Mesoporous Networks of N-Vinylpyrrolidone with (di)Methacrylates as Precursors of Ecological Molecular Imprinted Polymers.

Mesoporous polymer networks were prepared via the cross-linking radical copolymerization of non-toxic hydrophilic N-vinylpyrrolidone (VP) with triethylene glycol dimethacrylate (TEGDM) and poly(ethylene glycol) methyl ester methacrylate (PEGMMA) in bulk, using appropriate soluble and thermodynamically compatible macromolecular additives with a branched structure as porogens. The branched copolymers of various monomer compositions were obtained by radical copolymerization in toluene, controlled by 1-decanethiol, and these materials were characterized by a wide set of physical chemical methods. The specific surface areas and surface morphology of the polymer networks were determined by nitrogen low-temperature adsorption or Rose Bengal (RB) sorption, depending on the copolymer compositions and scanning electron microscopy. The electrochemical properties of RB before and after its encapsulation into a branched VP copolymer were studied on a glassy carbon electrode and the interaction between these substances was observed. Quantum chemical modeling of RB-VP or RB-copolymer complexes has been carried out and sufficiently strong hydrogen bonds were found in these systems. The experimental and modeling data demonstrate the high potency of such mesoporous polymer networks as precursors of molecularly imprinted polymers for the recognition of fluorescent dyes as nanomarkers for biomedical practice.

Features and Consequences of Isopropanol Burning off PTFE-rGO Aerogels.

An improved procedure for the preparation of aerogel granules of polytetrafluoroethylene-graphene oxide (PTFE-GO) with a composition of 50:50 (in wt %) and a specific density of 35 ± 2 mg/cm3 is described. The technique practically excludes the granule cracking. The specific density of the pellets after reduction using hydrazine vapor and annealing at 370 °C decreased to 29 ± 2 mg/cm3. The PTFE-reduced GO (rGO) pellets obtained were tested as a recyclable sorbent for isopropyl alcohol (IPA) in sorption/combustion cycles. It has been shown that the aerogel sorption capacity for IPA increases from 35.6 to 39.3 g/g as a result of alcohol burning off. During the combustion of IPA, the temperature of an individual pellet can exceed 300 °C. When several contingent pellets are burned, the temperature of their heating increases. The fine-pored structure of the near-surface layer of the granule is destroyed during the alcohol burning, the internal structure with larger pores is exposed, and the relative proportion of PTFE on the surface of the granules decreases. It was also shown that the specific surface area of PTFE-rGO increases from 26 to 49 m2/g during cycling.

Temperature Dynamics of MAPbI3 and PbI2 Photolysis: Revealing the Interplay between Light and Heat, Two Enemies of Perovskite Photovoltaics.

Regardless of the impressive photovoltaic performances demonstrated for lead halide perovskite solar cells, their practical implementation is severely impeded by the low device stability. Complex lead halides are sensitive to both light and heat, which are unavoidable under realistic solar cell operational conditions. Suppressing these intrinsic degradation pathways requires a thorough understanding of their mechanistic aspects. Herein, we explored the temperature effects in the light-induced decomposition of MAPbI3 and PbI2 thin films under anoxic conditions. The analysis of the aging kinetics revealed that MAPbI3 photolysis and PbI2 photolysis have quite high effective activation energies of ∼85 and ∼106 kJ mol-1, respectively, so decreasing the temperature from 55 to 30 °C can extend the perovskite lifetime by factors of >10-100. These findings suggest that controlling the temperature of the perovskite solar panels might allow the long operational lifetimes (>20 years) required for the practical implementation of this promising technology.

Partial Substitution of Pb2+ in CsPbI3 as an Efficient Strategy To Design Fairly Stable All-Inorganic Perovskite Formulations.

All-inorganic lead halide perovskites, for example, CsPbI3, are becoming more attractive for applications as light absorbers in perovskite solar cells because of higher thermal and photochemical stability as compared to their hybrid analogues. However, a specific drawback of the CsPbI3 absorber consists of the rapid phase transition from black to yellow nonphotoactive phase at low temperatures (e.g., <100 °C), which is accelerated under exposure to light. Herein, an experimental screening of an unprecedently large series (>30) of metal cations in a wide range of concentration has allowed us to establish a set of Pb2+ substitutes, facilitating the crystallization of the photoactive black CsPbI3 phase at low temperatures. Importantly, the appropriate Pb2+ substitution with Ca2+, Sr2+, Ce3+, Nd3+, Gd3+, Tb3+, Dy2+, Er3+, Yb2+, Lu3+, and Pt2+ cations has led to a spectacular enhancement of the film stability under realistic solar cell operation conditions (∼1 sun equivalent light exposure, 50 °C). Optoelectronic, structural, and morphological effects of partial Pb2+ substitution were investigated, providing a deeper insight into the processes underlying the stabilization of the CsPbI3 films. Several CsPb1-xMxI∼3 systems were evaluated as absorber materials in perovskite solar cells, demonstrating encouraging light power conversion efficiency of 11.4% in preliminary experiments. The obtained results feature the potential of designing efficient and stable all-inorganic perovskite solar cells using novel absorber materials rationally designed via compositional engineering.

Reduced Graphene Oxide Aerogel inside Melamine Sponge as an Electrocatalyst for the Oxygen Reduction Reaction.

A graphene oxide aerogel (GOA) was formed inside a melamine sponge (MS) framework. After reduction with hydrazine at 60 °C, the electrical conductive nitrogen-enriched rGOA-MS composite material with a specific density of 20.1 mg/cm3 was used to fabricate an electrode, which proved to be a promising electrocatalyst for the oxygen reduction reaction. The rGOA-MS composite material was characterized by elemental analysis, scanning electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. It was found that nitrogen in the material is presented by different types with the maximum concentration of pyrrole-like nitrogen. By using Raman scattering it was established that the rGOA component of the material is graphene-like carbon with an average size of the sp2-domains of 5.7 nm. This explains a quite high conductivity of the composite obtained.

Solubilizing Side Chain Engineering: Efficient Strategy to Improve the Photovoltaic Performance of Novel Benzodithiophene-Based (X-DADAD)n Conjugated Polymers.

Conjugated polymers represent a promising family of semiconductor materials for thin-film organic solar cells (OSCs). An efficient approach to improve the photovoltaic performance of conjugated polymers is engineering the side chains attached to the polymer backbone. This work reports the impact of different alkyl substituents on the optoelectronic properties, charge carrier mobilities, thin film morphology, and photovoltaic performance of novel (X-DADAD)n conjugated polymers incorporating benzo[1,2-b:4,5-b']dithiophene moieties. It has been shown that loading conjugated polymers with appropriate alkyl side chains results in a spectacular performance improvement from 6.8% to 9% in OCSs using a model fullerene acceptor [6,6]-phenyl-C71 -butyric acid methyl ester. The obtained results feature side-chain engineering as a facile and efficient strategy for designing high-performance conjugated polymers for organic photovoltaics.

Efficient and Stable MAPbI3-Based Perovskite Solar Cells Using Polyvinylcarbazole Passivation.

Hybrid perovskite solar cells attract a great deal of attention due to the feasibility of their low-cost production and their demonstration of impressive power conversion efficiencies (PCEs) exceeding 25%. However, the insufficient intrinsic stability of lead halides under light soaking and thermal stress impedes practical implementation of this technology. Herein, we show that the photothermal aging of a widely used perovskite light absorber such as MAPbI3 can be suppressed significantly by using polyvinylcarbazole (PVC) as a stabilizing agent. By applying a few complementary methods, we reveal that the PVC additive leads to passivation of defects in the absorber material. Introducing an optimal content of PVC into MAPbI3 delivers a PCE of 18.7% in combination with a significantly improved solar cell operational lifetime: devices retained ∼70% of the initial efficiency after light soaking for 1500 h, whereas the control samples without PVC degraded almost completely under the same conditions.

Preparation and Characterization of a Flexible rGO-PTFE Film for a Supercapacitor Current Collector.

A mixture of water suspensions of graphene oxide (GO) and polytetrafluoroethylene (PTFE) was used to make the films GO-PTFE (50:50). They became conductive (2.0-2.8 S/cm) while maintaining flexibility after reduction with hydrazine and subsequent annealing at 370 °C. The structure and morphology of the reduced films (rGO-PTFE) are examined in detail by means of a number of techniques such as scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy, Raman, and contact angle wetting. The results of the films tested as current collectors in a metal-free supercapacitor with electrodes from microwave exfoliated GO and an acid (1 M H2SO4) electrolyte are presented.

Light or Heat: What Is Killing Lead Halide Perovskites under Solar Cell Operation Conditions?

We report the first systematic assessment of intrinsic photothermal stability of a large panel of complex lead halides APbX3 incorporating different univalent cations (A = CH3NH3+, [NH2CHNH2]+, Cs+) and halogen anions (X = Br, I) using a series of analytical techniques such as UV-vis and X-ray photoelectron spectroscopy, X-ray diffraction, EDX analysis, atomic force and scanning electron microscopy, ESR spectroscopy, and mass spectrometry. We show that heat stress and light soaking induce a severe degradation of perovskite films even in the absence of oxygen and moisture. The stability of complex lead halides increases in the order MAPbBr3 < MAPbI3 < FAPbI3 < FAPbBr3 < CsPbI3 < CsPbBr3, thus featuring all-inorganic perovskites as the most promising absorbers for stable perovskite solar cells. An important correlation was found between the stability of the complex lead halides and the volatility of univalent cation halides incorporated in their structure. The established relationship provides useful guidelines for designing new complex metal halides with immensely improved stability.

Novel Superhydrophobic Aerogel on the Base of Polytetrafluoroethylene.

Polytetrafluoroethylene-based aerogel was synthesized for the first time. Graphene oxide was used as a binder. After reduction with hydrazine and annealing at 370 °C, the aerogel with a density of 29 ± 2 mg/cm3 became superhydrophobic. The aerogel was characterized by IR spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy. The sorption capacity of the aerogel for seven solvents and its sorption recyclability for hexane were measured.

Exploring the Photovoltaic Performance of All-Inorganic Ag2PbI4/PbI2 Blends.

We present an all-inorganic photoactive material composed of Ag2PbI4 and PbI2, which shows unexpectedly good photovoltaic performance in planar junction solar cells delivering external quantum efficiencies of ∼60% and light power conversion efficiencies of ∼3.9%. The revealed characteristics are among the best reported to date for metal halides with nonperovskite crystal structure. Most importantly, the obtained results suggest a possibility of reaching high photovoltaic efficiencies for binary and, probably, also ternary blends of different inorganic semiconductor materials. This approach, resembling the bulk heterojunction concept guiding the development of organic photovoltaics for two decades, opens wide opportunities for rational design of novel inorganic and hybrid materials for efficient and sustainable photovoltaic technologies.

Probing the Intrinsic Thermal and Photochemical Stability of Hybrid and Inorganic Lead Halide Perovskites.

We report a careful and systematic study of thermal and photochemical degradation of a series of complex haloplumbates APbX3 (X = I, Br) with hybrid organic (A+ = CH3NH3) and inorganic (A+ = Cs+) cations under anoxic conditions (i.e., without exposure to oxygen and moisture by testing in an inert glovebox environment). We show that the most common hybrid materials (e.g., MAPbI3) are intrinsically unstable with respect to the heat- and light-induced stress and, therefore, can hardly sustain the real solar cell operation conditions. On the contrary, the cesium-based all-inorganic complex lead halides revealed far superior stability and, therefore, provide an impetus for creation of highly efficient and stable perovskite solar cells that can potentially achieve pragmatic operational benchmarks.

Highly Efficient All-Inorganic Planar Heterojunction Perovskite Solar Cells Produced by Thermal Coevaporation of CsI and PbI2.

We report here all inorganic CsPbI3 planar junction perovskite solar cells fabricated by thermal coevaporation of CsI and PbI2 precursors. The best devices delivered power conversion efficiency (PCE) of 9.3 to 10.5%, thus coming close to the reference MAPbI3-based devices (PCE ≈ 12%). These results emphasize that all inorganic lead halide perovskites can successfully compete in terms of photovoltaic performance with the most widely used hybrid materials such as MAPbI3.

Exploring the Effects of the Pb2+ Substitution in MAPbI3 on the Photovoltaic Performance of the Hybrid Perovskite Solar Cells.

Here we report a systematic study of the Pb2+ substitution in the hybrid iodoplumbate MAPbI3 with a series of elements affecting optoelectronic, structural, and morphological properties of the system. It has been shown that even partial replacement of lead with Cd2+, Zn2+, Fe2+, Ni2+, Co2+, In3+, Bi3+, Sn4+, and Ti4+ results in a significant deterioration of the photovoltaic characteristics. On the contrary, Hg-containing hybrid MAPb1-xHgxI3 salts demonstrated a considerably improved solar cell performance at optimal mercury loading. This result opens up additional dimension in the compositional engineering of the complex lead halides for designing novel photoactive materials with advanced optoelectronic and photovoltaic properties.

The chemical origin of the p-type and n-type doping effects in the hybrid methylammonium-lead iodide (MAPbI3) perovskite solar cells.

In the present Communication we discuss a field-induced and photoinduced self-doping chemistry resulting in the formation of the positively and negatively charged vacancies in the MAPbI3 perovskite films. These vacancies induce p-type and n-type doping of the perovskite absorber leading to the realization of the p-i-n device operation mechanism.

Towards understanding the behavior of indigo thin films in organic field-effect transistors: a template effect of the aliphatic hydrocarbon dielectric on the crystal structure and electrical performance of the semiconductor.

Here we report a systematic investigation of indigo thin films grown on different dielectric underlayers. It has been revealed that aliphatic hydrocarbon chains serve as templates inducing the formation of a new crystal modification of indigo which possesses advanced charge transport properties and affords a dramatic improvement in the electrical performance of organic field-effect transistors.

Material structure-composite morphology-photovoltaic performance relationship for organic bulk heterojunction solar cells.

Conjugated PPV-PPE copolymer has been investigated in organic solar cells in combination with twelve different fullerene derivatives. It was shown that the length of solubilizing alkyl chains in the fullerene derivative structures correlates well with the performance of photovoltaic cells.