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N-Methyl-2-hydroxy-1-ethanaminium lead iodide exhibits a low melting temperature (Tm = 99 °C) among 2D hybrid metal halides (HMHs). This discovery expands the low melting characteristics of 2D HMHs to include a stepped 9R-like structure, suggesting significant potential for melt-processing and hybrid glass formation. [ABSTRACT FROM AUTHOR]

Herein, we demonstrated the unique advantage of a mechanochemical reaction to prepare a salt with hard and soft acid and base ions concurrently by solution synthesis owing to the soft acid preferring to combine with the soft base and vice versa. We prepared Bu4N1−xLixMnxPb1−xI3 (x = 0.011−0.14) by mechanochemical synthesis. The doping induced a structural phase transition at ∼342 K and much enhancement of ionic conduction above 342 K for all co-doped hybrids regarding Bu4NPbI3 because of the voids around the Mn2+/Li+ ions by doping. [ABSTRACT FROM AUTHOR]

PbI2 films as templates are essential to the quality of perovskite (PVK) film in a two-step sequential deposition process. Herein, we demonstrate that PbI2 microcrystal powder (P-PbI2) of micrometer size is beneficial for preparing higher-quality PbI2 films in contrast to millimeter-sized PbI2 crystals (C-PbI2) under low relative humidity (RH) conditions. Surprisingly, C-PbI2 allowed the growth of denser films than P-PbI2 under heavy RH conditions. Ultimately, P-PbI2 gave PVK solar cells (PSCs) a best power conversion efficiency (PCE) of 23.30% under a low RH of 30 ± 5%, and C-PbI2 derived an impressive PCE of 21.09% when fabricated under conditions with RH = 50 ± 5%. This work provides ideas for the selection of lead iodide for the fabrication of PSCs under air conditions. [ABSTRACT FROM AUTHOR]

The supramolecular lead iodide perovskite crystals, {[NH4(18-crown-6)]PbI3}∞ (1), (18-crown-6 = 1,4,7,10,13,16-hexaoxacyclooctadecane), was successfully achieved by a facile solvent evaporation strategy using a DMF solution containing equal molar quantities of PbI2, NH4I and 18-crown-6. The supramolecular perovskite was characterized by microanalysis for C, H and N elements, thermogravimetric (TG) analysis, differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD) and single crystal X-ray diffraction techniques. DSC measurements demonstrated that 1 experiences a two-step thermotropic phase transition around 333 K and 383 K, respectively. The phase transition is relevant to the disorder–order transformation of the 18-crown-6 molecule at ∼333 K, while both breaking-symmetry and ordered-disordered transformation of the 18-crown-6 molecule occurred at ∼383 K. In addition, the sharp change of the PbI6 coordination octahedron distortion degree plays a synergistic role in the two-step phase transition. The dielectric relaxation occurs above 243 K in 1 and is mainly attributed to the displacement of the NH4+ ions relative to the ring of the 18-crown-6 molecule and {PbI3}∞ chain induced by an AC electrical field. [ABSTRACT FROM AUTHOR]

The supramolecular lead iodide perovskite crystals, {[NH4(18-crown-6)]PbI3}∞ (1), (18-crown-6 = 1,4,7,10,13,16-hexaoxacyclooctadecane), was successfully achieved by a facile solvent evaporation strategy using a DMF solution containing equal molar quantities of PbI2, NH4I and 18-crown-6. The supramolecular perovskite was characterized by microanalysis for C, H and N elements, thermogravimetric (TG) analysis, differential scanning calorimetry (DSC), powder X-ray diffraction (PXRD) and single crystal X-ray diffraction techniques. DSC measurements demonstrated that 1 experiences a two-step thermotropic phase transition around 333 K and 383 K, respectively. The phase transition is relevant to the disorder–order transformation of the 18-crown-6 molecule at ∼333 K, while both breaking-symmetry and ordered-disordered transformation of the 18-crown-6 molecule occurred at ∼383 K. In addition, the sharp change of the PbI6 coordination octahedron distortion degree plays a synergistic role in the two-step phase transition. The dielectric relaxation occurs above 243 K in 1 and is mainly attributed to the displacement of the NH4+ ions relative to the ring of the 18-crown-6 molecule and {PbI3}∞ chain induced by an AC electrical field. [ABSTRACT FROM AUTHOR]

Interfaces composed of three-dimensional (3D) and 2D organic–inorganic hybrid formamidinium lead iodide (FAPbI3) linked by organic spacers (OSs) are studied using first-principles calculations. The OS cations with aromatic rings, like phenylethylammonium and anilinium (AN), are found to be more favourable for enhancing the stability of the 3D/2D interface than butylammonium with aliphatic chains. The AN-based interface shows the highest resistance to penetration of water molecules. [ABSTRACT FROM AUTHOR]

The dissolution of lead iodide (PbI2) is very important for the purpose of avoiding environmental pollution. Here, an environmentally benign polyethylene glycol-based deep eutectic solvent (PEGylated DES) has been found to dissolve PbI2 with a 54.35% mass fraction at room temperature (25 °C), which is 716.1 times that in water (0.0759% mass fraction) at similar conditions. Furthermore, the dissolved PbI2 could be simply recycled by the addition of water as an antisolvent at room temperature. This work provides a green method for the recycling of toxic PbI2 with high performance at mild conditions. [ABSTRACT FROM AUTHOR]

The introduction of chirality in layered hybrid perovskites breaks the symmetry of their inorganic sub-lattices. Consequently, they show intriguing linear and non-linear optical properties. Here we explore the effect of chirality on the excitonic photoluminescence of chiral (R- and S-α-MBA)2PbI4 (MBA: methylbenzylammonium) at cryogenic temperatures. The induced chirality splits the excitonic emissions below 150 K. Additionally, (R- and S-α-MBA)2PbI4 show wavelength-tunable second harmonic generation (SHG) that depends strongly on the polarization angle of the incident light. [ABSTRACT FROM AUTHOR]

A salicylaldehyde Schiff base hybrid lead iodide perovskite [SAPD]PbI3 (SAPD = 1-((2-hydroxybenzylidene)amino)pyridin-1-ium) was found to show a robust nonlinear optical response and large spontaneous polarization. We expect this work to inspire researchers to investigate the optical control of ferroelectricity in hybrid perovskites. [ABSTRACT FROM AUTHOR]

The high mobility of charge carriers in graphene (G) together with the ease of processing and tunable optical properties of colloidal quantum dots (CQD) has provided high-performance hybrids for the next generation of phototransistors. In order to get a higher quality film of PbS QDs, understanding the effect of the ligand exchange method is critical. So, to improve the interdot electronic coupling, we propose a new conducting ligand to prepare a dense and self-assembled active layer of FAPbI3–PbS quantum dots on G/Si/SiO2 substrates. Quantum dot (QD) nanocrystalline films were prepared via two different procedures: liquid phase ligand exchange (LPE) and solid phase ligand exchange (SPE). SPE with formamidinium lead iodide significantly increases the packing density and surface coverage of the active layer on the graphene substrate. Efficient light absorption in the near IR region and reduced charge transport resistance in the QD film are demonstrated. The SPE fabricated graphene-based heterostructure phototransistors exhibit improved specific detectivity (by 34%) and ION/IOFF ratio (by 23%) as compared with LPE. Our findings pave a way to develop high-throughout graphene-based phototransistors based on FAPbI3-CQDs. [ABSTRACT FROM AUTHOR]

Introducing electronically active organic components into lower dimensional metal halide compounds is an effective strategy to improve the electronic properties of hybrid metal halide materials. We have previously used this strategy to explore hybrid halides with tetrathiafulvalenes (TTFs) and a series of lead iodides and bismuth halides were isolated. The electronic properties were improved notably using this modification. In this work, we expand the study of TTF based main-group metal halides to double metal halides with mixed lead and copper transition metals. Two hybrid TTF–lead–cuprous iodides, formulated as [TTF]5[Pb2Cu2I10]·H2O (1) and [TTF]2[PbCu2I6] (2), and two monometal analogues of [TTF]2[Cu4I6]·H2O (3) and [TTF]2[Ag4I6] (4) were crystallographically characterized. The anion of 1 is a 0D cluster, while that of the others is a 1D chain structure. The anion structures of 1–4 are novel and are reported for the first time. The TTF moieties are stacked to form a 2D framework in 1 and 1D columns in 2–4. We found that the semiconductor properties of the hybrids are related to electron donation from an anion to a cation. The electronic state of the TTF cations is another significant factor that affects the electronic properties of the materials. More notably, this work proved that the conductivity and photoconductivity of the mixed metal iodides are superior to those of the monometal iodides. [ABSTRACT FROM AUTHOR]

Solar perovskites have received phenomenal attention and success over the past decade, due to their high power conversion efficiencies (PCE), ease of fabrication and low cost which has enabled the prospect of them being a real commercial contender to the traditional silicon technology. In one of the several developments on the archetypal MAPbI3 perovskite absorber layer, FAPbI3 was found to obtain a higher PCE, likely due to its more optimum band gap, with doping strategies focusing on the inclusion of MA+/Cs+ cations to avoid the unfavourable phase transformation to a photoinactive phase. To better understand the phase change from the photoactive cubic (Pm3¯m) black (α) phase to the unwanted photoinactive (P63/mmc) yellow (δ) phase, we make use of variable temperature Raman spectroscopy to probe the molecular species and its relationship to the inorganic framework. We show for the first time there to be no Raman active modes for the α phase up to 4000 cm−1, which can be correlated to the Pm3¯m cubic symmetry of that phase. Our detailed studies suggest that previous reports of the observation of Raman peaks for this phase are likely associated with degradation reactions from the localised laser exposure and the formation of Raman active lead oxide. In addition, we have identified water as a contributing factor to the transformation, and observed a corresponding signal in the Raman spectra, although confirmation of its exact role still remains inconclusive. [ABSTRACT FROM AUTHOR]

Solar perovskites have received phenomenal attention and success over the past decade, due to their high power conversion efficiencies (PCE), ease of fabrication and low cost which has enabled the prospect of them being a real commercial contender to the traditional silicon technology. In one of the several developments on the archetypal MAPbI3 perovskite absorber layer, FAPbI3 was found to obtain a higher PCE, likely due to its more optimum band gap, with doping strategies focusing on the inclusion of MA+/Cs+ cations to avoid the unfavourable phase transformation to a photoinactive phase. To better understand the phase change from the photoactive cubic (Pm3¯m) black (α) phase to the unwanted photoinactive (P63/mmc) yellow (δ) phase, we make use of variable temperature Raman spectroscopy to probe the molecular species and its relationship to the inorganic framework. We show for the first time there to be no Raman active modes for the α phase up to 4000 cm−1, which can be correlated to the Pm3¯m cubic symmetry of that phase. Our detailed studies suggest that previous reports of the observation of Raman peaks for this phase are likely associated with degradation reactions from the localised laser exposure and the formation of Raman active lead oxide. In addition, we have identified water as a contributing factor to the transformation, and observed a corresponding signal in the Raman spectra, although confirmation of its exact role still remains inconclusive. [ABSTRACT FROM AUTHOR]

In this work, we demonstrate that 1D EDPbI4 crystals containing face-sharing PbI64− octahedra are synthesized using ethylenediammonium (ED) as an organic cation in hydroiodic acid. However, by the addition of hydrochloric acid to the synthetic solution, 2D [(ED)2PbI4]Cl2 crystals are interestingly constructed without substitution of iodides by chlorides. The importance of chloride ions in the structure has been revealed by employing the single-crystal X-ray diffraction technique. Isolated chlorides, through forming hydrogen bonds with ammonium groups and creating (ED)2Cl22+ templating layers, lessen the interplays between organic cations and inorganic units and consequently lead to the formation of almost undistorted PbI42− perovskite layers. The band gaps of the resultant crystals have been determined to be 2.72 eV and 2.30 eV for EDPbI4 and [(ED)2PbI4]Cl2, respectively. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) measurements indicate that both compounds are thermally stable up to 250 °C without any phase transition. [ABSTRACT FROM AUTHOR]

Numerous reports have been made in the literature on the usability of a halide perovskite, namely methyl ammonium lead iodide (CH3NH3PbI3), as a light harvesting material. Suitable optimization in material composition and synthesis has led to an improvement in device performance. However, the susceptibility of CH3NH3PbI3 towards atmospheric water is an alarming issue which hinders its long-term application in day-to-day life. Herein, low temperature synthesized V2O5 nanorods are incorporated into the CH3NH3PbI3 matrix to facilitate carrier dynamics by interface engineering. The optimized hybrid sample exhibits a much improved and stable photo-response behaviour than the pristine building blocks. Additionally, the modified perovskite shows improved hydrophobicity in the form of small-scale surface undulations due to the incorporation of V2O5 nanorods into it. This way, we have solved two problems with one single action, firstly by improving the device performance and secondly by stabilizing the sample against ambient water species. [ABSTRACT FROM AUTHOR]

A new lead borate iodide, [O2Pb3]2(BO3)I, has been successfully synthesized by a facile hydrothermal reaction. It exhibits an infinite one-dimensional (1D) 1∞ [O2Pb3] double chain which is constructed from OPb4 oxygen-centered tetrahedra. The 1∞ [O2Pb3] double chains are further bridged by BO3 units via sharing oxygen atoms to form two-dimensional (2D) 2∞ [(O2Pb3)2(BO3)] layers with the I− ions situated in the spaces between the layers. First principles calculations indicate that [O2Pb3]2(BO3)I exhibits a birefringence of about 0.072@1064 nm which originates from the synergistic contributions of the Pb–O/I and BO3 units. The IR, UV-vis-NIR and EDS results, as well as TG-DSC curves were also discussed in detail. [ABSTRACT FROM AUTHOR]

A novel black organoammonium iodoplumbate semiconductor, namely phenyl viologen lead iodide C22H18N2(PbI3)2 (PhVPI), was successfully synthesized and characterized. This material showed physical and chemical properties suitable for photovoltaic applications. Indeed, low direct allowed band gap energy (Eg = 1.32 eV) and high thermal stability (up to at least 300 °C) compared to methylammonium lead iodide CH3NH3PbI3 (MAPI, Eg = 1.5 eV) render PhVPI potentially attractive for solar cell fabrication. The compound was extensively characterized by means of X-ray diffraction (performed on both powder and single crystals), UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS), UV-photoelectron spectroscopy (UPS), FT-IR spectroscopy, TG-DTA, and CHNS analysis. Reactivity towards water was monitored through X-ray powder diffraction carried out after prolonged immersion of the material in water at room temperature. Unlike its methyl ammonium counterpart, PhVPI proved to be unaffected by water exposure. The lack of reactivity towards water is to be attributed to the quaternary nature of the nitrogen atoms of the phenyl viologen units that prevents the formation of acid–base equilibria when in contact with water. On the other hand, PhVPI's thermal stability was evaluated by temperature-controlled powder XRD measurements following an hour-long isothermal treatment at 250 and 300 °C. In both cases no signs of decomposition could be detected. However, the compound melted incongruently at 332 °C producing, upon cooling, a mostly amorphous material. PhVPI was found to be slightly soluble in DMF (∼5 mM) and highly soluble in DMSO. Nevertheless, its solubility in DMF can be dramatically increased by adding an equimolar amount of DMSO. Therefore, phenyl viologen lead iodide can be amenable for the fabrication of solar devices by spin coating as actually done for MAPI-based cells. The crystal structure, determined by means of single crystal X-ray diffraction using synchrotron radiation, turned out to be triclinic and consequently differs from the prototypal perovskite structure. In fact, it comprises infinite double chains of corner-sharing PbI6 octahedra along the a-axis direction with phenyl viologen cations positioned between the columns. Finally, the present determination of PhVPI's electronic band structure achieved through UPS and UV-Vis DRS is instrumental in using the material for solar cells. [ABSTRACT FROM AUTHOR]

A novel black organoammonium iodoplumbate semiconductor, namely phenyl viologen lead iodide C22H18N2(PbI3)2 (PhVPI), was successfully synthesized and characterized. This material showed physical and chemical properties suitable for photovoltaic applications. Indeed, low direct allowed band gap energy (Eg = 1.32 eV) and high thermal stability (up to at least 300 °C) compared to methylammonium lead iodide CH3NH3PbI3 (MAPI, Eg = 1.5 eV) render PhVPI potentially attractive for solar cell fabrication. The compound was extensively characterized by means of X-ray diffraction (performed on both powder and single crystals), UV-Vis diffuse reflectance spectroscopy (UV-Vis DRS), UV-photoelectron spectroscopy (UPS), FT-IR spectroscopy, TG-DTA, and CHNS analysis. Reactivity towards water was monitored through X-ray powder diffraction carried out after prolonged immersion of the material in water at room temperature. Unlike its methyl ammonium counterpart, PhVPI proved to be unaffected by water exposure. The lack of reactivity towards water is to be attributed to the quaternary nature of the nitrogen atoms of the phenyl viologen units that prevents the formation of acid–base equilibria when in contact with water. On the other hand, PhVPI's thermal stability was evaluated by temperature-controlled powder XRD measurements following an hour-long isothermal treatment at 250 and 300 °C. In both cases no signs of decomposition could be detected. However, the compound melted incongruently at 332 °C producing, upon cooling, a mostly amorphous material. PhVPI was found to be slightly soluble in DMF (∼5 mM) and highly soluble in DMSO. Nevertheless, its solubility in DMF can be dramatically increased by adding an equimolar amount of DMSO. Therefore, phenyl viologen lead iodide can be amenable for the fabrication of solar devices by spin coating as actually done for MAPI-based cells. The crystal structure, determined by means of single crystal X-ray diffraction using synchrotron radiation, turned out to be triclinic and consequently differs from the prototypal perovskite structure. In fact, it comprises infinite double chains of corner-sharing PbI6 octahedra along the a-axis direction with phenyl viologen cations positioned between the columns. Finally, the present determination of PhVPI's electronic band structure achieved through UPS and UV-Vis DRS is instrumental in using the material for solar cells. [ABSTRACT FROM AUTHOR]

The poorly conductive organic layers in two-dimensional (2D) perovskites create quantum wells, which hinder the carrier separation and transformation. Therefore, the search for new 2D hybrid lead-halide materials with conductive organic components is crucial to high performance 2D perovskite solar cells. Tetrathiafulvalene (TTF) and its derivatives are well-known building blocks for conductive organic materials. We report here a new compound containing TMT–TTF (tetrakis(methylthio)tetrathiafulvalene) and layered PbI2, formulated as (TMT–TTF)[Pb2.6/3□0.4/3I2]3 (1). Crystal structural analysis shows that compound 1 is a unique TMT–TTF-intercalated 2D hybrid lead iodide with partially oxidized TMT–TTF cations and Pb-vacancy in anion. Its structural characteristics give the compound a narrow band gap and high conductivity. Furthermore, the carrier density and the photoelectric properties are first evaluated for TTF-PbI compounds and the results show that these properties of 1 are superior to those of the previously reported TTF-PbI salt, which is attractive for exploiting new lead-halide materials. [ABSTRACT FROM AUTHOR]

A new hybrid lead iodide material (HP1) having 4-vinylphenylene ammonium as the organic cation has been prepared. The structural formula based on chemical analysis of HP1 corresponds to PbI2.5(4-styrylammonium)0.5. The crystallinity of HP1 was confirmed by powder X-ray diffraction and high resolution transmission electron microscopy. The presence of the styryl ammonium moiety in HP1 allows post-synthetic modification by radical copolymerization with styrene to obtain the HP2 material with higher hydrophobicity. Stability tests reveal that both HP1 and HP2 show hydrogen evolution in the dark, indicating about 0.6% partial decomposition of the hybrid material. This hydrogen evolution increases by a factor of 3 when HP1 and HP2 are exposed to visible light. X-ray photoelectron spectroscopy analysis shows an increase of NH2 groups and a decrease of NH3+ units suggesting that the origin of hydrogen evolution is the deprotonation of ammonium ions. [ABSTRACT FROM AUTHOR]

Yellow transparent single crystals of the new compound K2Pb(OCN)I3 were synthesized from a mixture of lead iodide and potassium cyanate through a solid-state reaction, which was controlled by the differential scanning calorimetry (DSC) technique. The single crystal X-ray refinement showed that K2Pb(OCN)I3 crystallizes in the cubic system (Fd3¯m, a = 16.295(2) Å, V = 4327(1) Å3, Z = 16 and R1 = 0.0167). The structure is basically composed of two frameworks built from potassium tetrahedra capped by OCN− units and corner-sharing lead iodide octahedra. The infrared spectrum of K2Pb(OCN)I3 reveals the presence of vibration modes that were assigned to cyanate ions. The band structure and total and partial density of states calculated by DFT with the PBE functional (CASTEP code) showed that this compound exhibits a direct band gap of 2.19 eV, which is in good agreement with the experimental value obtained from a diffuse reflectance measurement (2.4 eV). The investigation of the electrical properties of this material demonstrates that it is highly resistive and has large permittivity (relative values of up to 104 at 150 °C). However, it does not display ferroelectric behavior. [ABSTRACT FROM AUTHOR]

Yellow transparent single crystals of the new compound K2Pb(OCN)I3 were synthesized from a mixture of lead iodide and potassium cyanate through a solid-state reaction, which was controlled by the differential scanning calorimetry (DSC) technique. The single crystal X-ray refinement showed that K2Pb(OCN)I3 crystallizes in the cubic system (Fd3¯m, a = 16.295(2) Å, V = 4327(1) Å3, Z = 16 and R1 = 0.0167). The structure is basically composed of two frameworks built from potassium tetrahedra capped by OCN− units and corner-sharing lead iodide octahedra. The infrared spectrum of K2Pb(OCN)I3 reveals the presence of vibration modes that were assigned to cyanate ions. The band structure and total and partial density of states calculated by DFT with the PBE functional (CASTEP code) showed that this compound exhibits a direct band gap of 2.19 eV, which is in good agreement with the experimental value obtained from a diffuse reflectance measurement (2.4 eV). The investigation of the electrical properties of this material demonstrates that it is highly resistive and has large permittivity (relative values of up to 104 at 150 °C). However, it does not display ferroelectric behavior. [ABSTRACT FROM AUTHOR]

The synthesis of hydroxylammonium lead iodide NH3OHPbI3 was accomplished by means of the reaction between water solutions of HI and NH2OH with PbI2 in sulfolane in conjunction with either crystallization by CH2Cl2 vapor diffusion or sulfolane extraction with toluene. The appropriate choice of the solvent was found to be crucial in order to attain the desired material. The synthesized compound was extensively characterized by single crystal and powder X-ray diffraction, UV-Vis diffuse reflectance spectroscopy, FT-IR spectroscopy, 1H-NMR spectroscopy, TG-DTA-QMS EGA (Evolved Gas Analysis), ESI-MS, and CHNS analysis. NH3OHPbI3 is an extremely reactive, deliquescent solid that easily oxidizes in air releasing iodine. Furthermore, it is the first reported perovskite to melt (m.p. around 80 °C) before decomposing exothermally at 103 °C. Such a chemical behavior, together with its optical absorption properties (i.e. yellow-colored perovskite), renders this material totally unsuitable for photovoltaic applications. The deliquescence of the material is to be ascribed to the strong hydrophilicity of hydroxylammonium ion. On the other hand, the relatively high Brønsted acidity of hydroxylammonium (pKa = 5.97) compared to other ammonium cations, promotes the reduction of atmospheric oxygen to water and the NH3OHPbI3 oxidation. The crystal structure, determined by single crystal X-ray diffraction with synchrotron radiation, is orthorhombic, but differs from the prototypal perovskite structure. Indeed it comprises infinite chains of face-sharing PbI6 octahedra along the c-axis direction with hydroxylammonium cations positioned between the columns, forming layers on the ac plane. The solvent intercalates easily between the layers. The crystal structure is apparently anomalous considering that the expected Goldschmidt's tolerance factor for the system (0.909) lies in the range of a stable prototypal perovskite structure. Therefore, the strong hydrogen bond forming tendency of hydroxylamine is likely to account for the apparent structural anomaly. [ABSTRACT FROM AUTHOR]

The synthesis of hydroxylammonium lead iodide NH3OHPbI3 was accomplished by means of the reaction between water solutions of HI and NH2OH with PbI2 in sulfolane in conjunction with either crystallization by CH2Cl2 vapor diffusion or sulfolane extraction with toluene. The appropriate choice of the solvent was found to be crucial in order to attain the desired material. The synthesized compound was extensively characterized by single crystal and powder X-ray diffraction, UV-Vis diffuse reflectance spectroscopy, FT-IR spectroscopy, 1H-NMR spectroscopy, TG-DTA-QMS EGA (Evolved Gas Analysis), ESI-MS, and CHNS analysis. NH3OHPbI3 is an extremely reactive, deliquescent solid that easily oxidizes in air releasing iodine. Furthermore, it is the first reported perovskite to melt (m.p. around 80 °C) before decomposing exothermally at 103 °C. Such a chemical behavior, together with its optical absorption properties (i.e. yellow-colored perovskite), renders this material totally unsuitable for photovoltaic applications. The deliquescence of the material is to be ascribed to the strong hydrophilicity of hydroxylammonium ion. On the other hand, the relatively high Brønsted acidity of hydroxylammonium (pKa = 5.97) compared to other ammonium cations, promotes the reduction of atmospheric oxygen to water and the NH3OHPbI3 oxidation. The crystal structure, determined by single crystal X-ray diffraction with synchrotron radiation, is orthorhombic, but differs from the prototypal perovskite structure. Indeed it comprises infinite chains of face-sharing PbI6 octahedra along the c-axis direction with hydroxylammonium cations positioned between the columns, forming layers on the ac plane. The solvent intercalates easily between the layers. The crystal structure is apparently anomalous considering that the expected Goldschmidt's tolerance factor for the system (0.909) lies in the range of a stable prototypal perovskite structure. Therefore, the strong hydrogen bond forming tendency of hydroxylamine is likely to account for the apparent structural anomaly. [ABSTRACT FROM AUTHOR]

A recent model of iodide-ion conduction in methylammonium lead iodide perovskite (CH3NH3PbI3) is discussed. Issues include the low activation barrier of vacancy migration and the high diffusivities of iodine vacancies and interstitials. Comparisons are also made with the behaviour of point defects in the oxide perovskite SrTiO3. [ABSTRACT FROM AUTHOR]

We report the synthesis and crystal structure of an organic–inorganic compound, ethylenediammonium lead iodide, NH3CH2CH2NH3PbI4. Synchrotron-based single crystal X-ray diffraction experiments revealed that the pristine and thermally treated crystals differ in the organic cation behaviour, which is characterized by a partial disorder in the thermally treated crystal. Based on current–voltage measurements, increased disorder of the organic cation is associated with enhanced photoconductivity. This compound could be a potential candidate for interface engineering in lead halide perovskite-based optoelectronic devices. [ABSTRACT FROM AUTHOR]

We report the synthesis and crystal structure of an organic–inorganic compound, ethylenediammonium lead iodide, NH3CH2CH2NH3PbI4. Synchrotron-based single crystal X-ray diffraction experiments revealed that the pristine and thermally treated crystals differ in the organic cation behaviour, which is characterized by a partial disorder in the thermally treated crystal. Based on current–voltage measurements, increased disorder of the organic cation is associated with enhanced photoconductivity. This compound could be a potential candidate for interface engineering in lead halide perovskite-based optoelectronic devices. [ABSTRACT FROM AUTHOR]

Haloplumbate-based perovskites display promising functionalities for advanced photovoltaic, optoelectronic and other applications with high performances and low costs. Herein, we present a study of variable-temperature crystal structures, dielectrics and conductance at 153–513 K, and luminescence at ambient temperature for a one-dimensional organic–inorganic perovskite, [N-methyldabconium]PbI3 (1). Hybrid 1 shows extra thermo- and water-stability (thermal decomposition at ca. 653 K), switchable dielectric behaviour and conductance at around 348 K, owing to symmetry-breaking structure phase transition from the hexagonal space group P63/mmc in the high-temperature phase to the orthogonal space group Pcba in the low-temperature phase, and bright yellow-green emission at room temperature, originating from the electron transition within the semiconducting {PbI3}∞ chains. This study will broaden the scope of lead halide-based hybrid materials for practical application in optical and electrical devices. [ABSTRACT FROM AUTHOR]

We investigate the variable temperature (100–450 K) and high-pressure (p = ambient − 0.74 GPa) crystal chemistry of the black perovskite formamidinium lead iodide, [(NH2)2CH]PbI3, using single crystal X-ray diffraction. In both cases we find a phase transition to a tetragonal phase. Our experimental results are combined with first principles calculations, providing information about the electronic properties of [(NH2)2CH]PbI3 as well as the most probable orientation of the [(NH2)2CH]+ cations. [ABSTRACT FROM AUTHOR]

The crystal structure of a new perovskite material, (C4H8NH2)PbI3 was determined and illustrated by single crystal X-ray diffraction. UV spectra, photoluminescence and XRD results show it is a promising alternative to hybrid organic–inorganic perovskites due to it's good water resistance and suitable bandgap. [ABSTRACT FROM AUTHOR]

We present a new transformation route from PbS to CH3NH3PbI3 for the facile preparation of perovskites with all kinds of shapes via vapor-assisted chemical bath deposition (VACBD). As such, curved and large-area CH3NH3PbI3 films with high quality are successfully achieved, which are suitable for the manufacturing scale-up of perovskite solar cells. [ABSTRACT FROM AUTHOR]

To obtain bulk cubic CH3NH3PbI3, chlorobenzene was employed to regulate the CH3NH3PbI3γ-butyrolactone solution with high saturated solubility at room temperature and a high yield of crystal at 60 °C. As a result, bulk cubic CH3NH3PbI3 single crystal was successfully synthesized for the first time in mixed-solvent method at 60 °C, which is a little higher than the tetragonal–cubic phase inversion temperature. [ABSTRACT FROM AUTHOR]

Perovskite films were prepared using single step solution deposition at different annealing temperatures and annealing times. The crystal structure, phases and grain size were investigated with XRD, XPS and SEM/EDX. The prepared films show a typical orientation of tetragonal perovskite phase and a gradual transition at room temperature from the yellow intermediate phase to the black perovskite phase. Films with high purity were obtained by sintering at 100 °C. In addition, the chemical composition and crystal struture of intermediate phase were investigated in detail. FTIR, UV-vis and NMR spectra revealed the occurance of DMF complexes. Interestingly, the intermediate phase could be transformed to the black perovskite phase upon X-ray irradiation. In addition, the recovery of the aged perovskite films from a yellow intermediate phase back to the black perovskite was shown to be viable via heating and X-ray irradiation. [ABSTRACT FROM AUTHOR]

High-quality formamidinium lead iodide (FAPbI3) perovskite thin films are fabricated via organic cation exchange. With ammonia lead iodide (NH4PbI3) as the starting material, the NH4+ in NH4PbI3 could be gradually substituted by FA+ in formamidine acetate (FA-Ac) and simultaneously transformed to the pure phase α-FAPbI3 at elevated temperature. [ABSTRACT FROM AUTHOR]

Organic and inorganic hybrid perovskites (e.g., CH3NH3PbI3), with advantages of facile processing, tunable bandgaps, and superior charge-transfer properties, have emerged as a new class of revolutionary optoelectronic semiconductors promising for various applications. Perovskite solar cells constructed with a variety of configurations have demonstrated unprecedented progress in efficiency, reaching about 20% from multiple groups after only several years of active research. A key to this success is the development of various solution-synthesis and film-deposition techniques for controlling the morphology and composition of hybrid perovskites. The rapid progress in material synthesis and device fabrication has also promoted the development of other optoelectronic applications including light-emitting diodes, photodetectors, and transistors. Both experimental and theoretical investigations on organic–inorganic hybrid perovskites have enabled some critical fundamental understandings of this material system. Recent studies have also demonstrated progress in addressing the potential stability issue, which has been identified as a main challenge for future research on halide perovskites. Here, we review recent progress on hybrid perovskites including basic chemical and crystal structures, chemical synthesis of bulk/nanocrystals and thin films with their chemical and physical properties, device configurations, operation principles for various optoelectronic applications (with a focus on solar cells), and photophysics of charge-carrier dynamics. We also discuss the importance of further understanding of the fundamental properties of hybrid perovskites, especially those related to chemical and structural stabilities. [ABSTRACT FROM AUTHOR]

Photo-excitation intensity dependent electron and hole injections from CH3NH3PbI3 perovskite to nanocrystalline TiO2 and spiro-OMeTAD are presented with the electron injection yield decrease from 95% to 10% and the hole injection yield decrease from 99% to 50% by increasing the excitation intensity from 10 nJ cm−2 to 50 μJ cm−2. [ABSTRACT FROM AUTHOR]

Uniform CH3NH3PbI3 perovskite thin films with high phase purity and micron-sized pinhole-free grains have been successfully synthesised on fluorine-doped tin oxide (FTO) glass substrates using a novel two-step sequential aerosol-assisted chemical vapour deposition (AACVD) process. [ABSTRACT FROM AUTHOR]

Recently, highly efficient solar cells based on organic–inorganic perovskites have been intensively studied for developing fabricating methods and device structures. To improve the performance of perovskite film devices, delicate control of charge transfer material interconnectivity is required. Here, controlling the mesoporous TiO2 structure improves their charge collection and injection rate, and allows substantial enhancement of the corresponding device performance. We found that increasing the TiCl4 processing time deteriorates the device performance by introducing a large amount of excessively large perovskite particles, surface roughness and charge recombination. Proper TiCl4 processing dramatically improves the charge transport within the electron transfer layer, explaining the efficient performance of meso-superstructured solar cells. [ABSTRACT FROM AUTHOR]

In the present Communication we discuss a field-induced and photoinduced self-doping chemistry resulting in the formation of the positively and negatively charged vacancies in the MAPbI3 perovskite films. These vacancies induce p-type and n-type doping of the perovskite absorber leading to the realization of the p-i-n device operation mechanism. [ABSTRACT FROM AUTHOR]

A novel, aqueous precursor system (Pb(NO3)2 + water) is developed to replace conventional (PbI2 + DMF) for fabricating methylammonium lead iodide (MAPbI3) perovskite solar cells (PSCs). When the morphology and surface coverage of the Pb(NO3)2 film was controlled during coating, a power conversion efficiency of 12.58% under standard conditions (AM1.5, 100 mW cm−2) was achieved for the PSC. [ABSTRACT FROM AUTHOR]

Photocurrent measurements on devices containing perovskite (CH3NH3)PbI3 show two distinct spectral responses when deposited in a mesoporous oxide matrix, compared with one response for planar perovskite alone. With a TiO2 matrix, the shorter wavelength response has an inverted temperature response with increasing performance on cooling. [ABSTRACT FROM AUTHOR]

The methylammonium cation in [CH3NH3]PbI3 demonstrates increasing positional disorder on heating from 100 K to 352 K. In the tetragonal phase, stable between 165 K and 327 K, the cation is disordered over four sites directed toward the faces of the distorted cubic [PbI3]− framework and migrates towards the cavity centre with increasing temperature. [ABSTRACT FROM AUTHOR]

We report the synthesis and characterisation of tetra{4-[N,N-(4,4′-dimethoxydiphenylamino)]phenyl}ethene (TAE-1) as an efficient and robust hole transport material for its application in methyl ammonium lead iodide (MAPI) perovskite solar cells. The solar cells show light-to-energy conversion efficiencies as high as 11.0% under standard measurement conditions without the need of additional dopants. [ABSTRACT FROM AUTHOR]

A simple vacuum deposition method for the preparation of high quality hybrid organic–inorganic methylammonium lead iodide perovskite thin films is reported. When sandwiched in between organic charge transporting layers, such films lead to solar cells with a power conversion efficiency of 12.2%. [ABSTRACT FROM AUTHOR]