Solubility of Hybrid Halide Perovskites in DMF and DMSO.

Solution methods remain the most popular means for the fabrication of hybrid halide perovskites. However, the solubility of hybrid perovskites has not yet been quantitively investigated. In this study, we present accurate solubility data for MAPbI3, FAPbI3, MAPbBr3 and FAPbBr3 in the two most widely used solvents, DMF and DMSO, and demonstrate huge differences in the solubility behavior depending on the solution compositions. By analyzing the donor numbers of the solvents and halide anions, we rationalize the differences in the solubility behavior of hybrid perovskites with various compositions, in order to take a step forward in the search for better processing conditions of hybrid perovskites for solar cells and optoelectronics.

New Acidic Precursor and Acetone-Based Solvent for Fast Perovskite Processing via Proton-Exchange Reaction with Methylamine.

A new solvent system for PbI2 based on HI solution in acetone with a low boiling point is proposed. High solubility of PbI2 is caused by the formation of iodoplumbate complexes, and reaches a concentration of 1.6 M. Upon its crystallization metastable solvate phases PbI2∙HI∙n{(CH3)2CO} are formed. The latter allows for their easy deposition on substrates in a form of smooth and uniform thin films by spin-coating. Through a fast acid-base reaction with a gaseous amine, the films of the intermediate phase can be completely converted to single-phase perovskite films. The developed method allows one to form smooth perovskite films with high crystallinity with a thickness up to 1 µm. Due to easy and fast processing, the developed method can be promising for perovskite technology upscaling.

Theoretical simulation and experimental design of selenium and gold incorporated polymer-based microcarriers for ROS-mediated combined photothermal therapy.

Recently, multi-modal combined photothermal therapy (PTT) with the use of photo-active materials has attracted significant attention for cancer treatment. However, drug carriers enabling efficient heating at the tumor site are yet to be designed: this is a fundamental requirement for broad implementation of PTT in clinics. In this work, we design and develop hybrid carriers based on multilayer capsules integrated with selenium nanoparticles (Se NPs) and gold nanorods (Au NRs) to realize reactive oxygen species (ROS)-mediated combined PTT. We show theoretically and experimentally that cooperative interaction of Se NPs with Au NRs improves the heat release efficiency of the developed capsules. In addition, after uptake by tumor cells, intracellular ROS level amplified by Se NPs inhibits the tumor growth. As a consequence, the synergy between Se NPs and Au NRs exhibits the advantages of hybrid carriers such as (i) improved photothermal conversion efficiency and (ii) dual-therapeutic effect. The results of in vitro and in vivo experiments demonstrate that the combination of ROS-mediated therapy and PTT has a higher tumor inhibition efficiency compared to the single-agent treatment (using only Se-loaded or Au-loaded capsules). Furthermore, the developed hybrid carriers show negligible in vivo toxicity towards major organs such as the heart, lungs, liver, kidneys and spleen. This study not only provides a potential strategy for the design of multifunctional "all-in-one" carriers, but also contributes to the development of combined PTT in clinical practice.

Iodine Solution Treatment in Nonpolar Solvents as a Facile Approach to Improve the Morphology and Photostability of Perovskite Films.

We propose a new, simple, and easily implemented approach to improve the morphology of thin films of lead halide perovskites. A key feature of the approach is the controllable size increase of perovskite grains facilitated by polyiodides formed on the surface of the perovskite upon its treatment with iodine solutions in nonpolar solvents with the best results obtained for iodine solution in toluene saturated with MAI. Such a treatment demonstrated an increase in the average grain size of the films of up to 3.5 times in approximately 2 min followed by significantly enhanced photostability.

Crystal structure of new formamidinium triiodide jointly refined by single-crystal XRD, Raman scattering spectroscopy and DFT assessment of hydrogen-bond network features.

A novel triiodide phase of the formamidinium cation, CH5N2 +·I3 -, crystallizes in the triclinic space group P at a temperature of 110 K. The structure consists of two independent isolated triiodide ions located on inversion centers. The centrosymmetric character of I3 - was additionally confirmed by the observed pronounced peaks of symmetrical oscillations of I3 - at 115-116 cm-1 in Raman scattering spectra. An additional structural feature is that each terminal iodine atom is connected with three neighboring planar formamidinium cations by N-H⋯I hydrogen bonding with the N-H⋯I bond length varying from 2.81 to 3.08 Å, forming a deformed two-dimensional framework of hydrogen bonds. A Mulliken population analysis showed that the calculated charges of hydrogen atoms correlate well with hydrogen-bond lengths. The crystal studied was refined as a three-component twin with domain ratios of 0.631 (1):0.211 (1):0.158 (1).

Methylammonium Polyiodides in Perovskite Photovoltaics: From Fundamentals to Applications.

Discovered in 2017, methylammonium polyiodides were proposed as a facile precursor for synthesis of hybrid perovskites by means of their interaction with metallic lead, which initiated further active exploration of their potential applications. Investigation of their unusual properties such as liquid state, unprecedented phase diversity and high reactivity revealed that methylammonium polyiodides are the first representatives of a new class of compounds-reactive polyhalide melts (RPM). In this review, we summarize the reported data on the unique properties of these compounds, discuss their potential for fabrication of hybrid perovskite films and describe the role of polyhalides in degradation of perovskite solar cells.

From Metallic Lead Films to Perovskite Solar Cells through Lead Conversion with Polyhalide Solutions.

Solutions of methylammonium and formamidinium polyhalides (AX1+n, A = MA, FA, X = I, Br) in isopropanol are introduced as novel versatile precursors for the fabrication of APbX3 hybrid perovskite thin films via oxidation of metallic Pb. The polyhalide solution with adjustable reactivity is distributed over a metallic Pb layer followed by iodine vapor postprocessing to tune the morphology and composition of the film using only the elements inherently present in the perovskite. This method is easily reproducible in any materials science laboratory with equipment commonly used for perovskite solar cell fabrication and resulted in power conversion efficiencies of 16.2 and 17.2% for planar solar cells using MAPbI3 and MA0.25FA0.75PbI2.75Br0.25 perovskites, respectively, as a proof of concept. Implementation of metallic lead thin films as the single Pb-containing precursors reduces a number of in-lab handling hazards compared to classical PbI2 powder and solutions and provides a variety of scalable deposition options.

Patterned films of a hybrid lead halide perovskite grown using space-confined conversion of metallic lead by reactive polyiodide melts.

A unique technique for preparation of thin patterned perovskite films is suggested based on an interaction of reactive polyiodide melts with metallic lead coatings using a patterned die with a given relief. The growth of perovskite in confined space results in pin-hole free textured films.

Methylammonium Polyiodides: Remarkable Phase Diversity of the Simplest and Low-Melting Alkylammonium Polyiodide System.

Newly discovered methylammonium polyiodides (MAIx) are unique precursors for innovative solvent-free technologies in perovskite photovoltaics because MAIx are liquids at room temperature and demonstrate high chemical reactivity. We investigated the features of an MAI-I2 system and built up a first phase diagram in wide temperature and composition ranges using data from differential scanning calorimetry, single-crystal X-ray diffraction, and visual thermal analysis. The phase diagram has been found to differ drastically from that of any related systems owing to the unique propensity of methylammonium toward forming a diversity of polyiodides with complicated crystal structures, namely, MAI2, MAI2.67, MAI4, and MAI5.5, found in this system for the first time. The performed density functional theory calculations revealed the crucial role of entropy contributing to the formation of higher methylammonium polyiodides, in good agreement with experimental data.

Strategic advantages of reactive polyiodide melts for scalable perovskite photovoltaics.

Despite tremendous progress in efficiency and stability, perovskite solar cells are still facing the challenge of upscaling. Here we present unique advantages of reactive polyiodide melts for solvent- and adduct-free reactionary fabrication of perovskite films exhibiting excellent quality over large areas. Our method employs a nanoscale layer of metallic Pb coated with stoichiometric amounts of CH3NH3I (MAI) or mixed CsI/MAI/NH2CHNH2I (FAI), subsequently exposed to iodine vapour. The instantly formed MAI3(L) or Cs(MA,FA)I3(L) polyiodide liquid converts the Pb layer into a pure perovskite film without byproducts or unreacted components at nearly room temperature. We demonstrate highly uniform and relatively large area MAPbI3 perovskite films, such as 100 cm2 on glass/fluorine-doped tin oxide (FTO) and 600 cm2 on flexible polyethylene terephthalate (PET)/indium tin oxide (ITO) substrates. As a proof-of-concept, we demonstrate solar cells with reverse scan power conversion efficiencies of 16.12% (planar MAPbI3), 17.18% (mesoscopic MAPbI3) and 16.89% (planar Cs0.05MA0.2FA0.75PbI3) in the standard FTO/c(m)-TiO2/perovskite/spiro-OMeTAD/Au architecture.

Formamidinium iodide: crystal structure and phase transitions.

At a temperature of 100 K, CH5N2+·I- (I), crystallizes in the monoclinic space group P21/c. The formamidinium cation adopts a planar symmetrical structure [the r.m.s. deviation is 0.002 Å, and the C-N bond lengths are 1.301 (7) and 1.309 (8) Å]. The iodide anion does not lie within the cation plane, but deviates from it by 0.643 (10) Å. The cation and anion of I form a tight ionic pair by a strong N-H⋯I hydrogen bond. In the crystal of I, the tight ionic pairs form hydrogen-bonded zigzag-like chains propagating toward [20-1] via strong N-H⋯I hydrogen bonds. The hydrogen-bonded chains are further packed in stacks along [100]. The thermal behaviour of I was studied by different physicochemical methods (thermogravimetry, differential scanning calorimetry and powder diffraction). Differential scanning calorimetry revealed three narrow endothermic peaks at 346, 387 and 525 K, and one broad endothermic peak at ∼605 K. The first and second peaks are related to solid-solid phase transitions, while the third and fourth peaks are attributed to the melting and decomposition of I. The enthalpies of the phase transitions at 346 and 387 K are estimated as 2.60 and 2.75 kJ mol-1, respectively. The X-ray powder diffraction data collected at different temperatures indicate the existence of I as the monoclinic (100-346 K), ortho-rhom-bic (346-387 K) and cubic (387-525 K) polymorphic modifications.