Covalent Triazine Frameworks and Porous Carbons: Perspective from an Azulene-Based Case.

Covalent triazine frameworks (CTFs) are among the most valuable frameworks owing to many fantastic properties. However, molten salt-involved preparation of CTFs at 400-600 °C causes debate on whether CTFs represent organic frameworks or carbon. Herein, new CTFs based on the 1,3-dicyanoazulene monomer (CTF-Azs) are synthesized using molten ZnCl2 at 400-600 °C. Chemical structure analysis reveals that the CTF-Az prepared at low temperature (400 °C) exhibits polymeric features, whereas those prepared at high temperatures (600 °C) exhibit typical carbon features. Even after being treated at even higher temperatures, the CTF-Azs retain their rich porosity, but the polymeric features vanish. Although structural de-conformation is a widely accepted outcome in polymer-to-carbon rearrangement processes, the study evaluates such processes in the context of CTF systems. A proof-of-concept study is performed, observing that the as-synthesized CTF-Azs exhibit promising performance as cathodes for Li- and K-ion batteries. Moreover, the as-prepared NPCs exhibit excellent catalytic oxygen reduction reaction (ORR) performance; hence, they can be used as air cathodes in Zn-air batteries. This study not only provides new building blocks for novel CTFs with controllable polymer/carbon features but also offers insights into the formation and structure transformation history of CTFs during thermal treatment.

Solution-processed two-dimensional materials for next-generation photovoltaics.

In the ever-increasing energy demand scenario, the development of novel photovoltaic (PV) technologies is considered to be one of the key solutions to fulfil the energy request. In this context, graphene and related two-dimensional (2D) materials (GRMs), including nonlayered 2D materials and 2D perovskites, as well as their hybrid systems, are emerging as promising candidates to drive innovation in PV technologies. The mechanical, thermal, and optoelectronic properties of GRMs can be exploited in different active components of solar cells to design next-generation devices. These components include front (transparent) and back conductive electrodes, charge transporting layers, and interconnecting/recombination layers, as well as photoactive layers. The production and processing of GRMs in the liquid phase, coupled with the ability to "on-demand" tune their optoelectronic properties exploiting wet-chemical functionalization, enable their effective integration in advanced PV devices through scalable, reliable, and inexpensive printing/coating processes. Herein, we review the progresses in the use of solution-processed 2D materials in organic solar cells, dye-sensitized solar cells, perovskite solar cells, quantum dot solar cells, and organic-inorganic hybrid solar cells, as well as in tandem systems. We first provide a brief introduction on the properties of 2D materials and their production methods by solution-processing routes. Then, we discuss the functionality of 2D materials for electrodes, photoactive layer components/additives, charge transporting layers, and interconnecting layers through figures of merit, which allow the performance of solar cells to be determined and compared with the state-of-the-art values. We finally outline the roadmap for the further exploitation of solution-processed 2D materials to boost the performance of PV devices.

Catechol-Coordinated Framework Film-based Micro-Supercapacitors with AC Line Filtering Performance.

Coordination polymer frameworks (CPFs) have broad applications due to their excellent features, including stable structure, intrinsic porosity, and others. However, preparation of thin-film CPFs for energy storage and conversion remains a challenge because of poor compatibility between conductive substrates and CPFs and crucial conditions for thin-film preparation. In this work, a CPF film was prepared by the coordination of the anisotropic four-armed ligand and CuII at the liquid-liquid interface. Such film-based micro-supercapacitors (MSCs) are fabricated through high-energy scribing and electrolytes soaking. As-fabricated MSCs displayed high volumetric specific capacitance of 121.45 F cm-3 . Besides, the volumetric energy density of MSCs reached 52.6 mWh cm-3 , which exceeds the electrochemical performance of most reported CPF-based MSCs. Especially, the device exhibited alternating current (AC) line filtering performance (-84.2° at 120 Hz) and a short resistance capacitance (RC) constant of 0.08 ms. This work not only provides a new CPF for MSCs with AC line filtering performance but also paves the way for thin-film CPFs preparation with versatile applications.

Efficient and environmental-friendly perovskite solar cells via embedding plasmonic nanoparticles: an optical simulation study on realistic device architectures.

Solution-processed, lead halide-based perovskite solar cells have recently overcome important challenges, offering low-cost and high solar power conversion efficiencies. However, they still undergo unoptimized light collection due mainly to the thin (∼350 nm) polycrystalline absorber layers. Moreover, their high toxicity (due to the presence of lead in perovskite crystalline structures) makes it necessary that the thickness of the absorber layers to be further reduced. Here we address these issues via embedding spherical plasmonic nanoparticles of various sizes, composition, concentrations, and vertical positions, in realistic halide-based perovskite solar cells. We theoretically show that plasmon-enhanced near-field effects and scattering leads to a device photocurrent enhancement up to ∼7.3% when silver spheres are embedded inside the perovskite layer. An even further enhancement, up to ∼12%, is achieved with the combination of silver spheres in perovskite and aluminum spheres inside the hole transporting layer (PEDOT:PSS). The proper involvement of nanoparticles allows the employment of much thinner perovskite layers (up to 150 nm), reducing thus significantly the toxicity. Providing the requirements related to the design parameters of nanoparticles, our study establishes guidelines for a future development of highly-efficient, environmentally friendly and low-cost plasmonic perovskite solar cells.

Resistive switching memories with enhanced durability enabled by mixed-dimensional perfluoroarene perovskite heterostructures.

Hybrid halide perovskites are attractive candidates for resistive switching memories in neuromorphic computing applications due to their mixed ionic-electronic conductivity. Moreover, their exceptional optoelectronic characteristics make them effective as semiconductors in photovoltaics, opening perspectives for self-powered memory elements. These devices, however, remain unexploited, which is related to the variability in their switching characteristics, weak endurance, and retention, which limit their performance and practical use. To address this challenge, we applied low-dimensional perovskite capping layers onto 3D mixed halide perovskites using two perfluoroarene organic cations, namely (perfluorobenzyl)ammonium and (perfluoro-1,4-phenylene)dimethylammonium iodide, forming Ruddlesden-Popper and Dion-Jacobson 2D perovskite phases, respectively. The corresponding mixed-dimensional perovskite heterostructures were used to fabricate resistive switching memories based on perovskite solar cell architectures, showing that the devices based on perfluoroarene heterostructures exhibited enhanced performance and stability in inert and ambient air atmosphere. This opens perspectives for multidimensional perovskite materials in durable self-powered memory elements in the future.

Organic solar cells with plasmonic layers formed by laser nanofabrication.

A method for the synthesis of metal nanoparticle coatings for plasmonic solar cells which can meet large scale industrial demands is demonstrated. A UV pulsed laser is utilized to fabricate Au and Ag nanoparticles on the surface of polymer materials which form the substrates for plasmonic organic photovoltaic devices to enhance their performance. Control of the particles' size and density is demonstrated. The optical and electrical effects of these embedded particles on the power conversion efficiency are examined rigorously using both experimental and computer simulation. Gold nanoparticles of particular size and spatial distribution enhance the device efficiency. Based on our findings, we propose design considerations for utilizing the entire AM1.5 spectrum using plasmonic structures towards enhancing the efficiency of polymer solar cells using broad spectrum plasmonics.

A Low-Cost and Lithium-Free Hole Transport Layer for Efficient and Stable Normal Perovskite Solar Cells.

The most widely used material as a hole-transport layer (HTL) for effective normal perovskite solar cells (PSCs) is still 2,2',7,7'-Tetrakis[N, N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (Spiro-OMeTAD), which requires heavy doping with the hydroscopic Lithium bis(trifluoromethanesulfonyl)imide (Li-ΤFSI). However, the long-term stability and performance of PCSs are frequently hampered by the residual insoluble dopants in the HTL, Li+ diffusion throughout the device, dopant by-products, and the hygroscopic nature of Li-TFSI. Due to the high cost of Spiro-OMeTAD, alternative efficient low-cost HTLs, such as octakis(4-methoxyphenyl)spiro[fluorene-9,9'-xanthene]-2,2',7,7'-tetraamine) (X60), have attracted attention. However, they require doping with Li-TFSI, and the devices develop the same Li-TFSI-derived problems. Here, we propose Li-free 1-Ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMIM-TFSI) as an efficient p-type dopant of X60, resulting in a high-quality HTL with enhanced conductivity and deeper energy levels The optimized X60:EMIM-TFSI-enabled devices exhibit a higher efficiency of 21.85% and improved stability, compared to the Li-TFSI-doped X60 devices. The stability of the optimized EMIM-TFSI-doped PSCs is greatly improved, and after 1200 hr of storage under ambient conditions, the resulting PSCs maintain 85% of the initial PCE. These findings offer a fresh method for doping the cost effective X60 as the HTL with a Li-free alternative dopant for efficient, cheaper, and reliable planar PSCs.

Two-dimensional BiTeI as a novel perovskite additive for printable perovskite solar cells.

Hybrid organic-inorganic perovskite solar cells (PSCs) are attractive printable, flexible, and cost-effective optoelectronic devices constituting an alternative technology to conventional Si-based ones. The incorporation of low-dimensional materials, such as two-dimensional (2D) materials, into the PSC structure is a promising route for interfacial and bulk perovskite engineering, paving the way for improved power conversion efficiency (PCE) and long-term stability. In this work, we investigate the incorporation of 2D bismuth telluride iodide (BiTeI) flakes as additives in the perovskite active layer, demonstrating their role in tuning the interfacial energy-level alignment for optimum device performance. By varying the concentration of BiTeI flakes in the perovskite precursor solution between 0.008 mg mL-1 and 0.1 mg mL-1, a downward shift in the energy levels of the perovskite results in an optimal alignment of the energy levels of the materials across the cell structure, as supported by device simulations. Thus, the cell fill factor (FF) increases with additive concentration, reaching values greater than 82%, although the suppression of open circuit voltage (V oc) is reported beyond an additive concentration threshold of 0.03 mg mL-1. The most performant devices delivered a PCE of 18.3%, with an average PCE showing a +8% increase compared to the reference devices. This work demonstrates the potential of 2D-material-based additives for the engineering of PSCs via energy level optimization at perovskite/charge transporting layer interfaces.

Quinone-Enriched Conjugated Microporous Polymer as an Organic Cathode for Li-Ion Batteries.

Among various organic cathode materials, C═O group-enriched structures have attracted wide attention worldwide. However, small organic molecules have long suffered from dissolving in electrolytes during charge-discharge cycles. π-Conjugated microporous polymers (CMPs) become one solution to address this issue. However, the synthesis strategy for CMPs with rich C═O groups and stable backbones remains a challenge. In this study, a novel CMP enriched with C═O units was synthesized through a highly efficient Diels-Alder reaction. The as-prepared CMP exhibited a fused carbon backbone and a semiconductive characteristic with a band gap of 1.4 eV. When used as an organic electrode material in LIBs, the insoluble and robust fused structure caused such CMPs to exhibit remarkable cycling stability (a 96.1% capacity retention at 0.2 A g-1 after 200 cycles and a 94.8% capacity retention at 1 A g-1 after 1500 cycles), superior lithium-ion diffusion coefficient (5.30 × 10-11 cm2 s-1), and excellent rate capability (95.8 mAh g-1 at 1 A g-1). This study provided a novel synthetic method for fabricating quinone-enriched fused CMPs, which can be used as LIB cathode materials.

Inverted perovskite solar cells with enhanced lifetime and thermal stability enabled by a metallic tantalum disulfide buffer layer.

Perovskite solar cells (PSCs) have proved their potential for delivering high power conversion efficiencies (PCE) alongside low fabrication cost and high versatility. The stability and the PCE of PSCs can readily be improved by implementing engineering approaches that entail the incorporation of two-dimensional (2D) materials across the device's layered configuration. In this work, two-dimensional (2D) 6R-TaS2 flakes were exfoliated and incorporated as a buffer layer in inverted PSCs, enhancing the device's PCE, lifetime and thermal stability. A thin buffer layer of 6R-TaS2 flakes was formed on top of the electron transport layer to facilitate electron extraction, thus improving the overall device performance. The optimized devices reach a PCE of 18.45%, representing a 12% improvement compared to the reference cell. The lifetime stability measurements of the devices under ISOS-L2, ISOS-D1, ISOS-D1I and ISOS-D2I protocols revealed that the TaS2 buffer layer retards the intrinsic, thermally activated degradation processes of the PSCs. Notably, the devices retain more than the 80% of their initial PCE over 330 h under continuous 1 Sun illumination at 65 °C.

Topological defect-containing Fe/N co-doped mesoporous carbon nanosheets as novel electrocatalysts for the oxygen reduction reaction and Zn-air batteries.

Developing effective electrocatalysts for the oxygen reduction reaction is of great significance for clean and renewable energy technologies, such as metal-air batteries and fuel cells. Defect engineering is the central focus of this field because the overall catalytic performance crucially depends on highly active defects. For the ORR, topological defects have been proven to have a positive effect. However, because preparation and characterization of such defects are difficult, a basic understanding of the relationship between topological defects and catalytic performance remains elusive. In this study, topological defect-containing Fe/N co-doped mesoporous carbon nanosheets were synthesized using azulene-based sandwich-like polymer nanosheets as the precursor. As electrocatalysts, such porous carbon nanosheets exhibited promising ORR activity, methanol tolerance ability, and stability with a half-wave potential of 841 mV under alkaline conditions, which is superior to those of most of the reported porous carbons. As the air cathode for Zn-air batteries, the catalyst exhibited a peak power density of 153 mW cm-2 and a specific capacity of 628 mA h g-1,which were higher than those of a Pt/C-based Zn-air battery. Density functional theory calculation further proved the positive effect of topological defects on the oxygen reduction activity. These results indicate that bottom-up topological defect engineering could be a new and promising strategy for developing high-performance electrocatalysts.

Air-Processed Infrared-Annealed Printed Methylammonium-Free Perovskite Solar Cells and Modules Incorporating Potassium-Doped Graphene Oxide as an Interlayer.

The use of solution processes to fabricate perovskite solar cells (PSCs) represents a winning strategy to reduce capital expenditure, increase the throughput, and allow for process flexibility needed to adapt PVs to new applications. However, the typical fabrication process for PSC development to date is performed in an inert atmosphere (nitrogen), usually in a glovebox, hampering the industrial scale-up. In this work, we demonstrate, for the first time, the use of double-cation perovskite (forsaking the unstable methylammonium (MA) cation) processed in ambient air by employing potassium-doped graphene oxide (GO-K) as an interlayer, between the mesoporous TiO2 and the perovskite layer and using infrared annealing (IRA). We upscaled the device active area from 0.09 to 16 cm2 by blade coating the perovskite layer, exhibiting power conversion efficiencies (PCEs) of 18.3 and 16.10% for 0.1 and 16 cm2 active area devices, respectively. We demonstrated how the efficiency and stability of MA-free-based perovskite deposition in air have been improved by employing GO-K and IRA.

Metal Halide Perovskites for High-Energy Radiation Detection.

Metal halide perovskites (MHPs) have emerged as a frontrunner semiconductor technology for application in third generation photovoltaics while simultaneously making significant strides in other areas of optoelectronics. Photodetectors are one of the latest additions in an expanding list of applications of this fascinating family of materials. The extensive range of possible inorganic and hybrid perovskites coupled with their processing versatility and ability to convert external stimuli into easily measurable optical/electrical signals makes them an auspicious sensing element even for the high-energy domain of the electromagnetic spectrum. Key to this is the ability of MHPs to accommodate heavy elements while being able to form large, high-quality crystals and polycrystalline layers, making them one of the most promising emerging X-ray and γ-ray detector technologies. Here, the fundamental principles of high-energy radiation detection are reviewed with emphasis on recent progress in the emerging and fascinating field of metal halide perovskite-based X-ray and γ-ray detectors. The review starts with a discussion of the basic principles of high-energy radiation detection with focus on key performance metrics followed by a comprehensive summary of the recent progress in the field of perovskite-based detectors. The article concludes with a discussion of the remaining challenges and future perspectives.

An extensive case study on the dispersion parameters of HI-assisted reduced graphene oxide and its graphene oxide precursor.

The formation of highly concentrated and stable graphene derivatives dispersions remains a challenge towards their exploitation in various applications, including flexible optoelectronics, photovoltaics, 3D-printing, and biomedicine. Here, we demonstrate our extensive investigation on the dispersibility of graphene oxide (GO) and reduced graphene oxide (RGO) in 25 different solvents, without the use of any surfactant or stabilizer. Although there is a significant amount of work covering the general field, this is the first report on the dispersibility of: a) RGO prepared by a HI/AcOH assisted reduction process, the method which yields RGO of higher graphitization degree than the other well-known reductants met in the literature, b) both GO and RGO, explored in such a great range of solvents, with some of them not previously reported. In addition, through calculation of their Hansen Solubility Parameters (HSP), we confirmed their dispersibility behavior in each solvent, while we indirectly validated the most advanced graphitization degree of the studied RGO compared to other reported RGOs, since its HSPs exhibit the highest similarity with the respective ones of pure graphene. Finally, high concentrations of up to 189 µg mL-1 for GO and ~ 87.5 µg mL-1 for RGO were achieved, in deionized water and o-Dichlorobenzene respectively, followed by flakes size distribution and polydispersity indices estimation, through dynamic light scattering as a quality control of the effect of a solvent's nature on the dispersion behavior of these graphene-based materials.

Emphasizing the Operational Role of a Novel Graphene-Based Ink into High Performance Ternary Organic Solar Cells.

A novel solution-processed, graphene-based material was synthesized by treating graphene oxide (GO) with 2,5,7-trinitro-9-oxo-fluorenone-4-carboxylic acid (TNF-COOH) moieties, via simple synthetic routes. The yielded molecule N-[(carbamoyl-GO)ethyl]-N'-[(carbamoyl)-(2,5,7-trinitro-9-oxo-fluorene)] (GO-TNF) was thoroughly characterized and it was shown that it presents favorable highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy levels to function as a bridge component between the polymeric donor poly({4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl}{3-fluoro-2-[(2-ethylhexyl)carbonyl] thieno[3,4-b]thiophenediyl}) (PTB7) and the fullerene derivative acceptor [6,6]-phenyl-C71-butyric-acid-methylester (PC71BM). In this context, a GO-TNF based ink was prepared and directly incorporated within the binary photoactive layer, in different volume ratios (1%-3% ratio to the blend) for the effective realization of inverted ternary organic solar cells (OSCs) of the structure ITO/PFN/PTB7:GO-TNF:PC71BM/MoO3/Al. The addition of 2% v/v GO-TNF ink led to a champion power conversion efficiency (PCE) of 8.71% that was enhanced by ~13% as compared to the reference cell.

Limitations of a polymer-based hole transporting layer for application in planar inverted perovskite solar cells.

Planar inverted lead halide photovoltaics demonstrate remarkable photoconversion properties when employing poly(triarylamine) (PTAA) as a hole transporting layer. Herein, we elucidate the effect of ambient ultraviolet (UV) degradation on the structural and operational stability of the PTAA hole transporter through a series of rigorous optoelectrical characterization protocols. Due attention was given to the interplay between the polymer and perovskite absorber, both within the framework of a bilayer structure and fully assembled solar cells. The obtained results imply that UV degradation exerts a major influence on the structural integrity of PTAA, rather than on the interface with the perovskite light harvester. Moreover, UV exposure induced more adverse effects on tested samples than environmental humidity and oxygen, contributing more to the overall reduction of charge extraction properties of PTAA, as well as increased defect population upon prolonged UV exposure.

Updating the Role of Reduced Graphene Oxide Ink on Field Emission Devices in Synergy with Charge Transfer Materials.

Hydroiodic acid (HI)-treated reduced graphene oxide (rGO) ink/conductive polymeric composites are considered as promising cold cathodes in terms of high geometrical aspect ratio and low field emission (FE) threshold devices. In this study, four simple, cost-effective, solution-processed approaches for rGO-based field effect emitters were developed, optimized, and compared; rGO layers were coated on (a) n+ doped Si substrate, (b) n⁺-Si/P3HT:rGO, (c) n⁺-Si/PCDTBT:rGO, and (d) n⁺-Si/PCDTBT:PC71BM:rGO composites, respectively. The fabricated emitters were optimized by tailoring the concentration ratios of their preparation and field emission characteristics. In a critical composite ratio, FE performance was remarkably improved compared to the pristine Si, as well as n⁺-Si/rGO field emitter. In this context, the impact of various materials, such as polymers, fullerene derivatives, as well as different solvents on rGO function reinforcement and consequently on FE performance upon rGO-based composites preparation was investigated. The field emitter consisted of n⁺-Si/PCDTBT:PC71BM(80%):rGO(20%)/rGO displayed a field enhancement factor of ~2850, with remarkable stability over 20 h and low turn-on field in 0.6 V/µm. High-efficiency graphene-based FE devices realization paves the way towards low-cost, large-scale electron sources development. Finally, the contribution of this hierarchical, composite film morphology was evaluated and discussed.

Graphene-Based Inverted Planar Perovskite Solar Cells: Advancements, Fundamental Challenges, and Prospects.

Metal halide based perovskite solar cells (PSCs) are considered among the most promising photovoltaic technologies, and already present certified efficiencies that surpass 22 %. The high performance and low fabrication cost make this technology competitive with that of state-of-the-art thin-film photovoltaics. However, PSCs present some striking disadvantages that hinder their commercialization, including short operational lifetimes, high toxicity, and hysteresis effects, which lower both the performance and long-term stability of the devices. Herein, work conducted within the last two years is summarized with regard to addressing the challenges of low-temperature-processed planar inverted PSCs composed of graphene-based materials. In addition, critical challenges and the prospects of this field are discussed and some prospects for future research directions are proposed.

Solution Processed CH3NH3PbI3-xClx Perovskite Based Self-Powered Ozone Sensing Element Operated at Room Temperature.

Hybrid lead halide spin coated perovskite films have been successfully tested as portable, flexible, operated at room temperature, self-powered, and ultrasensitive ozone sensing elements. The electrical resistance of the hybrid lead mixed halide perovskite (CH3NH3PbI3-xClx) sensing element, was immediately decreased when exposed to an ozone (O3) environment and manage to recover its pristine electrical conductivity values within few seconds after the complete removal of ozone gas. The sensing measurements showed different response times at different gas concentrations, good repeatability, ultrahigh sensitivity and fast recovery time. To the best of our knowledge, this is the first time that a lead halide perovskite semiconductor material is demonstrating its sensing properties in an ozone environment. This work shows the potential of hybrid lead halide based perovskites as reliable sensing elements, serving the objectives of environmental control, with important socioeconomic impact.

Advanced Photonic Processes for Photovoltaic and Energy Storage Systems.

Solar-energy harvesting through photovoltaic (PV) conversion is the most promising technology for long-term renewable energy production. At the same time, significant progress has been made in the development of energy-storage (ES) systems, which are essential components within the cycle of energy generation, transmission, and usage. Toward commercial applications, the enhancement of the performance and competitiveness of PV and ES systems requires the adoption of precise, but simple and low-cost manufacturing solutions, compatible with large-scale and high-throughput production lines. Photonic processes enable cost-efficient, noncontact, highly precise, and selective engineering of materials via photothermal, photochemical, or photophysical routes. Laser-based processes, in particular, provide access to a plethora of processing parameters that can be tuned with a remarkably high degree of precision to enable innovative processing routes that cannot be attained by conventional approaches. The focus here is on the application of advanced light-driven approaches for the fabrication, as well as the synthesis, of materials and components relevant to PV and ES systems. Besides presenting recent advances on recent achievements, the existing limitations are outlined and future possibilities and emerging prospects discussed.