Protic Amine Carboxylic Acid Ionic Liquids Additives Regulate α-FAPbI3 Phase Transition for High Efficiency Perovskite Solar Cells.

The α-phase formamidinium lead tri-iodide (α-FAPbI3 ) has become the most promising photovoltaic absorber for perovskite solar cells (PSCs) due to its outstanding semiconductor properties and astonishing high efficiency. However, the incomplete crystallization and phase transition of α-FAPbI3 substantially undermine the performance and stability of PSCs. In this work, a series of the protic amine carboxylic acid ion liquids are introduced as the precursor additives to efficiently regulate the crystal growth and phase transition processes of α-FAPbI3 . The MA2 Pb3 I8 ·2DMSO phase is inhibited in annealing process, which remarkably optimizes the phase transition process of α-FAPbI3 . It is noted that the functional groups of carboxyl and ammonium passivate the undercoordinated lead ions, halide vacancies, and organic vacancies, eliminating the deleterious nonradiative recombination. Consequently, the small-area devices incorporated with 2% methylammonium butyrate (MAB) and 1.5% n-butylammonium formate (BAFa) in perovskite show champion efficiencies of 25.10% and 24.52%, respectively. Furthermore, the large-area modules (5 cm × 5 cm) achieve PCEs of 21.26% and 19.27% for MAB and BAFa additives, indicating the great potential for commercializing large-area PSCs.

Low-Cost Hydroxyacid Potassium Synergists as an Efficient In Situ Defect Passivator for High Performance Tin-Oxide-Based Perovskite Solar Cells.

Perovskite solar cells (PSCs) based on SnO2 electron transport layers have attracted extensive research due to their compelling photovoltaic performance. Herein, we presented an in situ passivation of SnO2 with low-cost hydroxyacid potassium synergist during deposition to optimize the interface carrier extraction and transport for high power conversion efficiency (PCE) and stabilities of PSCs. The orbital overlap of the carboxyl oxygen with the Sn atom alongwith the homogenous nano-particle deposition effectively suppresses the interfacial defects and releases the internal residual strains in the perovskite. Accordingly, a PCE of 24.91 % with a fill factor (FF) up to 0.852 is obtained for in situ passivated devices, which is one of the highest values for SnO2 -based PSCs. Moreover, the unencapsulated device maintained 80 % of its initial PCE at 80 °C over 600 h, 100 % PCE at ambient conditions for 1300 h, and 98 % after one week maximum power point tracking (MPPT) under continuous AM1.5G illumination.

3D Nitrogen-Doped Graphene Encapsulated Metallic Nickel-Iron Alloy Nanoparticles for Efficient Bifunctional Oxygen Electrocatalysis.

Invited for the cover of this issue is Liqiang Mai and co-workers at Wuhan University of Technology. The image depicts Ni3 Fe alloy nanoparticles encapsulated in N-doped graphene as an efficient bifunctional oxygen electrocatalyst toward rechargeable Zn-air batteries, which is expected to drive the electric vehicle. Read the full text of the article at 10.1002/chem.201904722.

3D Nitrogen-Doped Graphene Encapsulated Metallic Nickel-Iron Alloy Nanoparticles for Efficient Bifunctional Oxygen Electrocatalysis.

It is extremely desirable to explore high-efficient, affordable and robust oxygen electrocatalysts toward rechargeable Zn-air batteries (ZABs). A 3D porous nitrogen-doped graphene encapsulated metallic Ni3 Fe alloy nanoparticles aerogel (Ni3 Fe-GA1 ) was constructed through a facile hydrothermal assembly and calcination process. Benefiting from 3D porous configuration with great accessibility, high electrical conductivity, abundant active sites, optimal nitrogen content and strong electronic interactions at the Ni3 Fe/N-doped graphene heterointerface, the obtained aerogel showed outstanding catalytic performance toward the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Specifically, it exhibited an overpotential of 239 mV to attain 10 mA cm-2 for OER, simultaneously providing a positive onset potential of 0.93 V within a half-wave potential of 0.8 V for ORR. Accordingly, when employed in the aqueous ZABs, Ni3 Fe-GA1 achieved higher power density and superior reversibility than Pt/C-IrO2 catalyst, making it a potential candidate for rechargeable ZABs.

Interface modification effect on the performance of CsxFA1-xPbIyBr3-y perovskite solar cells fabricated by evaporation/spray-coating method.

In this study, high quality CsxFA1-xPbIyBr3-y perovskite thin films were successfully fabricated by an evaporation/spray-coating hybrid deposition method. In this method, CsI and PbI2 were first deposited via thermal evaporation, and then FAI/FABr mixed solution was sprayed on the CsI/PbI2 substrate to form the CsxFA1-xPbIyBr3-y film. As confirmed by x-ray diffraction, scanning electron microscopy, and atomic force microscopy, a perovskite film with full surface coverage and small surface roughness was obtained. Then, the effect of interface modification materials on the performance of perovskite solar cells (PSCs) was investigated: the devices with the [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) interlayer incorporated via vacuum evaporation deposition between SnO2 and perovskite showed remarkably higher performance than those with the C60 interlayer, which was attributed to enhanced charge extraction and reduced recombination at the SnO2/PCBM/perovskite interface. As a result, a high power conversion efficiency (PCE) of 18.21% was obtained for the 0.16 cm2 device. To the best of our knowledge, it is the highest efficiency of CsxFA1-xPbIyBr3-y based PSCs fabricated by the spray technique. Furthermore, we fabricated mini-modules with the size of 5 × 5 cm2 and achieved a PCE of 14.7%.

Sequentially Reinforced Additive Coating for Transparent and Durable Superhydrophobic Glass.

Now that there are various routes to prepare superhydrophobic surfaces for self-cleaning, anti-icing, liquid collecting, etc., attentions are moving toward low-cost upscaling of routes and increasing the reliability for actual applications. However, the required micro-nano structures for superhydrophobicity are light scattering and very vulnerable to abrasion. This intrinsically conflicts with the transparency and durability of superhydrophobic glass, which are the major barriers for its commercialization. In this study, we present a novel sequentially reinforced additive coating (SRAC) process to realize robust and transparent micro-nano structured film with tough intergranular sintering. A benign aqueous-based ink with poly(furfuryl alcohol) (PFA) and silica species is carefully designed and sprayed on glass to enable self-phase separation and morphology construction. The coatings reach the static contact angle (SCA) for water over 166° and withstand a 6H pencil scratching, the cross-cut test, and sand abrasion. Moreover, we also performed a 90 day outdoor performance test and the glass maintained superhydrophobicity with an SCA of 154°. These results provide a low-cost waterborne ink formula, and the high throughput and upscalable SRAC process could be a convenient technology for the fabrication of large area, robust superhydrophobic coatings.

Photovoltaic performance and the energy landscape of CH3NH3PbI3.

Photovoltaic cells with absorbing layers of certain perovskites have power conversion efficiencies up to 20%. Among these materials, CH3NH3PbI3 is widely used. Here we use density-functional theory to calculate the energies and rotational energy barriers of a methylammonium ion in the α or ß phase of CH3NH3PbI3 with differently oriented neighbouring methylammonium ions. Our results suggest the methylammonium ions in CH3NH3PbI3 prefer to rotate collectively, and to be parallel to their neighbours. Changes in polarization on rotation of methylammonium ions are two to three times larger than those on relaxation of the lead ion from the centre of its coordination shell. The preferences for parallel configuration and concerted rotation, with the polarisation changes, are consistent with ferroelectricity in the material, and indicate that this polarisation is governed by methylammonium orientational correlations. We show that the field due to this polarisation is strong enough to screen the field hindering charge transport, and find this screening field in agreement with experiment. We examine two possible mechanisms for the effect of methylammonium ion rotation on photovoltaic performance. One is that rearrangement of methylammoniums promotes the creation and transport of charge carriers. Some effective masses change greatly, but changes in band structure with methylammonium rotation are not large enough to explain current-voltage hysteresis behaviour. The second possible mechanism is that polarization screens the hindering electric field, which arises from charge accumulation in the transport layers. Polarization changes on methylammonium rotation favour this second mechanism, suggesting that collective reorientation of methylammonium ions in the bulk crystal are in significant part responsible for the hysteresis and power conversion characteristics of CH3NH3PbI3 photovoltaic cells.

Controlling interfacial recombination in aqueous dye-sensitized solar cells by octadecyltrichlorosilane surface treatment.

A general and convenient strategy is proposed for enhancing photovoltaic performance of aqueous dye-sensitized solar cells (DSCs) through the surface modification of titania using an organic alkyl silane. Introduction of octadecyltrichlorosilane on the surface of dyed titania photoanode as an organic barrier layer leads to the efficient suppression of electron recombination with oxidized cobalt species by restricting access of the cobalt redox couple to the titania surface. The champion ODTS-treated aqueous DSCs (0.25 mM ODTS in hexane for 5 min) exhibit a V(oc) of 821±4 mV and J(sc) of 10.17±0.21 mA cm(-2), yielding a record PCE of 5.64±0.10%. This surface treatment thus serves as a promising post-dye strategy for improving the photovoltaic performance of other aqueous DSCs.

A fast deposition-crystallization procedure for highly efficient lead iodide perovskite thin-film solar cells.

Thin-film photovoltaics based on alkylammonium lead iodide perovskite light absorbers have recently emerged as a promising low-cost solar energy harvesting technology. To date, the perovskite layer in these efficient solar cells has generally been fabricated by either vapor deposition or a two-step sequential deposition process. We report that flat, uniform thin films of this material can be deposited by a one-step, solvent-induced, fast crystallization method involving spin-coating of a DMF solution of CH3NH3PbI3 followed immediately by exposure to chlorobenzene to induce crystallization. Analysis of the devices and films revealed that the perovskite films consist of large crystalline grains with sizes up to microns. Planar heterojunction solar cells constructed with these solution-processed thin films yielded an average power conversion efficiency of 13.9±0.7% and a steady state efficiency of 13% under standard AM 1.5 conditions.

Construction and regulation of high active sites in montmorillonite composite catalyst for the removal of ofloxacin via persulfate activation.

In this study, ionic liquids (ILs) were used as organic modifiers by introducing montmorillonite nanolayers containing potential C and N active sites between the montmorillonite nanolayers. Organically modified montmorillonite (ILs-Mt-p) was further prepared by high-temperature pyrolysis under N2 and used for the removal of ofloxacin (OFL) by activated peroxymonosulfate (PMS). Combined with XPS and other characterization analyses, it was found that the catalyst materials prepared from different organic modifiers had similar surface functional groups and graphitized structures, but contained differences in the types and numbers of C and N active sites. The catalyst (3CPC-Mt-p) obtained after pyrolysis of montmorillonite modified with cetylpyridinium chloride (CPC) had optimal catalytic performance, in which graphitic C, graphitic N, and carbonyl group (C[bond, double bond]O) could synergistically promote the activation of PMS by electron transfer, and 77.3 % of OFL could be removed within 60 min. The effects of OFL concentration, initial pH, and anions on the effects of OFL removal by the 3CPC-Mt-p/PMS system were further investigated. Satisfactory degradation results were obtained over a wide pH range. Cl- promoted the system to degrade OFL, while the presence of SO42-, H2PO4- and HA showed some inhibition, but overall the 3CPC-Mt-p catalysts had a strong anti-interference ability, showing good application prospects. The quenching experiments and EPR tests showed that O2-- and 1O2 in the 3CPC-Mt-p/PMS system were the main reactive oxygen species for the degradation of OFL, and •OH was also involved in the reaction. This study provides ideas for the construction and modulation of active sites in mineral materials such as montmorillonite and broadens the application of montmorillonite composite catalysts in advanced oxidation processes for the treatment of antibiotic wastewater.

Printable High-Efficiency and Stable FAPbBr3 Perovskite Solar Cells for Multifunctional Building-Integrated Photovoltaics.

Perovskite solar cells (PSCs) show great promise for next-generation building-integrated photovoltaic (BIPV) applications because of their abundance of raw materials, adjustable transparency, and cost-effective printable processing. Owing to the complex perovskite nucleation and growth control, the fabrication of large-area perovskite films for high-performance printed PSCs is still under active investigation. Herein, the study proposes an intermediate-phase-transition-assisted one-step blade coating for an intrinsic transparent formamidinium lead bromide (FAPbBr3 ) perovskite film. The intermediate complex optimizes the crystal growth path of FAPbBr3 , resulting in a large-area, homogeneous, and dense absorber film. A champion efficiency of 10.86% with high open-circuit voltage up to 1.57 V is obtained with a simplified device architecture of glass/FTO/SnO2 /FAPbBr3 /carbon. Moreover, the unencapsulated devices maintain 90% of their initial power conversion efficiency after aging at 75 °C for 1000 h in ambient air, and 96% after maximum power point tracking for 500 h. The printed semitransparent PSCs, with average visible light transmittance over 45%, demonstrate high efficiencies for both small devices (8.6%) and 10 × 10 cm2 modules (5.55%). Finally, the ability to customize the color, transparency, and thermal insulation properties of FAPbBr3 PSCs makes them high prospects as multifunctional BIPVs.

Low-Cost Fabrication of Efficient Perovskite Photovoltaics Using Low-Purity Lead Iodide via Powder Engineering.

Low cost is the eternal theme for any commercial production. Numerous efforts have been explored to realize low-cost, high-efficiency perovskite solar cells (PSCs), such as replacing the traditional spin-coating method with an economical printing strategy, simplifying the device structure, reducing the number of functional layers, etc. However, there are few reports on the use of low-cost precursors. Herein, we enable the low-cost fabrication of efficient PSCs based on a very cheaper low-purity PbI2 via powder engineering. The low-purity PbI2 is blended with formamidinium iodide followed by dissolving in a 2-methoxyethanol solvent, and then, the high-quality FAPbI3 powders are formed via an inverse temperature crystallization process and solvent washing after several simple processes to reduce the impurities. As a result, the devices fabricated using the as-synthesized black powders based on the low-purity PbI2 exhibit a champion power conversion efficiency (PCE) of 23.9% and retained ∼95% of the initial PCE after ∼400 h of storage in the conditions of 25 ± 5 °C and 25 ± 5 RH% without encapsulation. In addition, the upscaling fabrication of a 5 cm × 5 cm solar minimodule also demonstrates an impressive efficiency of 19.5%. Our findings demonstrate an economic strategy for the commercialization of PSCs from the perspective of low-cost production.

Spiky mesoporous anatase titania beads: a metastable ammonium titanate-mediated synthesis.

A complex titania nanostructure of monodisperse spiky mesoporous anatase beads composed of anatase nanocrystals with diameters of less than 15 nm in the core and much larger hollow-cone shaped spikes on the surface was fabricated using a facile solvothermal process in the presence of ammonia. This proceeded through a controllable phase transformation from an amorphous titania to a metastable amorphous titania/ammonium titanate core-shell structure then finally to anatase titania. The size of the spiky anatase nanostructures can be increased from approximately 55 × 100 nm to 160 × 410 nm (square edge × length) by increasing the ammonia concentration used in the solvothermal treatment step from 2.2 to 17.4 wt. %. Such hollow-cone shaped nanostructures, as revealed by HRTEM characterization, are single crystals elongated along the c axis of the tetragonal anatase titania. The resultant spiky titania beads have high surface areas of up to 112 m(2) g(-1) and pore diameters and pore volumes that vary depending on the ammonia concentration and solvothermal treatment time. The morphological evolution and crystallization process of the spiky titania beads was investigated using SEM and XRD techniques. A metastable amorphous titania/ammonium titanate core-shell structure evolved from the smooth amorphous precursor beads producing a "fluffy" titanate intermediate, on further heating the final spiky mesoporous titania beads were clearly observed. This titanate-phase-mediated approach allows control over the size of the nanocrystals in the core of the bead, as well as the anatase spikes on the surface, and thereby, tuning of the surface area and porosity of the resultant products. The spiky mesoporous titania beads have been used to prepare working electrodes for dye-sensitized solar cells achieving a solar to electric power conversion efficiency of 10.30 %, indicating their potential for application in the photovoltaic field. Such complex titania nanostructures would have a number of other possible applications, such as photocatalysis, lithium ion batteries, and catalysis.

Spontaneous redox synthesis of the charge transfer material TTF4[SVMo11O40].

The charge-transfer material TTF-SV(IV)Mo(11)O(40) (TTF = tetrathiafulvalene) was prepared by a spontaneous redox reaction between TTF and the vanadium-substituted polyoxometalate (n-Bu(4)N)(3)[SV(V)Mo(11)O(40)] in both solution and solid state phases. Single crystal X-ray diffraction gave the stoichiometry TTF(4)[SVMo(11)O(40)]·2H(2)O·2CH(2)Cl(2), with the single V atom positionally disordered with eight Mo atoms over the whole α-Keggin polyanion [SVMo(11)O(40)](4-). Raman spectra support the 1+ charge assigned to the oxidized TTF deduced from bond lengths, and elemental and voltammetric analysis also are consistent with this formulation. Scanning electron microscopy images showed a rod-type morphology for the new charge-transfer material. The conductivity of the solid at room temperature is in the semiconducting range. The TTF and (n-Bu(4)N)(3)[SV(V)Mo(11)O(40)] solids also undergo a rapid interfacial reaction, as is the case with TTF and TCNQ (TCNQ = tetracyanoquinodimethane) solids. EPR spectra at temperatures down to 2.6 K confirm the presence of two paramagnetic species, V(IV) and the oxidized TTF radical. Spectral evidence shows that the TTF-SV(IV)Mo(11)O(40) materials prepared from either solution or solid state reactions are equivalent. The newly isolated TTF-SV(IV)Mo(11)O(40) material represents a new class of TTF-polyoxometalate compound having dual electrical and magnetic functionality derived from both the cationic and anionic components.

Mitigating the Internal Ion Migration of Organic-Inorganic Hybrid Perovskite by a Graphene Oxide Interlayer.

Organic-inorganic hybrid perovskite solar cells (PSCs) have attracted great research attention due to their outstanding optoelectronic properties. The low-temperature synthesizing process of organic-inorganic hybrid perovskites can provide a significant advantage of reducing the manufacturing cost of solar cells. However, at the same time, this also brings challenges to PSCs in the form of long-term stability. Because of the low vacancy formation energy, organic-inorganic hybrid perovskites suffer from serious ion migration issue. Also, this ion migration will lead to a series of stability problems, which can hardly be addressed by encapsulation. Currently, modifying the surface of perovskite by an ion-blocking layer is a common strategy for achieving highly stable PSCs. These strategies could effectively address the stability issues caused by the interfacial ion diffusion between perovskite and the charge transport layer. However, the ion migration inside the perovskite layer could be still a knotty problem, which is difficult to be solved through surface modification. Herein, we propose a novel strategy to mitigate the internal ion migration by inserting two-dimensional graphene oxide (GO) into a perovskite layer. Close-space sublimation and ultrasonic spray coating were employed to prepare perovskite and GO layers, respectively. We found that the ion migration in the as-prepared perovskite/GO/perovskite can be successfully mitigated by the GO interlayer. As a result, the champion PSC with a GO interlayer maintained 85% of its initial power conversion efficiency (PCE) after 96 h of continuous illumination. By contrast, the efficiency of the PSC without a GO interlayer declined rapidly and maintained only 50% of the initial value. We believe that this novel interlayer strategy could provide a new idea and approach to preparing highly stable PSCs.

Highly Crystalline Graphene as the Atomic 2D Blanket of a Perovskite Absorber for Enhanced Photovoltaic Performance.

Perovskite solar cells (PSCs) have demonstrated enormous potential for next-generation low-cost photovoltaics. However, due to the intrinsically low bond energy of the perovskite lattice, the long-term stability is normally undermined by ion migration initiated by the electric field and atmospheric conditions. Therefore, ideal ion migration inhibition is important to achieve an enhanced stability of PSCs. Herein, we first introduce a chemical vapor deposition (CVD) fabricated highly crystalline graphene as an atomic 2D blanket directly for the perovskite absorber of PSCs. Iodine and lithium ion migration is effectively inhibited for perovskite solar cells under a continuous static electric field. The water and oxygen corrosion of the unencapsulated device has been dramatically mitigated with atomic graphene blanketing on the perovskite film. With triphenylamine (TPA) molecule modification, the photoconversion efficiencies (PCEs) of the blanketed devices reach 21.54%. The sample with blanket graphene maintains 85% of the initial efficiency, in comparison to 52% of the control sample under voltage bias. After 600 h of aging at 25 °C and 55 RH%, 86% in comparison to <30% of the PCE for the control device is obtained for the sample with a graphene blanket. Thus, we propose that crystalline graphene has an excellent and effective ion-blocking blanket potential for highly stable perovskite devices.

All-vacuum deposited perovskite solar cells with glycine modified NiO x hole-transport layers.

Organic-inorganic hybrid perovskite solar cells (PSCs) have attracted enormous research attention due to their high efficiency and low cost. However, most of the PSCs with high efficiencies still need expensive organic materials as their hole-transport layer (HTL). Obviously, the highly expensive materials go against the low-cost concept of advanced PSCs. In this regard, inorganic NiO x was considered as an idea HTL due to its good transmittance in the visible region and outstanding chemical stability. But for most of the PSCs with a NiO x HTL, the hole-extraction efficiency was limited by the unmatched valence band and too many surface defects of the NiO x layer, especially for the vacuum-deposited NiO x and perovskite. Herein, we developed a facile strategy to overcome this issue by using self-assembled glycine molecules to treat the NiO x surface. With glycine on the surface, the NiO x exhibited a deeper valence band maximum and a faster charge-extraction at the NiO x /perovskite interface. What's more, the vacuum-deposited perovskite showed a better crystallinity on the NiO x + glycine substrate. As a result, the PSCs with a glycine interfacial layer achieved a champion PCE of 17.96% with negligible hysteresis. This facile approach is expected to be further developed for fabricating high-efficiency PSCs on textured silicon solar cells.