Ethylenediammonium diiodide (EDAI2) served as an effective additive for tin-based perovskite solar cells to attain a power conversion efficiency approaching 9%.

MASnI 3 ) PSC yielded device performance with PCE 5-6%, [9,10] but the devices were unstable and lacked reproducibility due to oxidation of Sn 2+ . To suppress that oxidation, much effort has been exerted to improve the enduring stability of the performance of tin-based PSC, [11][12][13][14][15][16] for example, through changing the electronic structure of perovskite, providing a uniform and close-packed film, introducing hydrogen bonding and a hydrophobic shell, and so forth. [12][13][14]17,18] Formamidinium (FA + ) is larger than MA + . FASnI 3 has a greater energy of formation of Sn vacancies because of weaker coupling between Sn and I; [19] FASnI 3 has thereby a smaller p-type conductivity than MASnI 3 and acts as a semiconductor. Wang et al. [18] studied the interaction of both FASnI 3 and MASnI 3 perovskites with water and concluded that these two cations affect the electronic structure of the oxygen-bonded perovskite lattice; FASnI 3 has a smaller rate of oxidation of Sn 2+ than MASnI 3 . They also suggested that stable Sn-based perovskite devices might be realized through an appropriate choice of organic cation to ensure effective protection against water penetration. [18] As a result, organic cation FA + has been used to make a FASnI 3 or hybrid FA + /MA + device with PCE 4-8%. [20] Moreover, applying large hydrophobic ammonium cations such as butylammonium (BA + ) or phenylethylammonium (PEA + ) within FASnI 3 to develop a quasi-2D [21] or hybrid 2D/3D [12,13,15] PSC was reported to make stable devices with PCE as great as 9.0%. [12] Beyond MA + and FA + , organic cation guanidinium (CH 6 N 3 + , GA), of size ≈278 pm [22] that is slightly larger than that of FA + (≈253 pm) [22] but has zero electric-dipolar moment, might be a suitable candidate for a tin-based PSC. [23,24] The empirical Goldschmidt tolerance factor of GASnI 3 is 1.051; GASnI 3 has a hexagonal geometry with crystal structures of two types, both with large bandgaps: 1.9 eV for the 3D hexagonal structure, space group P63/m, and 2.1 eV for the 2D monoclinic structure, space group P21/n, near 296 K. [25] We applied organic cation precursor GAI mixed with FAI in varied proportions with equimolar SnI 2 precursor in the presence of SnF 2 and ethylenediammonium diiodide (EDAI 2 ) as additives to enhance both the photovoltaic performance and the enduring stability of a tin-based perovskite. As demonstrated at the top of Figure 1, we prepared the tin perovskites according to stoichiometric ratios of their precursors; these prepared perovskites conform to a general expression, The stability of a tin-based perovskite solar cell is a major challenge. Here, hybrid tin-based perovskite solar cells in a new series that incorporate a nonpolar organic cation, guanidinium (GA + ), in varied proportions into the formamidinium (FA + ) tin triiodide perovskite (FASnI 3 ) crystal structure in the presence of 1% ethylenediammonium diiodide (EDAI 2 ) as an additive, are reported. The device performance is optimized at a precursor ratio (GAI:FAI) of 20:80 to atta...

We report here a series of nontoxic and stable bismuth-based perovskite nanocrystals (PeNCs) with applications for photocatalytic reduction of carbon dioxide to methane and carbon monoxide. Three bismuth-based PeNCs of general chemical formulas A 3 Bi 2 I 9 , in which cation A + = Rb + or Cs + or CH 3 NH 3 + (MA + ), were synthesized with a novel ultrasonication top-down method. PeNC of Cs 3 Bi 2 I 9 had the best photocatalytic activity for the reduction of CO 2 at the gas−solid interface with formation yields 14.9 μmol g −1 of methane and 77.6 μmol g −1 of CO, representing a much more effective catalyst than TiO 2 (P25) under the same experimental conditions. The products of the photocatalytic reactions were analyzed using a gas chromatograph coupled with a mass spectrometer. According to electron paramagnetic resonance and diffuse-reflectance infrared spectra, we propose a reaction mechanism for photoreduction of CO 2 via Bi-based PeNC photocatalysts to form CO, CH 4 , and other possible side products.

2850 wileyonlinelibrary.com large amounts of liquids and are excellent fi lters. Sponges with a volume of 1000 cm 3 can process up to 3000 L water h −1 . Furthermore, they can conduct light as discovered recently by Brümmer et al. [ 2 ] In addition, Natalio et al. reported on the formation of sponge skeletons shown to feature great bending strength and on the role of silicatein-α in the biomineralization of silicates in sponges, which accounts for the high reversible compressibility of sponges in spite of low densities. [ 3 ] Aizenberg et al. pointed out on the example of the so-called glass sponges ( Euplectella ) the important role of the hierarchical design from the nanometer to macroscopic length scale for structural materials. [ 4 ] The structural base of sponges are multiarmed spicules of silicate or calcium carbonate, which form highly porous structures of several hierarchical layers as shown in Figure 1 A,B. This leads to highly porous ultralight 3D materials (ultralight is defi ned when the density of material is <10 mg cm −3 ).[ 5 ] In recent literature, a variety of highly porous ultralight 3D materials were reported based on carbon, ceramics, and cellulose, which were characterized by porosities >99% and relatively high compressive strength. [6][7][8][9][10] Carbon and cellulose based sponges show ultralow densities and excellent mechanical properties but soft sponges with similar mechanical integrity are missing.Since spicules of natural sponges conspicuously resemble polymer fi bers, formation of such fi brous structures by electrospinning [ 11 ] could be a promising concept for the preparation of polymer-based biomimetic analogous of natural sponges and would open the huge potential of electrospun materials for 3D sponge-type structures. Indeed, 3D porous structures were prepared by electrospinning which was nicely summarized in comprehensive review in recent literature. [ 7 ] However, previous efforts of making 3D highly porous electrospun materials, for example, via ultrasonic treatment, resulted in higher densities and correspondingly lower porosities of <99%, [ 12 ] as well as relatively poor mechanical performance. Remarkably, Eichhorn et al. claimed that theoretically ultrahigh porosities of electrospun nonwovens >99% could not be achieved. [ 13 ] In contrast to these reports, we present here the formation of ultralight weight highly porous 3D electrospun polymer fi ber-based spongy structures with densities as low as 2.7 mg cm −3 corresponding to a porosity of 99.6%. They were prepared by electrospinning of a photo cross-linkable polymer followed by UV cross-linking, mechanical cutting, suspending cut fi bers in liquid dispersion, and freezedrying. These polymer sponges showed in analogy to natural Ultralight, Soft Polymer Sponges by Self-Assembly of Short Electrospun Fibers in Colloidal DispersionsGaigai Duan , Shaohua Jiang , Valérie Jérôme , Joachim H. Wendorff , Amir Fathi , Jaqueline Uhm , Volker Altstädt , Markus Herling , Josef Breu , Ruth Freitag , Seema Agarwal , and Andreas Gre...

The excitonic relaxation dynamics of perovskite adsorbed on mesoporous thin films of Al2O3 and NiO upon excitation at 450 nm were investigated with femtosecond optical gating of photoluminescence (PL) via up-conversion. The temporal profiles of emission observed in spectral region 670-810 nm were described satisfactorily with a composite consecutive kinetic model and three transient components representing one hot and two cold excitonic relaxations. All observed relaxation dynamics depend on the emission wavelength, showing a systematic time-amplitude correlation for all three components. When the NiO film was employed, we observed an extent of relaxation proceeding through the non-emissive surface state larger than through the direct electronic relaxation channel, which quenches the PL intensity more effectively than on the Al2O3 film. We conclude that perovskite is an effective hole carrier in a p-type electrode for NiO-based perovskite solar cells showing great performance.