Perovskite solar cells (PSCs) with efficiencies greater than 20% have been realized only with expensive organic hole-transporting materials. We demonstrate PSCs that achieve stabilized efficiencies exceeding 20% with copper(I) thiocyanate (CuSCN) as the hole extraction layer. A fast solvent removal method enabled the creation of compact, highly conformal CuSCN layers that facilitate rapid carrier extraction and collection. The PSCs showed high thermal stability under long-term heating, although their operational stability was poor. This instability originated from potential-induced degradation of the CuSCN/Au contact. The addition of a conductive reduced graphene oxide spacer layer between CuSCN and gold allowed PSCs to retain >95% of their initial efficiency after aging at a maximum power point for 1000 hours under full solar intensity at 60°C. Under both continuous full-sun illumination and thermal stress, CuSCN-based devices surpassed the stability of spiro-OMeTAD–based PSCs.

https://science.sciencemag.org/content/sci/early/2017/09/27/science.aam5655.full.pdf

Perovskite solar cells with CuSCN hole extraction layers yield stabilized efficiencies greater than 20

Transition metal carbides and nitrides (MXenes), a family of two-dimensional (2D) inorganic compounds, are materials composed of a few atomic layers of transition metal carbides, nitrides, or carbonitrides. Ti3C2, the first 2D layered MXene, was isolated in 2011. This material, which is a layered bulk material analogous to graphite, was derived from its 3D phase, Ti3AlC2 MAX. Since then, material scientists have either determined or predicted the stable phases of >200 different MXenes based on combinations of various transition metals such as Ti, Mo, V, Cr, and their alloys with C and N. Extensive experimental and theoretical studies have shown their exciting potential for energy conversion and electrochemical storage. To this end, we comprehensively summarize the current advances in MXene research. We begin by reviewing the structure types and morphologies and their fabrication routes. The review then discusses the mechanical, electrical, optical, and electrochemical properties of MXenes. The focus then turns to their exciting potential in energy storage and conversion. Energy storage applications include electrodes in rechargeable lithium- and sodium-ion batteries, lithium-sulfur batteries, and supercapacitors. In terms of energy conversion, photocatalytic fuel production, such as hydrogen evolution from water splitting, and carbon dioxide reduction are presented. The potential of MXenes for the photocatalytic degradation of organic pollutants in water, such as dye waste, is also addressed, along with their promise as catalysts for ammonium synthesis from nitrogen. Finally, their application potential is summarized.

Applications of 2D MXenes in energy conversion and storage systems

Lightweight, ultrathin, and flexible electromagnetic interference (EMI) shielding materials are needed to protect electronic circuits and portable telecommunication devices and to eliminate cross-talk between devices and device components. Here, we show that a two-dimensional (2D) transition metal carbonitride, Ti3CNTx MXene, with a moderate electrical conductivity, provides a higher shielding effectiveness compared with more conductive Ti3C2Tx or metal foils of the same thickness. This exceptional shielding performance of Ti3CNTx was achieved by thermal annealing and is attributed to an anomalously high absorption of electromagnetic waves in its layered, metamaterial-like structure. These results provide guidance for designing advanced EMI shielding materials but also highlight the need for exploring fundamental mechanisms behind interaction of electromagnetic waves with 2D materials.

https://science.sciencemag.org/content/sci/369/6502/446.full.pdf

Anomalous absorption of electromagnetic waves by 2D transition metal carbonitride Ti3CNTx (MXene)

The COVID-19 outbreak has fueled a global demand for effective diagnosis and treatment as well as mitigation of the spread of infection, all through large-scale approaches such as specific alternative antiviral methods and classical disinfection protocols. Based on an abundance of engineered materials identifiable by their useful physicochemical properties through versatile chemical functionalization, nanotechnology offers a number of approaches to cope with this emergency. Here, through a multidisciplinary Perspective encompassing diverse fields such as virology, biology, medicine, engineering, chemistry, materials science, and computational science, we outline how nanotechnology-based strategies can support the fight against COVID-19, as well as infectious diseases in general, including future pandemics. Considering what we know so far about the life cycle of the virus, we envision key steps where nanotechnology could counter the disease. First, nanoparticles (NPs) can offer alternative methods to classical disinfection protocols used in healthcare settings, thanks to their intrinsic antipathogenic properties and/or their ability to inactivate viruses, bacteria, fungi, or yeasts either photothermally or via photocatalysis-induced reactive oxygen species (ROS) generation. Nanotechnology tools to inactivate SARS-CoV-2 in patients could also be explored. In this case, nanomaterials could be used to deliver drugs to the pulmonary system to inhibit interaction between angiotensin-converting enzyme 2 (ACE2) receptors and viral S protein. Moreover, the concept of "nanoimmunity by design" can help us to design materials for immune modulation, either stimulating or suppressing the immune response, which would find applications in the context of vaccine development for SARS-CoV-2 or in counteracting the cytokine storm, respectively. In addition to disease prevention and therapeutic potential, nanotechnology has important roles in diagnostics, with potential to support the development of simple, fast, and cost-effective nanotechnology-based assays to monitor the presence of SARS-CoV-2 and related biomarkers. In summary, nanotechnology is critical in counteracting COVID-19 and will be vital when preparing for future pandemics.

Toward Nanotechnology-Enabled Approaches against the COVID-19 Pandemic.

Traditional ways of producing drinking water from groundwater, water recycling and water conservation are not sufficient. Seawater desalination would close the gap but the main technology used is thermally driven multi-flash distillation, which is energy consuming and not sustainable. Stacking two-dimensional (2D) nanomaterials into lamellar membranes is a promising technique in the pursuit of both high selectivity and permeance in water desalination. However, 2D membranes tend to swell in water, and increasing their stability in aqueous solution is still challenging. Here, we report non-swelling, MXene membranes prepared by the intercalation of Al3+ ions. Swelling is prevented by strong interactions between Al3+ and oxygen functional groups terminating at the MXene surface. These membranes show excellent non-swelling stability in aqueous solutions up to 400 h and possess high rejection of NaCl (~89.5–99.6%) with fast water fluxes (~1.1–8.5 l m−2 h−1). Such membranes can be easily fabricated by simple filtration and ion-intercalating methods, which holds promise for their scalability. Two-dimensional lamellar membranes for water purification are promising but suffer from swelling that reduces their ion sieving performance in water. This study reports easy-to-fabricate, non-swelling MXene membranes prepared by the intercalation of Al3+ ions that could be scalable.

Effective ion sieving with Ti 3 C 2 T x MXene membranes for production of drinking water from seawater

Low flux and fouling are critical issues in membrane based separation processes. Here we report a two-dimensional (2D) MXene (Ti3C2Tx) modified with Ag nanoparticles (Ag@MXene) as a promising alternative for ultrafast water purification membrane applications. The novel Ag@MXene composite membrane with variable AgNP loadings (between 0–35%) was produced by self-reduction of silver nitrate on the surface of MXene sheets in solution, where the MXene acted simultaneously as a membrane forming material and a reducing agent. The most suitable membrane, 21% Ag@MXene with 470 nm thickness and 2.1 nm average pore size, exhibited an outstanding water flux (∼420 L m−2 h−1 bar−1) compared to the pristine MXene membrane (∼118 L m−2 h−1 bar−1) under the same experimental conditions. The 21% Ag@MXene membrane demonstrated high rejection efficiency for organic molecules with excellent flux recovery. Moreover, the 21% Ag@MXene composite membrane demonstrated more than 99% E. coli growth inhibition, while the MXene membrane exhibited only ∼60% bacteria growth inhibition compared to the control hydrophilic polyvinylidene difluoride (PVDF) based membrane. Furthermore, the 21% Ag@MXene membrane achieved favorable rejection to organic foulants like bovine serum albumin (BSA) and methyl green (MG) in comparison to other reported membranes. This combination of controlled permeability and bactericidal properties makes Ag@MXene layered nanosheets attractive candidates towards the development of nanofiltration membranes for water purification and biomedical applications.

Ultrahigh-flux and fouling-resistant membranes based on layered silver/MXene (Ti3C2Tx) nanosheets

In this Letter we show that the mixed perovskite in the form of (FAPbI3)0.85(MAPbBr3)0.15 in combination with CuNCS as p-type hole conductor leads to over 16% power conversion efficiency (PCE) under full sun illumination and yields a remarkable monochromatic incident photon-to-electron conversion efficiency of 85%. The devices displayed a short-circuit current density (Jsc) of 21.8 mA/cm2, open-circuit voltage (Voc) of 1100 mV, fill factor (FF) of 0.69, and a PCE of 16.6%. Under similar conditions, the device without CuSCN shows a PCE of 9.5%, with a significant decrease in the Jsc (from 21.8 mA/cm2 to 15.64 mA/cm2) and Voc (from 1100 mV to 900 mV). The high Jsc with CuSCN is mainly due to the effective charge transfer between perovskite and CuSCN, followed by the fast hole transport through CuSCN to the Au. In comparison, the spiro-OMeTAD reference cells showed efficiencies up to 19.65%. Different from most organic hole-transporting materials is the transparency and high hole mobility of CuSCN, which rep...

Copper Thiocyanate Inorganic Hole-Transporting Material for High-Efficiency Perovskite Solar Cells

We report stable perovskite solar cells having 3D/2D perovskite absorber layers and CuSCN as an inorganic hole transporting material (HTM). (Phenylethyl)ammonium (PEA) and [(4-fluorophenyl)ethyl]am...

CuSCN as Hole Transport Material with 3D/2D Perovskite Solar Cells

Recently, extensive R&D has been conducted, both by industry and academia, to significantly raise the conversion efficiency of commercial photovoltaic (PV) modules. The installation of PV systems aimed at optimizing solar energy yield is primarily dictated by its geographic location and installation design to maximize solar exposure. However, even when these characteristics have been addressed appropriately, there are other factors that adversely affect the performance of PV systems, namely the temperature-induced voltage decrease leading to a PV power loss, and the dust accumulation (soiling). The latter is the lesser acknowledged factor that significantly influences the performance of PV installations especially in the Middle East region. In this paper we report on the investigation of the structural and physical properties of the desert-dust particles in the State of Qatar. The dust particles were collected directly from the PV panels installed in desert environment and characterized by different techniques, including scanning electron, optical and atomic force microscopies, X-ray diffraction, energy-dispersive, UV-Vis, micro-Raman and Fourier transform infrared spectroscopy. The vibrating sample magnetometry analyses were also conducted to study the magnetic properties of the dust particles. The influence of the dust accumulation on the PV panel performance was also presented and discussed.

/pdf/structural-and-physical-properties-of-the-dust-particles-in-58pdouwrmy.pdf

Vinod E. Madhavan

Papers

Ultrahigh-flux and fouling-resistant membranes based on layered silver/MXene (Ti3C2Tx) nanosheets

Copper Thiocyanate Inorganic Hole-Transporting Material for High-Efficiency Perovskite Solar Cells

CuSCN as Hole Transport Material with 3D/2D Perovskite Solar Cells

Structural and physical properties of the dust particles in Qatar and their influence on the PV panel performance.

Sulfurization and annealing effects on thermally evaporated CZTS films