Abstract

　Development of fast and intuitive detection techniques for explosive vapors is highly desired for security applications. Among those techniques, fluorescence quenching has advantages in terms of portability and maintenance cost compared to electrically driven platforms. One of the challenging issues is the restricted sensitivity (i.e., low initial quenching and quenching saturation) caused by hindered diffusion of gaseous analytes inside a dense, solid film, and resulting limited surface area, where the target molecules are reacting. Here, multilevel 3D porous nanostructures are introduced, which possess strong fluorescence and enhanced sensing abilities, produced by a rapid and scalable lithographic technique. The cyanostilbene fluorophore with low-absorption around patterning wavelengths (≈355 nm) is newly designed to be incorporated into transparent photopolymer. The emission color and intensity of the composite films under excitation can be precisely controlled by adjusting the concentration of fluorophore based on intermolecular effects. The patterned, monolithic film with low-volume fraction (<40%) offers efficient diffusion paths inside a film and a large number of reaction sites for detecting gaseous analytes, enabling fast fluorescence quenching at an early stage (≈7.5 times higher than the solid film at 30 s) and fully suppressed fluorescence without quenching saturation, which cannot be achieved by conventional solid films.

Abstract

　Although perovskitesolarcells(PSCs)surpassing20%incerti-fied powerconversionefficiency(PCE) have beendemonstrat-ed with organichole-transportinglayers(HTLs), thermaldegra-dationremainsone of the key issuesfor practical applications.We fabricatedPSCs usinglow temperaturesolution-processedCuSCNas the inorganichole-transport layer(HTL),whichpos-sessesahighlystable crystalline structureand is robustevenat hightemperatures.Thebest-performingcell delivers aPCEof 18.0%, with15.9%measured at thestabilizedpoweroutput.Here we reportthe thermalstabilityof PSCsbasedonCuSCNin comparisonwithcommonly used2,2’,7,7’-tetrakis-(N,N-di-4-methoxyphenylamino)-9,9’-spirobifluorene(spiro-OMeTAD).The PSC fabricatedwithorganicspiro-OMeTAD de-gradesto 25%ofinitialPCE afterannealing for 2hat 1258Cinair under40%averagerelativehumidity.However,CuSCN-basedPSCsmaintainapproximately60%ofthe initialvalue,exhibitingsuperiorthermalstabilityunderidenticalconditions.Thisworkdemonstratesthathighefficiencyandimprovedthermalstability are simultaneouslyachievedwhenCuSCNisusedas an HTL in PSCs.

Abstract

　This work describes controlling charge transport properties of organic field-effect transistors (OFETs) with dicyanodistyrylbenzene-based organic semiconductors. Four fluorinated dicyanodistyrylbenzene derivatives (hTF1, hTF2, hTF3, and hTF5) with different degree of fluorination at the phenyl peripheries were synthesized and subjected to OFET devices. It was shown that the fluorination distinctly alters the polarity of charge transfer characteristics from p-type (hTF1), ambipolar (hTF2, hTF5), to n-type (hTF3). Systematic studies on photophysical, electrochemical, structural, and electronic properties revealed the fine tuning of the charge transport properties by the degree of fluorination. While p-type mobility of hTF1 was smaller than 0.01 cm2V−1 s−1, n-type mobility of hTF3 was as large as 0.7 cm2 V−1 s−1. On the other hand, well-balanced ambipolar mobilities were achieved for both hTF2 and hTF5 (hole and electron mobilities were virtually equal to be 0.07 cm2 V−1 s−1).

Abstract

　A novel nitronyl-nitroxide derivative for highly sensitive and selective detection of ascorbic acid (AA) is reported. The probe showed 260-fold fluorescence turn-on and diminished electron spin resonance (ESR) signal upon AA addition. The probe could detect AA over a broad concentration range from 1 μM to 2 mM and excellent selectivity over various antioxidants and acids through a combination of fluorescence and ESR responses, which originated from the dual-reactiveness of dual-quenching group nitronyl-nitroxide. We successfully demonstrated practical application potential of the probe by preparing nanoparticles and sensor papers and determining AA concentration in real samples including vitamin drinks and orange juices.

Abstract

　A long-standing dream in the large scale application of solar energy conversion is the fabrication of solar cells with high-efficiency and long-term stability at low cost. The realization of such practical goals depends on the architecture, process and key materials because solar cells are typically constructed from multilayer heterostructures of light harvesters, with electron and hole transporting layers as a major component. Recently, inorganic–organic hybrid lead halide perovskites have attracted significant attention as light absorbers for the fabrication of low-cost and high-efficiency solar cells via a solution process. This mainly stems from long-range ambipolar charge transport properties, low exciton binding energies, and suitable band gap tuning by managing the chemical composition. In our pioneering work, a new photovoltaic platform for efficient perovskite solar cells (PSCs) was proposed, which yielded a high power conversion efficiency (PCE) of 12%. The platform consisted of a pillared architecture of a three-dimensional nanocomposite of perovskites fully infiltrating mesoporous TiO2, resulting in the formation of continuous phases and perovskite domains overlaid with a polymeric hole conductor. Since then, the PCE of our PSCs has been rapidly increased from 3% to over 20% certified efficiency. The unprecedented increase in the PCE can be attributed to the effective integration of the advantageous attributes of the refined bicontinuous architecture, deposition process, and composition of perovskite materials. Specifically, the bicontinuous architectures used in the high efficiency comprise a layer of perovskite sandwiched between mesoporous metal–oxide layer, which is a very thinner than that of used in conventional dye-sensitized solar cells, and hole-conducting contact materials with a metal back contact. The mesoporous scaffold can affect the hysteresis under different scan direction in measurements of PSCs. The hysteresis also greatly depends on the cell architecture and perovskite composition. In this Account, we will describe what we do with major aspects including (1) the film morphology through the development of intermediate chemistry retarding the rapid reaction between methylammonium or formamidinium iodide and lead halide (PbI2) for improved perovskite film formation; (2) the phase stability and band gap tuning of the perovskite layer through the materials engineering; (3) the development of electron and hole transporting materials for carrier-selective contacting layers; and (4) the adoption of p–i–n and n–i–p architectures depending on the position of the electron or hole conducting layer in front of incident light. Finally, we will summarize the recent incredible achievements in PSCs, and finally provide challenges facing the future development and commercialization of PSCs.

Abstract

　To fabricate efficient formamidinium tin iodide (FASnI3) perovskite solar cells (PSCs), it is essential to deposit uniform and dense perovskite layers and reduce Sn4+ content. Here we used solvent-engineering and nonsolvent dripping process with SnF2 as an inhibitor of Sn4+. However, excess SnF2 induces phase separation on the surface of the perovskite film. In this work, we report the homogeneous dispersion of SnF2 via the formation of the SnF2–pyrazine complex. Consequently, we fabricated FASnI3 PSCs with high reproducibility, achieving a high power conversion efficiency of 4.8%. Furthermore, the encapsulated device showed a stable performance for over 100 days, maintaining 98% of its initial efficiency.

Abstract

　Beneficial effects are demonstrated by PbI2 incorporated into perovskite materials as a light absorber in solar cells. The PbI2 distributed into the perovskite layers leads to reduced hysteresis and ionic migration, and enables the fabrication of remarkably improved solar cells with a certified power conversion efficiency of 19.75% under air-mass 1.5 global (AM 1.5G) illumination of 100 mW cm−2 intensity.

Abstract

　The improved performance achieved by combining tert-butyl copper (II) phthalocyanine (CuPC) and po-spiro-OMeTAD as hole transporting material (HTM) for formamidinium lead iodide (FAPbI3)-based perovskite solar cells is reported. A device efficiency of 19.4% under standard 1 sun is obtained.

Abstract

　Highly transparent and nanostructured nickel oxide (NiO) films through pulsed laser deposition are introduced for efficient CH3NH3PbI3 perovskite solar cells. The (111)-oriented nanostructured NiO film plays a key role in extracting holes and preventing electron leakage as hole transporting material. The champion device exhibits a power conversion efficiency of 17.3% with a very high fill factor of 0.813.

Abstract

　Most efforts to grow superior films of organic-inorganic perovskites for solar cells have focused on methylammonium lead iodide (MAPbI3). However, formamidinium lead iodide (FAPbI3) has a broader solar absorption spectrum that could ultimately lead to better performance. Yang et al. grew high-quality FAPbI3 films by starting with a film of lead iodide and dimethylsulfoxide (DMSO) and then exchanging the DMSO with formamidinium iodide. Their best devices achieved power conversion efficiencies exceeding 20%.

Abstract

　Of the many materials and methodologies aimed at producing low-cost, efficient photovoltaic cells, inorganic–organic lead halide perovskite materials1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17 appear particularly promising for next-generation solar devices owing to their high power conversion efficiency. The highest efficiencies reported for perovskite solar cells so far have been obtained mainly with methylammonium lead halide materials1,2,3,4,5,6,7,8,9,10. Here we combine the promising—owing to its comparatively narrow bandgap—but relatively unstable formamidinium lead iodide (FAPbI3) with methylammonium lead bromide (MAPbBr3) as the light-harvesting unit in a bilayer solar-cell architecture13. We investigated phase stability, morphology of the perovskite layer, hysteresis in current–voltage characteristics, and overall performance as a function of chemical composition. Our results show that incorporation of MAPbBr3 into FAPbI3 stabilizes the perovskite phase of FAPbI3 and improves the power conversion efficiency of the solar cell to more than 18 per cent under a standard illumination of 100 milliwatts per square centimetre. These findings further emphasize the versatility and performance potential of inorganic–organic lead halide perovskite materials for photovoltaic applications.

Abstract

　Efficient metal-oxide-free perovskite solar cells were successfully developed by employing the N–I–P architecture. The modified solvent engineering process employing a diethylether drip as an orthogonal solvent enabled fabrication of a multi-layered device comprising FTO/PEI/PCBM/MAPbI3/PTAA/Au at low temperature (≤100 °C). Optimization of the thickness of the phenyl-C61-butyric acid methyl ester (PCBM) layer in the planar device yielded an overall power conversion efficiency (PCE) of 15.3% with a large hysteresis but a steady-state efficiency of 13.9% under AM 1.5G 100 mW cm−2 illumination. The use of the low-temperature processed dense-TiO2 layer in conjunction with the PCBM layer gave rise to performance comparable to that of the single electron transport layer (ETL) device and enabled fabrication of an efficient, flexible perovskite solar cell with a PCE of 11.1%.