical micelle concentration of SDS solution due to increasing of TMPyP concentration. The stabilization of SDS micelle is due to neutralization of negative charge at the micelle surface. The presence of three different species of TMPyP in SDS solution has been unequivocally demonstrated: free porphyrin monomers, porphyrin monomers or aggregates bound to the micelles, and nonmicellar porphyrin/surfactant aggregates. Our results show SDS induced an aggregation in TMPyP. In fact two kinds of J-aggregations were observed: one of them for porphyrin monomers or aggregates bound to the micelles and the other for nonmicellar porphyrin/surfactant aggregates. However, the results represent the electrostatic interaction of TMPyP with SDS anion below the cmc.