Perovskite solar cells increasingly feature mixed‐halide mixed‐cation compounds (FA1−x−yMAxCsyPbI3−zBrz) as photovoltaic absorbers, as they enable easier processing and improved stability. Here, the ...underlying reasons for ease of processing are revealed. It is found that halide and cation engineering leads to a systematic widening of the anti‐solvent processing window for the fabrication of high‐quality films and efficient solar cells. This window widens from seconds, in the case of single cation/halide systems (e.g., MAPbI3, FAPbI3, and FAPbBr3), to several minutes for mixed systems. In situ X‐ray diffraction studies reveal that the processing window is closely related to the crystallization of the disordered sol–gel and to the number of crystalline byproducts; the processing window therefore depends directly on the precise cation/halide composition. Moreover, anti‐solvent dripping is shown to promote the desired perovskite phase with careful formulation. The processing window of perovskite solar cells, as defined by the latest time the anti‐solvent drip yields efficient solar cells, broadened with the increasing complexity of cation/halide content. This behavior is ascribed to kinetic stabilization of sol–gel state through cation/halide engineering. This provides guidelines for designing new formulations, aimed at formation of the perovskite phase, ultimately resulting in high‐efficiency perovskite solar cells produced with ease and with high reproducibility.
The role of cation and halide mixing is revealed using in situ X‐ray scattering measurements during spin‐coating. Modulating the cation/halide composition directly impacts the lifetime of the sol–gel precursor film and its easy and reproducible conversion to the perovskite phase to yield solar cells with 20% power conversion efficiency.
To investigate the effectiveness of nutritional supplement Bao Khi Khang as an adjuvant therapy in acute exacerbations of chronic obstructive pulmonary disease (COPD) compared to conventional therapy ...alone. This was a prospective, randomized, open-label controlled trial in 60 patients presenting with acute exacerbation of COPD. Patients were randomized into two groups, the control and the experimental groups. The control group was treated with the standard therapeutic protocol (Antimicrobial+Corticosteroids+Bronchodilator+Mucolytic drugs). The experimental group was treated with Bao Khi Khang tablets combined with the standard therapeutic protocol. The treatment outcomes, including clinical and paraclinical parameters of exacerbation of COPD, were compared between the experimental group and the control group at day 15 and 30. This study was conducted according to protocol: 01.2014-HTNCKH. The results showed a significant reduction of major COPD exacerbation symptoms in experimental group. The favorable progresses in mMRC scale and COPD Assessment Test score before and after treatment, between experimental group and control group, were statistically different. Symptom control such as cough, copious sputum secretion, and bacterial infection was 90% effective (very good 50.0%, good 40.0%) in experimental group compared to 50% (very good 20%, good 30.0%) in control group. No adverse side effects were observed in experimental group. Bao Khi Khang nutritional supplement could be an effective and safe adjuvant therapy in acute exacerbations of COPD. Further interventional studies are required to confirm these findings.
Metal-halide perovskites feature very low deep-defect densities, thereby enabling high operating voltages at the solar cell level. Here, by precise extraction of their absorption spectra, we find ...that the low deep-defect density is unaffected when cations such as Cs+ and Rb+ are added during the perovskite synthesis. By comparing single crystals and polycrystalline thin films of methylammonium lead iodide/bromide, we find these defects to be predominantly localized at surfaces and grain boundaries. Furthermore, generally, for the most important photovoltaic materials, we demonstrate a strong correlation between their Urbach energy and open-circuit voltage deficiency at the solar cell level. Through external quantum yield photoluminescence efficiency measurements, we explain these results as a consequence of nonradiative open-circuit voltage losses in the solar cell. Finally, we define practical power conversion efficiency limits of solar cells by taking into account the Urbach energy.
Perovskite photovoltaics have made extraordinary strides in efficiency and stability thanks to process and formulation developments like anti-solvent dripping and mixed-cation mixed-halide ...compositions. Solar cell fabrication through low-cost scalable methods, such as blade coating, cannot accommodate anti-solvent dripping and needs to be performed in an ambient atmosphere. Consequently, their efficiency has lagged behind that of spin-cast devices, fabricated in an inert atmosphere and with carefully timed anti-solvent dripping to control nucleation and growth. In this study, we demonstrate formamidinium (FA)-dominated mixed-halide mixed-cation perovskite solar cells fabricated by blade coating in ambient air ( T = 23 °C and RH ≈ 50%) without the benefits of anti-solvent dripping or a moisture-free environment. We investigated the solidification process during blade coating of single-cation (FAPbI 3 ) and increasingly complex mixed-cation mixed-halide (FA 0.8 MA 0.15 Cs 0.05 PbI 2.55 Br 0.45 , MA is methylammonium) perovskites in situ using time-resolved grazing incidence wide-angle X-ray scattering (GIWAXS). We found that the perovskite precursor composition and the blade coating temperature profoundly influence the crystallization mechanism and whether halide segregation occurs or not. The inclusion of Br − suppresses the non-perovskite 2H phase, promoting instead PbI 2 together with the intermediate 6H phase and 3C phase of FAPbI 2.55 Br 0.45 . Addition of Cs + suppresses these intermediates and promotes the direct crystallization of the perovskite 3C phase FA 0.8 MA 0.15 Cs 0.05 PbI 2.55 Br 0.45 when coating at elevated temperature, unlike when anti-solvent dripping is used at room temperature. Through control of ink formulation and coating conditions, we demonstrate blade coated perovskite solar cells with a champion power conversion efficiency (PCE) of 18.20% as compared with FAPbI 3 perovskites, which yield a PCE of 12.35% under similar conditions without the benefit of anti-solvent dripping. This study provides valuable insight into the crystallization pathway of mixed-cation mixed-halide formulations without anti-solvent dripping under high-temperature processing conditions that enable the translation of perovskites toward upscalable ambient manufacturing under high throughput conditions.
Nanostructured Ta3N5 photoanodes (band gap of ∼2.0 eV) were synthesized via a two-step process: first, nanocolumnar Ta2O5 films were deposited by evaporation of tantalum metal in a vacuum chamber in ...a low pressure oxygen ambient followed by heating in an ammonia gas flow to convert Ta2O5 into orthorhombic Ta3N5. Under Xe lamp irradiation (∼73 mW/cm2), a 100 nm nanoporous Ta3N5 electrode achieved an anodic photocurrent of ∼1.4 mA/cm2 at +0.5 V versus Ag/AgCl in 1 M KOH solution. By comparison, a dense film achieved ∼0.4 mA/cm2 clearly illustrating the importance of nanostructuring for improving the performance of Ta3N5 photoanodes. However, Ta3N5 films suffered from inherent self-oxidation under light illumination, and application of a cobalt cocatalyst layer was found to improve the stability as well as photocatalytic activity of the Ta3N5 films.
Tantalum cobalt nitride photocatalysts were prepared using a simple drop coating method on a Ta foil substrate followed by thermal ammonia treatment, and their photoelectrochemical (PEC) properties ...for water oxidation under visible light were studied. The resulting Ta0.9Co0.1N x films showed a photocurrent of ca. 1.5 mA/cm2 (12 times higher than that of Ta3N5) under 100 mW/cm2 visible light irradiation at 0.7 V vs Ag/AgCl in a 0.1 M Na2SO4 aqueous solution (pH 11). The good PEC performance was attributed to the introduction of cobalt and the formation of cobalt nitride, which efficiently facilitates electron transfer and suppresses the recombination of photogenerated electron–hole pairs. Some cobalt nitride could further be oxidized to generate cobalt oxide, which serves as an efficient electrocatalyst for water oxidation. The enhanced visible light activity and film stability under light irradiation make tantalum cobalt nitride a promising semiconductor for PEC water oxidation.
Tantalum nitride (Ta3N5) is a promising material for photoelectrochemical (PEC) water oxidation with a narrow band gap (2.1 eV) that can effectively utilize visible light in the solar spectrum. Ta3N5 ...nanotube (NT) arrays were synthesized on a Ta foil by electrochemical anodization followed by an ammonia treatment at 800 °C. The photocurrent of nanostructured Ta3N5 was over 3 times higher than that of a dense regular Ta3N5 film in 0.1 M Na2SO4 aqueous solution at pH 11. Several electrocatalysts (IrO2 nanoparticles (NPs), Co3O4 NPs, cobalt phosphate, and Pt NPs) were used to modify Ta3N5 NTs for PEC water oxidation. The photocurrent of Ta3N5 NTs modified with IrO2 and Co3O4 was ca. four times higher than that of unmodified NTs. Cobalt phosphate also showed a positive improvement for PEC water oxidation on Ta3N5 NTs, whereas Pt was ineffective. Scanning electrochemical microscopy was used to measure the faradaic efficiency of the Ta3N5 photoanodes for water oxidation, which can reach as high as 88% for a Co3O4–Ta3N5 NTs photoanode, but is less than 15% at best, for Ta3N5 without the electrocatalyst. The results indicate that cobalt oxide and cobalt phosphate are promising candidates as electrocatalysts on Ta3N5 for water oxidation because Co is an earth-abundant material.
In a 100 cycle test at 0.5 C-rate a negative electrode formed of micro-sized Sn 0.9 Se 0.1 particles retains a specific capacity of 500 mA h g −1 with a coulombic efficiency of 99.6%. In contrast, a ...control electrode made with pure Sn retains only a 200 mA h g −1 capacity with a 98.7% efficiency. The improvement in electrochemical performance of the Sn/Se alloy is attributed to the reduced inactive Se-phase preventing agglomeration of Sn to a size susceptible to particle fracture. The Sn/Se alloy particles are manufacturable, being made by melting the 9 : 1 atomic ratio mixture of Sn and Se, quenching and jet-milling.
NiV2O6 films were successfully fabricated and characterized as photoanodes for photoelectrochemical (PEC) water oxidation. The films were synthesized by vacuum codeposition of Ni and V followed by ...annealing in air. The resulting triclinic NiV2O6 films were n-type semiconductors with optical transitions at ∼2.1 eV (indirect) and 2.4 eV (direct). Photoelectrochemical testing in 1 M KOH showed a photoelectrochemical band gap of ∼2.4 eV and that ∼45% of the photocurrent came from light with λ > 420 nm. NiV2O6 electrodes showed quite stable photocurrent under bias in basic electrolyte, indicative of chemical stability against photocorrosion despite its relatively small band gap. The flat band potential of NiV2O6 was ∼0.6 V vs RHE, thus allowing photogenerated holes to oxidize water thermodynamically, and confirmed by oxygen evolution measurements (Faradaic efficiency ∼80%). Suitable oxygen evolution catalysts and n-type doping are suggested to improve the PEC performance of this material further. Regarding the search for inexpensive photoanodes capable of harvesting photons in the visible region of the solar spectrum, the availability of Ni and V makes NiV2O6 a promising anode material for photoelectrochemical use.
Tin forms a series of sodium alloys, some with a large change in volume, sufficient to fracture the sodiated/de-sodiated tin electrodes. In a series of Sn/C and Sn/Se/C electrodes, made similarly by ...ball milling the elements, the sodiation/de-sodiation cycling stability in the 0.01-1.00 V vs. Na+/Na voltage window, in which the initially formed Na2Se is electrochemically inactive, is best at an Sn : Se atomic ratio of 9 : 2. At this ratio the retained capacity is similar to 300 mA h g-1 after 150 cycles at 0.17 A g-1 rate versus only 70 mA h g-1 in the absence of Na2Se. The improvement is attributed to prevention of crystallization of the Na-Sn alloys by the Na2Se.
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