A mechanochemical strategy for IRMOF assembly based on pre-designed oxo-zinc precursors.

We demonstrate a mechanochemical strategy that allowed the first successful mechanosynthesis of IRMOFs based on an oxo-centred secondary building unit (SBU). The presented study indicates that controlling the acid-base relationship between reagents is key to mechanochemical synthesis of IRMOFs, revealing a pre-assembled oxo-zinc amidate cluster as an efficient precursor for IRMOF mechanosynthesis.The authors would like to acknowledge the project operated within the Foundation for Polish Science Team Programme co-financed by the EU ‘‘European Regional Development Fund’’ TEAM/2011–7/8, and the European Union in the framework of Regional Development Fund through the Joint UW and WUT International PhD Program of Foundation for Polish Science – “Towards Advanced Functional Materials and Novel Devices” (MPD/2010/4) (D.P.) for financial support.This is the accepted manuscript. The final version was published in Chemical Communications and is available at http://pubs.rsc.org/en/Content/ArticleLanding/2015/CC/c4cc09917f#!divAbstract

Local Structure and Dynamics in Methylammonium, Formamidinium, and Cesium Tin(II) Mixed-Halide Perovskites from 119Sn Solid-State NMR.

Organic-inorganic tin(II) halide perovskites have emerged as promising alternatives to lead halide perovskites in optoelectronic applications. While they suffer from considerably poorer performance and stability in comparison to their lead analogues, their performance improvements have so far largely been driven by trial and error efforts due to a critical lack of methods to probe their atomic-level microstructure. Here, we identify the challenges and devise a 119Sn solid-state NMR protocol for the determination of the local structure of mixed-cation and mixed-halide tin(II) halide perovskites as well as their degradation products and related phases. We establish that the longitudinal relaxation of 119Sn can span 6 orders of magnitude in this class of compounds, which makes judicious choice of experimental NMR parameters essential for the reliable detection of various phases. We show that Cl/Br and I/Br mixed-halide perovskites form solid alloys in any ratio, while only limited mixing is possible for I/Cl compositions. We elucidate the degradation pathways of Cs-, MA-, and FA-based tin(II) halides and show that degradation leads to highly disordered, qualitatively similar products, regardless of the A-site cation and halide. We detect the presence of metallic tin among the degradation products, which we suggest could contribute to the previously reported high conductivities in tin(II) halide perovskites. 119Sn NMR chemical shifts are a sensitive probe of the halide coordination environment as well as of the A-site cation composition. Finally, we use variable-temperature multifield relaxation measurements to quantify ion dynamics in MASnBr3 and establish activation energies for motion and show that this motion leads to spontaneous halide homogenization at room temperature whenever two different pure-halide perovskites are put in physical contact

Halide Mixing and Phase Segregation in Cs2AgBiX6 (X=Cl, Br, I) Double Perovskites from Cesium-133 Solid-State NMR and Optical Spectroscopy

All-inorganic double perovskites (elpasolites) are a promising potential alternative to lead halide perovskite in optoelectronic applications. While halide mixing is a well-established strategy for band gap tuning, little is known about halide mixing and phase segregation phenomena in double perovskites. Here, we synthesize a wide range of single− and mixed−halide Cs2AgBiX6 (X=Cl, Br, I) double perovskites using mechanosynthesis and probe their atomic-level microstructure using 133Cs solid-state MAS NMR. We show that mixed Cl/Br materials form pure phases for any Cl/Br ratio while Cl/I and Br/I mixing is only possible with-in a narrow range of halide ratios (<3 mol% I) and leads to a complex mixture of products for higher ratios. We characterize the optical properties of the resulting materials and show that halide mixing does not lead to an appreciable tunability of the PL emission. We find that iodide incorporation is particularly pernicious in that it quenches the PL emission intensity and radiative charge carrier lifetimes for iodide ratios as low as 0.3 mol%. Our study shows that sol-id-state NMR, in conjunction with optical spectroscopies, provides a comprehensive understanding of the structure-activity relationships, halide mixing and phase segregation phenomena in Cs2AgBiX6 (X=Cl, Br, I) double perovskites

Molecular modification of spiro[fluorene-9,9′-xanthene]-based dopant-free hole transporting materials for perovskite solar cells

The molecular engineering of organic hole-transporting materials (HTMs) plays an important role in enhancing the performance and stability of perovskite solar cells (PSCs) as well as reducing their fabrication cost. Here, two low-cost spiro-OMeTAD analogues, namely SP-Naph and SP-SMe, featuring a spiro[fluorene-9,9-xanthene] (SFX) central core and asymmetric subunits are designed and synthesized. Specifically, the SFX core in the SP-Naph molecule is substituted with dimethoxyphenylnaphthylamine subunits to enhance conductivity and charge transport properties by expansion of the π-conjugated structure. On the other hand, in the molecular structure of SP-SMe, the methoxy groups (–OMe) from diphenylamine units were partially replaced with the methylsulfanyl groups (–SMe) to increase interaction with the perovskite surface through the “Lewis soft” S atoms. By combining various experimental and simulation methods, thestructure–property relationship of the newly synthesized HTMs was thoroughly investigated. The suitable HOMO energy level with the perovskite layer together with superior photoelectric properties and enhanced thermostability and humidity resistivity are obtained for the SP-SMe HTM. As a result, the planar n–i–p PSC with the dopant-free SP-SMe HTM yields a maximum power conversion efficiency (PCE) of 21.95%, which outperforms that with SP-Naph (20.51%) and doped spiro-OMeTAD (19.23%). Importantly, the device with SP-SMe also reveals enhanced operational stability under continuous 1 sun illumination and thermal stability at 65 °C. These findings provide valuable insight for the rational design of dopant-free organic HTMs based on the SFX core, which would promote the development of highly efficient and stable devices

Doping and phase segregation in Mn 2+ - and Co 2+ -doped lead halide perovskites from 133 Cs and 1 H NMR relaxation enhancement

Lead halide perovskites belong to a broad class of compounds with appealing optoelectronic and photovoltaic properties. Doping with transition metal ions such as Mn 2+ and Co 2+ has recently been reported to substantially enhance luminescence and stability of these materials. However, so far atomic-level evidence for incorporation of the dopants into perovskite phases has been missing. Here, we introduce a general and straightforward method for confirming the substitutional doping of bulk perovskite phases with paramagnetic dopants. Using 133 Cs and 1 H solid-state MAS NMR relaxation measurements we provide for the first time direct evidence that, consistent with current understanding, Mn 2+ is incorporated into the perovskite lattice of CsPbCl 3 and CsPbBr 3 and does not form clusters. We also show that, contrary to current conviction, Co 2+ is not incorporated into the perovskite lattice of MAPbI 3

Two-dimensional halide perovskite single crystals: principles and promises

Abstract In the last few years, two-dimensional (2D) metal halide perovskites (MHPs) are gaining tremendous attention and are replacing their three-dimensional (3D) congeners rapidly. These next-generation halide perovskites can circumvent the limitations of the 3D MHPs such as stability and structural diversity. The incorporation of bulky organic cation can not only prevent the moisture penetration into the crystal lattice and thus providing greater stability but also expands the field of hybrid semiconducting materials by offering structural diversity. These unique features render even higher tuneability and improved photophysical properties and as a result intensive investigations have been made for 2D MHP–based polycrystalline thin films. However, single crystals based on two-dimensional halide perovskites are still emerging and have great potential for future device applications. Along with the hybrid halide perovskites, the all inorganic halide perovskites are also blossoming. In this review, we have discussed exclusively the development of hybrid as well as all inorganic two-dimensional halide perovskites. First, we have discussed the crystal structure of 2D perovskites. In the next section, different growth procedures reported for preparation of single crystals are discussed. We then highlight the effect of doping on single crystals and their optoelectronic properties. Finally, we discuss the current challenges and future perspectives to further develop 2D single crystals for their efficient use in various devices