Eliminating Halogen Vacancies Enables Efficient MACL-Assisted Formamidine Perovskite Solar Cells.

Methylammonium chloride (MACl) additive is almost irreplaceable in high-performance formamidine perovskite photovoltaics. Nevertheless, Some of the problems that can arise from adding MACl are rarely mentioned. Herein, it is proposed for the first time that the addition of MACl would cause the non-stoichiometric ratio in the perovskite film, resulting in the halogen vacancy. It is demonstrated that the non-synchronous volatilization of methylamine cations and chloride ions leads to the formation of halogen vacancy defects. To solve this problem, the NH4 HCOO is introduced into the perovskite precursor solution to passivate the halogen vacancy. The HCOO- ions have a strong force with lead ions and can fill the halogen vacancy defects. Consequently, the champion devices' power conversion efficiency (PCE) can be improved from 21.23% to 23.72% with negligible hysteresis. And the unencapsulated device can still retain >90% of the initial PCE even operating in N2 atmosphere for over 1200 h. This work illustrates another halogen defect source in the MACl-assisted formamidine perovskite photovoltaics and provides a new route to obtain high-performance perovskite solar cells.

Lattice Strain Regulation Enables High-Performance Formamidinium Perovskite Photovoltaics.

Formamidinium lead iodide (FAPbI3 ) perovskite possesses an ideal optical bandgap and is a potential material for fabricating the most efficient single-junction perovskite solar cells (PSCs). Nevertheless, large formamidinium (FA) cations result in residual lattice strain, which reduces the power conversion efficiency (PCE) and operational stability of PSCs. Herein, the modulation of lattice strain in FAPbI3 crystals via a π-conjugated organic amine, i.e., 4-pyrene oxy butylamine (PYBA), is proposed. PYBA pairs at the grain boundary serve as a template for the crystallization of FAPbI3 perovskite, thereby inducing a highly oriented crystal and a pure α-phase film. The PYBA pairs with strong π-π interactions provide a solid fulcrum for external compression strain, thus compensating for the inherent tension strain of FAPbI3 crystals. The strain release elevates the valence band of the perovskite crystals, thereby decreasing the bandgap and trap density. Consequently, the PYBA-regulated FAPbI3 PSC achieves an excellent PCE of 24.76%. Moreover, the resulting device exhibits improves operational stability and maintains over 80% of its initial PCE after 1500 h under maximum power point tracking conditions.

Enhanced Performance of CsPbIBr2 Perovskite Solar Cell by Modified Zinc Oxide Nanorods Array with [6,6]-Phenyl C61 Butyric Acid.

Although Metal oxide ZnO is widely used as electron transport layers in all-inorganic PSCs due to high electron mobility, high transmittance, and simple preparation processing, the surface defects of ZnO suppress the quality of perovskite film and inhibit the solar cells' performance. In this work, [6,6]-Phenyl C61 butyric acid (PCBA) modified zinc oxide nanorods (ZnO NRs) is employed as electron transport layer in perovskite solar cells. The resulting perovskite film coated on the zinc oxide nanorods has better crystallinity and uniformity, facilitating charge carrier transportation, reducing recombination losses, and ultimately improving the cells' performance. The perovskite solar cell with the device configuration of ITO/ZnO nanorods/PCBA/CsPbIBr2 /Spiro-OMeTAD/Au delivers a high short circuit current density of 11.83 mA cm-2 and power conversion efficiency of 12.05 %.

Perylene Monoimide Phosphorus Salt Interfacial Modified Crystallization for Highly Efficient and Stable Perovskite Solar Cells.

Reducing the interfacial defects of perovskite films is key to improving the performance of perovskite solar cells (PSCs). In this study, two kinds of perylene monoimide (PMI) derivative phosphonium bromide salts were designed and used as a multifunctional interface-modified layer in PSCs. These two molecules are inserted between SnO2 and perovskite to produce a bidirectional passivation effect. The interaction with SnO2 reduces the oxygen vacancy on the surface of SnO2 and tunes the energy level of the electron transport layer, making more matches with the perovskite layer. The modified layer can promote the growth of perovskite crystals and reduce the interfacial defects of the perovskite film. Furthermore, the power conversion efficiency (PCE) of PSCs increased from 19.49 to 22.85%, and the open-circuit voltage (VOC) increased from 1.06 to 1.14 V. At the same time, the PCE of the SnO2/PMI-TPP-based device remained 88% of the initial PCE after 240 h of continuous illumination. In addition, these two PMI derivatives with a quasi-planar structure can improve the flexibility of flexible PSCs. This study provided a new strategy for the interfacial modification of PSCs and a new insight into the application of flexible PSCs.

Synthesis-on-substrate of quantum dot solids.

Perovskite light-emitting diodes (PeLEDs) with an external quantum efficiency exceeding 20% have been achieved in both green and red wavelengths1-5; however, the performance of blue-emitting PeLEDs lags behind6,7. Ultrasmall CsPbBr3 quantum dots are promising candidates with which to realize efficient and stable blue PeLEDs, although it has proven challenging to synthesize a monodispersed population of ultrasmall CsPbBr3 quantum dots, and difficult to retain their solution-phase properties when casting into solid films8. Here we report the direct synthesis-on-substrate of films of suitably coupled, monodispersed, ultrasmall perovskite QDs. We develop ligand structures that enable control over the quantum dots' size, monodispersity and coupling during film-based synthesis. A head group (the side with higher electrostatic potential) on the ligand provides steric hindrance that suppresses the formation of layered perovskites. The tail (the side with lower electrostatic potential) is modified using halide substitution to increase the surface binding affinity, constraining resulting grains to sizes within the quantum confinement regime. The approach achieves high monodispersity (full-width at half-maximum = 23 nm with emission centred at 478 nm) united with strong coupling. We report as a result blue PeLEDs with an external quantum efficiency of 18% at 480 nm and 10% at 465 nm, to our knowledge the highest reported among perovskite blue LEDs by a factor of 1.5 and 2, respectively6,7.

Semi-Planar Non-Fullerene Molecules Enhance the Durability of Flexible Perovskite Solar Cells.

Flexible perovskite solar cells (FPSCs) represent a promising technology in the development of next-generation photovoltaic and optoelectronic devices. SnO2 electron transport layers (ETL) typically undergo significant cracking during the bending process of FPSCs, which can significantly compromise their charge transport properties. Herein, the semi-planar non-fullerene acceptor molecule Y6 (BT-core-based fused-unit dithienothiophen [3,2-b]-pyrrolobenzothiadiazole derivative) is introduced as the buffer layer for SnO2 -based FPSCs. It is found that the Y6 buffer layer can enhance the ability of charge extraction and bending stability for SnO2 ETL. Moreover, the internal stress of perovskite films is also reduced. As a result, SnO2 /Y6-based FPSCs achieved a power conversion efficiency (PCE) of 20.09% and retained over 80% of their initial efficiency after 1000 bending cycles at a curvature radius of 8 mm, while SnO2 -based devices only retain 60% of their initial PCE (18.60%) upon the same bending cycles. In addition, the interfacial charge extraction is also effectively improved in conjunction with reduced defect density upon incorporation of Y6 on the SnO2 ETL, as revealed by femtosecond transient absorption (Fs-TA) measurements.

Tuning Surface Wettability of Buffer Layers by Incorporating Polyethylene Glycols for Enhanced Performance of Perovskite Solar Cells.

Phenyl-C61-butyric acid methyl ester (PCBM) has been widely researched as a passivate electron transport layer in planar n-i-p-type perovskite solar cells (PSCs). However, due to the terrible wettability of PCBM, the growth of perfect large-area perovskite films on the electron transport layer treated by PCBM is a huge challenge, which limits the commercial application of PSCs. Herein, we incorporate a hydrophilic polymer polyethylene glycol (PEG) into PCBM to ameliorate its wettability. A high-quality perovskite film can be prepared on a 2 × 2 cm substrate. Hydrogen-bonding effects between the PEG-PCBM buffer layer and the perovskite layer can further stabilize the electron transport layer/perovskite interface. Based on the improved electron transport and suppressed carrier recombination, a device with an active area of 1.03 cm2 achieves an efficiency of 18.25%. In addition, the first-principles calculations indicate that PEG has stronger adsorption (Eads = -0.37) toward H2O than the MAPbI3 perovskite (Eads = -0.25), which can prevent water molecules from infiltrating the perovskite. The unsealed device still maintains 90% of the initial efficiency under ambient conditions, with 30-40% relative humidity for 22 days. These outstanding properties are attributed to the unique molecular structure and prominent wettability of PEG.

Reduced-dimensional perovskite photovoltaics with homogeneous energy landscape.

Reduced-dimensional (quasi-2D) perovskite materials are widely applied for perovskite photovoltaics due to their remarkable environmental stability. However, their device performance still lags far behind traditional three dimensional perovskites, particularly high open circuit voltage (Voc) loss. Here, inhomogeneous energy landscape is pointed out to be the sole reason, which introduces extra energy loss, creates band tail states and inhibits minority carrier transport. We thus propose to form homogeneous energy landscape to overcome the problem. A synergistic approach is conceived, by taking advantage of material structure and crystallization kinetic engineering. Accordingly, with the help of density functional theory guided material design, (aminomethyl) piperidinium quasi-2D perovskites are selected. The lowest energy distribution and homogeneous energy landscape are achieved through carefully regulating their crystallization kinetics. We conclude that homogeneous energy landscape significantly reduces the Shockley-Read-Hall recombination and suppresses the quasi-Fermi level splitting, which is crucial to achieve high Voc.

A Chiral Reduced-Dimension Perovskite for an Efficient Flexible Circularly Polarized Light Photodetector.

Chiral quasi-2D perovskite single crystals (SCs) were investigated for their circular polarized light (CPL) detecting capability. Quasi-2D chiral perovskites, [(R)-ß-MPA]2 MAPb2 I7 ((R)-ß-MPA=(R)-(+)-ß-methylphenethylamine, MA=methylammonium), have intrinsic chirality and the capability to distinguish different polarization states of CPL photons. Corresponding quasi-2D SCs CPL photodetector exhibit excellent detection performance. In particular, our device responsivity is almost one order of magnitude higher than the reported 2D perovskite CPL detectors to date. The crystallization dynamics of the film were modulated to facilitate its carrier transport. Parallel oriented perovskite films with a homogeneous energy landscape is crucial to maximize the carrier collection efficiency. The photodetector also exhibits superior mechanical flexibility and durability, representing a promising candidate for sensitive and robust CPL photodetectors.

An efficient and stable inverted perovskite solar cell involving inorganic charge transport layers without a high temperature procedure.

Despite the successful enhancement in the high-power conversion efficiency (PCE) of perovskite solar cells (PSCs), the poor stability of PSCs is one of the major issues preventing their commercialization. The attenuation of PSCs may be due to the lower heat resistance of the organic charge transport layer and the tendency to aggregate at high temperatures. Here we report cerium oxide (CeO x ) as an electron transport layer (ETL) prepared through a simple solution processed at a low temperature (∼100 °C) to replace the organic charge transport layer on top of the inverted planar PSCs. The CeO x layer has excellent charge selectivity and can provide the perovskite film with protection against moisture and metal reactions with the electrode. The solar cell with CeO x as the electron transport layer has a power conversion efficiency of 17.47%. These results may prove a prospect for practical applications.

Effect of Molecular Structures of Donor Monomers of Polymers on Photovoltaic Properties.

This work investigates the photovoltaic properties of polymers that include different carbazole blocks as electron donors (D) but the same benzothiadiazole derivative as the electron acceptor (A). Five D-A copolymers are studied with ultrafast intramolecular exciton splitting and recombination dynamics to acquire the single-molecule structure and their photovoltaic performance relationship. The photovoltaic parameters such as energy level, optical band gap, and light-harvesting ability are highly dependent on the molecular structure of the donor monomer (including their appended flexible alkyl chain). Branched or linear alkyl groups on the same D block obviously vary the polymer steady-state absorption spectra and film morphology. For organic solar cells, this work allows tuning and control of the ultrafast dynamics, implying photovoltaic material design in the future.

All-Inorganic Perovskite Solar Cells Based on CsPbIBr2 and Metal Oxide Transport Layers with Improved Stability.

Despite the successful improvement in the power conversion efficiency (PCE) of perovskite solar cells (PSCs), the issue of instability is still a serious challenge for their commercial application. The issue of the PSCs mainly originates from the decomposition of the organic-inorganic hybrid perovskite materials, which will degrade upon humidity and suffer from the thermal environment. In addition, the charge transport layers also influence the stability of the whole devices. In this study, inorganic transport layers are utilized in an inverted structure of PSCs employing CsPbIBr2 as light absorbent layer, in which nickel oxide (NiOx) and cerium oxide (CeOx) films are applied as the hole transport layer (HTL) and the electron transport layer (ETL), respectively. The inorganic transport layers are expected to protect the CsPbIBr2 film from the contact of moisture and react with the metal electrode, thus preventing degradation. The PSC with all inorganic components, inorganic perovskite and inorganic transport layers demonstrates an initial PCE of 5.60% and retains 5.56% after 600 s in ambient air at maximum power point tracking.

Stable isotope dilution assay for the accurate determination of tricaine in fish samples by HPLC-MS-MS.

Tricaine methanesulfonate is one of most commonly used anesthetics in fish during blood sampling, artificial propagation and long-distance transportation. In this study, an accurate method for the quantitative determination of tricaine in fish samples by a stable isotope dilution assay coupled with high-performance liquid chromatography-triple quadrupole mass spectrometry was developed. Tricaine-D5 was synthesized and used as an isotopically labeled internal standard for the determination of tricaine. The analytical performance of the method was validated for tricaine determination in marine fish and freshwater fish. The determination of tricaine was linear in the range of 2.0-200.0 µg L-1 . The limit of detection and limit of quantitation for fish muscle tissues were 1.0 and 4.0 µg kg-1 , respectively. Good recoveries were obtained in the range of 92.08-97.50%. The inter- and intra-assay relative standard deviations (RSD values) were investigated, and the values were 0.39-3.01 and 0.85-2.77%, respectively. The values of CCα and CCß were 10.21-10.43 and 10.42-10.87 µg kg-1 , respectively. The clearance of MS-222 from grass carp was further studied using our method. The results demonstrate that MS-222 could be well absorbed and rapidly eliminated after bath administration.

Stable isotope labeling-assisted GC/MS/MS method for determination of methyleugenol in food samples.

BACKGROUND: Methyleugenol is a common phenylpropanoid compound found in many plants and has been widely used as a flavoring agent in people's daily life. In this study, a stable isotope dilution assay-coupled gas chromatography/triple quadrupole mass spectrometry (SIDA-GC/MS/MS) method was developed for the quantitative determination of methyleugenol in food samples. Methyleugenol-D3 was synthesized and used as an isotope internal standard for the determination of methyleugenol. The QuEChERS (quick, easy, cheap, effective, rugged and safe) method was applied to the clean-up of food sample extracts. Confirmation and quantification were carried out by GC/MS/MS. RESULTS: The analytical performance of the method was validated. The determination range of methyleugenol was linear from 4 to 500 µg L-1 . Method detection limits for solid food samples, semi-solid food samples and liquid beverages were 50, 50 and 1 µg kg-1 respectively. Satisfactory recoveries in the range 94.29-100.27% were obtained. Intra- and inter-day precision was also validated and the values were all lower than 9%. The method was successfully applied to quantify methyleugenol in different kinds of food samples. CONCLUSION: This article describes a new method for the accurate quantification of methyleugenol in food samples based on a stable isotope labeling-assisted GC/MS/MS method. Methyleugenol-D3 was synthesized and used as an isotope internal standard for the determination of methyleugenol. Excellent results were generated with the method, and the detection sensitivity and accuracy of the method were good. © 2018 Society of Chemical Industry.

Preparation and Photocatalytic Performance of Hollow Structure LiNb3O8 Photocatalysts.

Hollow structure LiNb3O8 photocatalysts were prepared by a hydrothermal method assisting sintering process. The particles' aggregation to form hollow structures with obvious cavities can be attributed to the Li element volatilization during calcination process. All the LiNb3O8 powders show high photocatalytic efficiency of degradation of methylene blue (MB), especially for the sample calcined at 700 °C (LNO700), with only 3 h to completely decompose MB. The photo-degradation of MB follows the pseudo-first-order kinetics, and the obtained first-order rate is 0.97/h. The larger degradation rate of LNO700 can be attributed to its hollow structure which provides a larger specific surface area and more active sites to degrade the MB molecules. The cycling test of photo-degradation and adsorption of MB over LNO700 powder indicates that the hollow structure of the LiNb3O8 photocatalyst is stable and the LiNb3O8 photocatalyst is an efficient photocatalyst with good reusability, confirmed by the XRD and X-ray photoelectron spectroscopy tests before and after photo-degradation of MB.

The Effects of Li/Nb Ratio on the Preparation and Photocatalytic Performance of Li-Nb-O Compounds.

The effects of Li/Nb ratio on the preparation of Li-Nb-O compounds by a hydrothermal method were studied deeply. Li/Nb ratio has a great impact on the formation of LiNbO3; the ratio smaller than 3:1 is beneficial to the formation of LiNbO3, while larger than 3:1, forms no LiNbO3 at all and the morphology and chemical bond of Nb2O5 raw material are totally modified by Li ions. The reason can be attributed to the large content of LiOH, which is beneficial to form Li3NbO4 not LiNbO3, and also, even if LiNbO3 particle locally forms, it is easily dissolved in LiOH solution with strong alkalinity. Pure LiNb3O8 powders are obtained with two absolutely opposite Li/Nb ratios: 8:1 and 1:3; the former shows a unique porous and hollow structure, quite different from the particle aggregation (the latter shows). Compared with Li/Nb = 1:3, the 4.2 times higher photocatalytic performance of LiNb3O8 (Li/Nb = 8:1) are observed and it can be attributed to the unique porous and hollow structure, which provides a high density of active sites for the degradation of MB. Compared to LiNbO3, the improved photocatalytic performance of LiNb3O8 can be attributed to its layered structure type with the reduced symmetry enhancing the separation of electrons and holes.

Hydrothermal synthesis of In2O3 nanoparticles hybrid twins hexagonal disk ZnO heterostructures for enhanced photocatalytic activities and stability.

In2O3 nanoparticles hybrid twins hexagonal disk (THD) ZnO with different ratios were fabricated by a hydrothermal method. The as-obtained ZnO/In2O3 composites are constituted by hexagonal disks ZnO with diameters of about 1 µm and In2O3 nanoparticles with sizes of about 20-50 nm. With the increase of In2O3 content in ZnO/In2O3 composites, the absorption band edges of samples shifted from UV to visible light region. Compared with pure ZnO, the ZnO/In2O3 composites show enhanced photocatalytic activities for degradation of methyl orange (MO) and 4-nitrophenol (4-NP) under solar light irradiation. Due to suitable alignment of their energy band-gap structure of the In2O3 and ZnO, the formation of type п heterostructure can enhance efficient separation of photo-generate electro-hole pairs and provides convenient carrier transfer paths.

Hydrothermal-Assisted Sintering Strategy Towards Porous- and Hollow-Structured LiNb3O8 Anode Material.

Porous- and hollow-structured LiNb3O8 anode material was prepared by a hydrothermal-assisted sintering strategy for the first time. The phase evolution was studied, and the formation mechanism of the porous and hollow structure was proposed. The formation of the unique structure can be attributed to the local existence of liquid phase because of the volatilization of Li element. As the anode material, the initial discharge capacity is 285.1 mAhg-1 at 0.1 C, the largest discharge capacity reported so far for LiNb3O8. Even after 50 cycles, the reversible capacity can still maintain 77.6 mAhg-1 at 0.1 C, about 2.5 times of that of LiNb3O8 samples prepared by traditional solid-state methods. The significant improvement of Li storage capacity can be attributed to the special porous and hollow structure, which provides a high density of active sites and short parallel channels for fast intercalation of Li+ ions through the surface.

In situ polarization and dielectric property measurements of Pb(Zr0.52Ti0.48)O3 ferroelectric nanocrystals.

Pb(Zr0.52Ti0.48)O3/polycarbonate (PZT/PC) composite films with different concentration of PZT ferroelectric nanocrystals are prepared. The polarization and dielectric relaxation behavior of PZT ferroelectric nanocrystals are characterized using in situ transmittance and X-ray diffraction (XRD) measurements for the first time. It's found that 10% PZT/PC composite film has the largest orientation change and negligible dielectric relaxation after poling (the φ value of 13.8% is almost constant with time even for 168 h). Based on the XRD results, we consider that the preferential orientation of PZT nanocrystals to align in PC matrix after poling is [001] direction.

Ion-specific self-assembly of low-dimension aggregate structures of conjugated polymer at two-phase interface.

A novel and facile approach to manipulate the morphology of Cu(2+)-ion-specific assembly of conjugated polymer by coordinative interaction at an oil-water two-phase interface is present. The application of increasing importance is the use of π-conjugated polymers as receptors, exploiting their ability to selectively form complexes, which can obviously change the optical properties in solution and induce the formation of varied solid nano/microstructures. By this method, microtubes are formed through self-rolling of a strained ionic bilayer film at the oil/water interface.