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Organometallic lead halide perovskite powders have gained widespread attention for their intriguing properties, showcasing remarkable performance in the optoelectronic applications. In this study, formamidinium lead iodide (α‐FAPbI3) microcrystals (MCs) is synthesized using retrograde solubility‐driven crystallization. Additionally, methylammonium lead bromide (MAPbBr3) and cesium lead iodide (δ‐CsPbI3) MCs are prepared through a sonochemical process, employing low‐grade PbX2 (X = I & Br) precursors and an eco‐friendly green solvent (γ‐Valerolactone). The study encompasses an analysis of the structural, optical, thermal, elemental, and morphological characteristics of FAPbI3, MAPbBr3, and CsPbI3 MCs. Upon analysing phase stability, a phase transition in FAPbI3 MCs is observed after 2 weeks. To address this issue, a powder‐based mechanochemical method is employed to synthesize stable mixed cation perovskite powders (MCPs) by subjecting FAPbI3 and MAPbBr3 MCs with varying concentrations of CsPbI3. Furthermore, the performance of mixed cation perovskites are examined using the Solar Cell Capacitance Simulator (SCAPS‐1D) software. The impact of cesium incorporation in the photovoltaic characteristics is elucidated. All mixed cation absorbers exhibited optimal device performance with a thickness ranging between 0.6–1.5 µm. It's worth noting that the MCPs exhibit impressive ambient stability, remaining structurally intact and retaining their properties without significant degradation for 70 days of ambient exposure. [ABSTRACT FROM AUTHOR]

Hybrid lead iodide perovskites are promising photovoltaic and light-emitting materials. Extant literature data on the key optoelectronic and luminescent properties of hybrid perovskites indicate that these properties are affected by electron–phonon coupling, the dynamics of the organic cations, and the degree of lattice distortion. We report temperature-dependent Raman studies of BA2MAPb2I7 and BA2MA2Pb3I10 (BA = butylammonium; MA = methylammonium), which undergo two structural phase transitions. Raman data obtained in broad temperature (360–80 K) and wavenumber (1800–10 cm−1) ranges show that ordering of BA+ cations triggers the higher temperature phase transition, whereas freezing of MA+ dynamics occurs below 200 K, leading to the onset of the low-temperature phase transition. This ordering is associated with significant deformation of the inorganic sublattice, as evidenced by changes observed in the lattice mode region. Our results show, therefore, that Raman spectroscopy is a very valuable tool for monitoring the separate dynamics of different organic cations in perovskites, comprising "perovskitizer" and interlayer cations. [ABSTRACT FROM AUTHOR]

Homochiral halide perovskites have gained increasing attention because of their fascinating optoelectronic properties and prospective applications in laser technologies. However, the limited choice of chiral organic templates severely restricts their structural diversity and second‐harmonic generation (SHG) effects. Here, we present an in situ chiral template approach for the synthesis of one‐dimensional (1D) homochiral lead iodides. A chiral imine (L‐ipp) template was generated in situ by reacting L‐proline (L‐pro) and acetone under ambient conditions. Notably, L‐ipp can cooperate with L‐pro to direct the formation of a homochiral lead iodide with dual chiral templates, which is unprecedented in crystalline metal halides. The homochiral lead iodide containing both L‐ipp and L‐pro shows a strong SHG response of 8.0 times that of KH2PO4 (8.0×KDP). The SHG efficiency is one of the largest values reported to date for any homochiral lead halides under 1064 nm laser irradiation. A comparative study shows that homochiral 1D lead iodides containing either L‐ipp or L‐pro exhibit relatively weak SHG responses (≤1.0×KDP). This work demonstrates the advantage of using two different chiral templates over a single chiral template in enhancing the SHG responses of halide materials. [ABSTRACT FROM AUTHOR]

The presence of residual lead iodide phase in perovskite films, inherent to the two‐step spin‐coating method, has been reported to be beneficial for the performance of perovskite solar cells (PSCs); However, it may potentially undermine the photostability of PSCs. Herein, four distinct sets of perovskite films and devices are fabricated via the two‐step spin‐coating process, each under different processing conditions. All conditions demonstrate promising power conversion efficiency in PSCs. However, the aspect of photostability is found to be significantly influenced by unreacted PbI2 in the perovskite films. Varying degrees of residual PbI2 are detected among these films. Upon light exposure, it is observed that residual PbI2 within perovskites undergoes decomposition into metallic lead (Pb0) and mobile iodine, and these can affect the photovoltaic performance of the PSCs. The presence of mobile ions in metal–halide perovskites has generated substantial concern due to their impact on hysteresis within the J–V curve. Furthermore, the metallic lead (Pb0) containing perovskite films exhibits a prominent inverted hysteresis in the J–V curve [ABSTRACT FROM AUTHOR]

The photovoltaic, luminescence, and detector fields have witnessed the robust application prospects of solution‐processed halide perovskites. Deep insights into solution can pave the way toward the precise crystallization control of halide perovskites for giving full play to the advantages of those materials. Herein, the dissolution behavior of formamidinium lead iodide (FAPbI3) together with lead iodide in amide solvents with regulated coordination ability at increasing temperature and under different molar ratio between formamidinium iodide (FAI) and PbI2 is studied. The solvent coordination ability, temperature, and FAI/PbI2 molar ratio demonstrate equivalent influence on the dissolution, and increasing those factors tends to increase the solubility first and decrease it then for Pb compounds. It is proposed that there are interchangeable Pb solute forms including solvent‐containing lead complexes and solvated lead halide fragments in solution and the interconversion of both solutes driven by the above factors brings the solubility change. The modulated dissolution affects the crystallization behaviors of FAPbI3 when preparing single crystals, nanocrystal dispersions, and thin films, and allows for regulated crystallinity in printable mesoscopic solar cells which demonstrate a power conversion efficiency of 18.40%. [ABSTRACT FROM AUTHOR]

Inorganic halide perovskites, such as CsPbI3, have unique optoelectronic properties which made them promising candidates for several applications. Unfortunately, these perovskites undergo rapid chemical decomposition and transformation into yellow δ-phase. Thus, the synthesis of stable cesium lead iodide perovskites remains an actual challenging field and it is imperative to develop a stabilized black phase for photovoltaic applications. For this purpose, a surfactant ligand was used to control the synthesis of inorganic perovskite CsPbI3 nanoparticles. Herein we demonstrate a new avenue for lead halide perovskites with the addition of either hexadecyltrimethylammonium bromide (CTAB) or silica nanoparticles to maintain in the first place; the stability of the α-CsPbI3 phase, and later on to boost their photoluminescence quantum yield (PLQY). The prepared perovskites were characterized using UV–visible absorption spectroscopy, fluorescence spectroscopy, scanning electron microscopy, thermogravimetric analysis and X-Ray diffraction technique. Results show higher stability of α-CsPbI3 phase and improvement in PLQY % to reach 99% enhancement in presence of CTAB. Moreover, the photoluminescence intensity of CsPbI3 nanoparticles was higher and was maintained for a longer duration in the presence of CTAB. [ABSTRACT FROM AUTHOR]

Wide‐bandgap (WBG) perovskite solar cells (PSCs) have garnered significant attention for their potential applications in tandem solar cells. However, their large open‐circuit voltage (VOC) deficit and serious photo‐induced halide segregation remain the main challenges that impede their applications. Herein, a post‐treatment strategy without thermal annealing is presented to form a 2D top layer of 2‐thiopheneethylammonium lead halide (n = 1) on WBG perovskites. This thermal annealing‐free post‐treatment method can more effectively passivate the defects of WBG methylamine (MA)‐free formamidinium/cesium lead iodide/bromide perovskite films and suppress photo‐induced perovskite phase segregation, as compared with the thermal annealing method that yields multi‐2D phases. The resulting opaque and semi‐transparent 1.66 eV‐bandgap perovskite solar cells deliver maximum power conversion efficiencies of 21.47% (a small VOC deficit of 0.43 V) and 19.11%, respectively, both of which are among the highest reports for inverted MA‐free WBG PSCs. Consequently, four‐terminal all‐perovskite tandem cells realize a remarkable efficiency of 26.64%, showing great promise for their applications in efficient multi‐junction tandem solar cells. [ABSTRACT FROM AUTHOR]

Fast reaction between organic salt and lead iodide always leads to small perovskite crystallites and concentrated defects. Here, polyacrylic acid is blended with organic salt, so as to regulate the crystallization in a two‐step growth method. It is observed that addition of polyacrylic acid retards aggregation and crystallization behavior of the organic salt, and slows down the reaction rate between organic salt and PbI2, by which "slow‐release effect" is defined. Such effect improves crystallization of perovskite. X‐ray diffraction study shows that, after addition of 2 mm polyacrylic acid, average crystallite size of perovskite increases from ≈40 to ≈90 nm, meanwhile, grain size increases. Thermal admittance spectroscopy study shows that trap density is reduced by nearly one order (especially for deep energy levels). Due to the improved crystallization and reduced trap density, charge recombination is obviously reduced, while lifetime of charge carriers in perovskite film and devices are prolonged, according to time‐resolved photoluminescence and transient photo‐voltage decay curve tests, respectively. Accordingly, power conversion efficiency of the device is promoted from 19.96 (±0.41)% to 21.84 (±0.25)% (with a champion efficiency of 22.31%), and further elevated to 24.19% after surface modification by octylammonium iodide. [ABSTRACT FROM AUTHOR]

Herein, we reported the fabrication of methyl ammonium lead iodide (MAPbI 3) based perovskite solar cells (PSCs). Molybdenum diselenide (MoSe 2) was hydrothermally prepared and used as an additive to control the rapid crystallization of MAPbI 3. Different weight percentage of (0.1, 0.2, 0.3, 0.4, 0.5 and 0.7 %) of the MoSe 2 additive was explored to control the crystallization process and improve the surface morphological characteristics of the MAPbI 3. The obtained results showed that 0.5 % MoSe 2 additive modified MAPbI 3 based PSCs device demonstrated excellent efficiency of 15.1 % with open circuit voltage (Voc) = 0.99 V, photocurrent-density (Jsc) = 21.26 mA/cm2 and fill factor (FF) = 0.72. The fabricated device with 0.5 % MoSe 2 additive retained more than 85 % efficiency whereas pristine MAPbI 3 based device retained 49.56 % efficiency after 1200 h. This suggested that 0.5 % MoSe 2 additive modified MAPbI 3 based PSCs device has excellent stability compared to the pristine MAPbI 3 based PSCs device. • MoSe 2 has been used as additive to improve MAPbI 3 morphology. • MoSe 2 + MAPbI 3 based perovskite solar cells exhibited good PCE. • The fabricated device exhibited good stability. [ABSTRACT FROM AUTHOR]

The delicate control of the crystallization behavior of the perovskite layer is critical for achieving high power conversion efficiency (PCE) and longer-term stability of perovskite solar cells (PSCs). Residual lead iodide (PbI2) was usually evitable in the two-step processed perovskite film due to incomplete reaction; however, its exact effects on the perovskite layer and resulting PSCs were not well elucidated so far. Here, the lead halide perovskite films were grown by the two-step process, where the residual PbI2 can be fine controlled by the concentration of organic salt solution. Results indicated that the properties of the perovskite layer may be varied greatly depending on the amount of residual PbI2, and a series of beneficial effects for PSCs can be achieved via suitable management of residue PbI2, i.e., prolonged carrier diffusion capacity, reduced defect density, inhibited ion migration, and interfacial charge recombination. Accordingly, an impressive PCE of 22.4% was achieved from the PSCs with optimized PbI2. Furthermore, the PSCs also displayed fairly good operational stability and retained 68% of its initial PCE after 400 h (at continuous irradiation under 1-sun illumination). This work may inspire solutions for further enhancing the performance of PSCs via fine controlled residual PbI2 in the perovskite layer. [ABSTRACT FROM AUTHOR]

Light‐harvesting devices made from lead sulfide quantum dot (QD) absorbers are one of the many promising technologies of third‐generation photovoltaics. Their simple, solution‐based fabrication, together with a highly tunable and broad light absorption makes their application in newly developed solar cells, particularly promising. In order to yield devices with reduced voltage and current losses, PbS QDs need to have strategically passivated surfaces, most commonly achieved through lead iodide and bromide passivation. The interdot spacing is then predominantly filled with residual amorphous lead halide species that remain from the ligand exchange, thus hindering efficient charge transport and reducing device stability. Herein, it is demonstrated that a post‐treatment by iodide‐based 2‐phenylethlyammonium salts and intermediate 2D perovskite formation can be used to manage the lead halide excess in the PbS QD active layer. This treatment results in improved device performance and increased shelf‐life stability, demonstrating the importance of interdot spacing management in PbS QD photovoltaics. [ABSTRACT FROM AUTHOR]

In recent years the development of autonomous photo‐rechargeable batteries has received growing attention. Especially highly integrated photobatteries based on multifunctional materials able to harvest sunlight and store charge carriers are the holy grail amongst such devices. Recently 2‐(1‐cyclohexenyl)ethyl ammonium lead iodide (CHPI) has been reported as multifunctional photoelectrode material for the design of highly integrated Li‐ion photobatteries. CHPI is thereby believed to be able to reversibly intercalate Li‐ions from polar carbonate‐based electrolytes, typically used in Li‐ion batteries (LIBs). Herein, CHPI is examined closer to investigate its stability against dissolution, the possibility of Li‐intercalation and photo‐assisted deintercalation, and its general behavior under illumination in standard carbonate‐based electrolytes as well as in a newly developed low polarity electrolyte based on ortho‐difluorobenzene (o‐DFB). This study demonstrates that CHPI dissolves in contact with carbonate‐based electrolytes while being stable in o‐DFB‐based electrolyte and that no Li‐intercalation takes place in the latter. Furthermore, CHPI irreversibly photo‐corrodes during illumination and photo‐assisted deintercalation of lithium ions is not detected. These results lead to the conclusion, that CHPI is neither a suitable nor a stable material for the design of Li‐ion‐based photo‐rechargeable batteries and similar behavior for other organic–inorganic lead halide perovskite materials is expected. [ABSTRACT FROM AUTHOR]

A variety of different synthesis methods for the fabrication of solar cell absorbers based on the lead halide perovskite methylammonium lead iodide (MAPbI3, MAPI) have been successfully developed in the past. In this work, we elaborate upon vacuum-based dual source co-evaporation as an industrially attractive processing technology. We present non-stationary processing schemes and concentrate on details of co-evaporation schemes where we intentionally delay the start/end points of one of the two evaporated components (MAI and PbI2). Previously, it was found for solar cells based on a regular n-i-p structure, that the pre-evaporation of PbI 2 is highly beneficial for absorber growth and solar cell performance. Here, we apply similar non-stationary processing schemes with pre/post-deposition sequences for the growth of MAPI absorbers in an inverted p-i-n solar cell architecture. Solar cell parameters as well as details of the absorber growth are compared for a set of different evaporation schemes. Contrary to our preliminary assumptions, we find the pre-evaporation of PbI2 to be detrimental in the inverted configuration, indicating that the beneficial effect of the seed layers originates from interface properties related to improved charge carrier transport and extraction across this interface rather than being related to an improved absorber growth. This is further evidenced by a performance improvement of inverted solar cell devices with pre-evaporated MAI and post-deposited PbI2 layers. Finally, we provide two hypothetical electronic models that might cause the observed effects. [ABSTRACT FROM AUTHOR]

Lead halide perovskite materials are promising candidates for the application of semitransparent solar cells due to their bandgap tunability and high device efficiencies. The high absorption coefficient of these materials, however, makes it difficult to attain high average visible transmittance values without compromising the power conversion efficiencies (PCEs). In this work, a co‐evaporation process is employed to fabricate thin (50 and 100 nm) methylammonium lead iodide (MAPI) perovskite films and integrate them in semitransparent perovskite solar cells (ST‐PSCs). Due to the compact nature of the thin MAPI films, the resultant fully vacuum and room temperature‐processed devices demonstrate high fill factor values approaching 80% and open‐circuit voltage values close to 1100 mV. As a result of this, the ST‐PSCs exhibit PCE's as high as 9% with a photopic average visible transmittance of the full device of 23%. [ABSTRACT FROM AUTHOR]

The remarkable performance of organometallic lead halide perovskites in solar cell technology has drawn attention due to their intriguing properties. Commercialization of perovskite solar cell (PSC) technology is hampered by high-cost device fabrication techniques and inadequate stability under ambient conditions. In this study, we used low-grade PbI2 to make highly stable Methylammonium lead Iodide (MAPbI3) powder via sono-chemical method, in order to reduce the cost of the PSCs. The sono-chemical method is used to synthesize MAPbI3 microcrystals because of its significant advantages, including morphological control and educt dissolution support. The tetragonal phase of the synthesized perovskite (MAPbI3) powder was confirmed using PXRD measurement. The synthesized MAPbI3 powder was then subjected to series of analysis, including UV–Vis–NIR absorption, PL Emission, FTIR and TGA. The FESEM and TEM analyses reveal that the size of synthesized MAPbI3 microcrystals is in the range of 0.3–2 μm. The optical and photovoltaic properties of conventional solution-based films and powder-based recrystallization films were studied and compared their performance in the carbon-based perovskite solar cell (C-PSC). The powder-based solar cell exhibits slightly higher power conversion efficiency (10.1%) than the device fabricated by conventional solution-based approach (9.5% for high-grade PbI2 + MAI and 6.8% for low-grade PbI2 + MAI). The enhanced photovoltaic characteristics of the recrystallization-based devices were attributed to the homogeneous perovskite film with large grain size and high crystalline properties. [ABSTRACT FROM AUTHOR]

Lead halide 2D hybrid perovskites (HP) have emerged as promising materials for photovoltaic and lighting applications. Solvent‐free preparations offer greener route, but require congruent melting of halide perovskite for thin films, which has been demonstrated only for monolayered HP (n=1 of the (A)2(MA)n−1PbnI3n+1 series) at the quite high temperature Tm (Tmelting) of 171 °C. Here, we report on the solvent‐free preparation (n=2, 4), thermal behaviour and melt‐processed thin films of a series of HP (GABA)2(MA)n−1PbnI3n+1 (n=1, 2, 4; GABA+: 4‐ammoniumbutyric acid cation). The n=1 and n=2 HP have an exceptional low congruent Tm of 126 °C and 136 °C, respectively, and, for n=1, a very good stability in the molten state. The liquid–solid reaction of molten (GABA)2PbI4 or (GABA)2(MA)Pb2I7 with MAPbI3 in 1/1 (T=130 °C) or 1/2 (T=135 °C) ratio leads to pure phases of the n=2 HP and (GABA)2(MA)3Pb4I11 (n=4, Tm=185 °C), respectively. Melt‐processed thin films of n=1, n=2 and n=4 HP have also been prepared. [ABSTRACT FROM AUTHOR]

Lead halide perovskites are semiconductor materials which are employed as nonintentionally doped absorbers inserted between two selective carrier transport layers (SCTL), realizing a p‐i‐n or n‐i‐p heterojunction. In our study, we have developed and investigated a lateral device, based on methylammonium lead iodide (MAPbI3) in which the p‐i‐n heterojunction develops in the horizontal direction. Our research suggests that the effective doping level in the MAPbI3 film should be very low, below 1012 cm−3. Along the vertical direction, this doping level is not enough to screen the electric field of the buried heterojunction with the SCTL. The perovskite work function is therefore affected by the work function of the SCTL underneath. From drift‐diffusion simulations, we show that intrinsic perovskite‐SCTL structures develop mV range surface photovoltages (SPVs) under continuous illumination. However, perovskite‐SCTL structures can develop SPVs of hundreds of mV, as confirmed by our measurements. We therefore analyzed the compatibility between low doping and low defect densities in the perovskite layer and such high SPV values using numerical modeling. It is shown that these high SPV values could originate from electronic processes due to large band offsets in the buried perovskite‐SCTL heterojunctions, or at the SCTL‐transparent conductive oxide (TCO) buried heterojunction. However, such electronic processes can hardly explain the long SPV persistence after switching off the illumination. [ABSTRACT FROM AUTHOR]

Scalable thin‐film deposition methods are increasingly important for hybrid lead halide perovskite thin films. Understanding the structure evolution during non‐equilibrium processes helps to find suitable materials and processing parameters to produce films with well‐performing optoelectronic properties. Here, spin‐cast and slot‐die coated bilayers of lead iodide (PbI2) and methylammonium iodide (MAI) are investigated by in situ grazing‐incidence wide‐angle X‐ray scattering during the thermal annealing process, which converts the bilayer into methylammonium lead iodide (MAPI). Photoluminescence (PL) and UV/Vis measurements show increasing crystallinity during the annealing process and a slight PL red‐shift of the spin‐cast film, attributed to crystallite coalescence that is not prominent for the slot‐die coated film. The disintegration of the solvent‐precursor complex (MA)2(Pb3I8) ⋅ 2 DMSO and conversion into perovskite are followed in situ and differences in the morphology and time evolution are observed. In both, spin‐cast and slot‐die coated thin‐films, the isotropic orientation is dominant, however, in the slot‐die coated films, the perovskite crystallites have an additional face‐on orientation ((110) parallel to substrate) that is not detected in spin‐cast films. An Avrami model is applied for the perovskite crystal growth that indicates reduced dimensionality of the growth for the printed thin films. [ABSTRACT FROM AUTHOR]

Summary: Organic‐inorganic lead halide perovskite solar cells (PSCs) have shown excellent characteristics for photovoltaic performance along with high power conversion efficiency (PCE) of 25.5%. Methylammonium lead iodide (CH3NH3PbI3) PSCs show effective photovoltaic performance but exhibit low utilization and instability in the ultraviolet (UV) region due to photodegradation. Therefore, there is a need for research aimed at increasing the stability of PSCs. Through their down‐conversion, PSCs can achieve high photovoltaic performance and stability by protecting against UV light and light‐harvesting in the visible region. In this study, europium (Eu; a lanthanide) was demonstrated to enhance the efficiency of PSCs and prevent degradation by UV light. The Eu‐complex poly(dimethylsiloxane) (PDMS) film enhanced the usability of the UV region by down‐converting UV light to visible light. In addition, Eu‐complex PDMS film has the advantages of being transparent and hydrophobic. Furthermore, it is easily detachable when the surface is contaminated. When Eu‐complex PDMS film was attached and compared with a reference device, it was confirmed that the PCE increased by up to 20% and that the short‐circuit current density also increased. Overall, Eu‐complex film was shown to increase the light‐harvesting of PSCs and enhance the stability in the UV region through the down‐conversion of UV light to visible light. [ABSTRACT FROM AUTHOR]

The unprecedented structural flexibility of hybrid halide perovskites is accompanied by a wide range of useful optoelectronic properties, causing a high interest in this family of materials. However, there are no systematic studies yet on the relationships between the topology of structures derived of chain 1D hybrid halide perovskites and their optoelectronic properties such as the band gap as already reported for 3D and 2D hybrid halide perovskites. In the present work, we introduce a rational classification of hybrid lead iodide 1D structures. We provide a theoretical assessment of the relationship between the topology of 1D hybrid halide perovskite-derived structures with vertex-connected octahedra and show that the distortions of geometry of the chains of PbI6 octahedra are the main parameters affecting the band gap value while the distance between the chains of vertex-connected octahedra has a minor effect on the band gap. [ABSTRACT FROM AUTHOR]

Organic ammonium salts (OASs) have been widely used to passivate perovskite defects. The passivation mechanism is usually attributed to coordination of OASs with unpaired lead or halide ions, yet ignoring their interaction with excess PbI2 on the perovskite film. Herein, we demonstrate that OASs not only passivate defects by themselves, but also redistribute excess aggregated PbI2 into a discontinuous layer, augmenting its passivation effect. Moreover, alkyl OAS is more powerful to disperse PbI2 than a F‐containing one, leading to better passivation and device efficiency because F atoms restrict the intercalation of OAS into PbI2 layers. Inspired by this mechanism, exfoliated PbI2 nanosheets are adopted to provide better dispersity of PbI2, further boosting the efficiency to 23.14 %. Our finding offers a distinctive understanding of the role of OASs in reducing perovskite defects, and a route to choosing an OAS passivator by considering substitution effects rather than by trial and error. [ABSTRACT FROM AUTHOR]

We investigated the structural properties of organic–inorganic lead halide perovskite microwires through joint experimental and theoretical Raman spectroscopy. High‐quality methyl ammonium lead iodide (MAPBI3, MA = CH3NH3+) microwires with tetragonal phases and explicit crystalline orientation were prepared. Raman spectroscopy was used in studying the as‐prepared microwires and determining not only the crystal quality but also crystalline orientation of MAPBI3 with the aid of normal mode calculations. High‐quality structural features were verified by well‐resolved Raman peaks related to the inorganic cage (IPbI stretching and bending modes below 100 cm−1), organic MA cation motions (libration ~150–200 cm−1 and torsional ~200–250 cm−1), a coupled mode of cage and MA cation liberation (~105–110 cm−1), and the almost undetectable degraded signal at 95 cm−1. In micro‐Raman mapping, an intensity ratio of 105 and 95 cm−1 was used for the direct imaging of crystal quality along the microwire. The characterization of the crystalline orientation of MAPBI3 microwires posed a challenge, which can be addressed by using polarized Raman technique with normal mode analysis. We believe that the proposed method can be extended to other organic–inorganic lead halide perovskites with different structures, such as polycrystalline films and single crystals. [ABSTRACT FROM AUTHOR]

2H-type lead iodide (PbI2) is a two-dimensional (2D) layered semiconductor and has recently received considerable attention as a precursor for lead halide perovskite solar cells. Although the pressure-induced structural phase transitions of PbI2 have been investigated for several decades, the detailed crystalline structure of PbI2 at high pressure is still elusive because of lacking in situ x-ray diffraction (XRD) studies. In this report, in situ Raman spectra and XRD patterns of 2H-PbI2 under pressure have been investigated in a diamond-anvil cell. Both Raman spectra and XRD patterns provide consistent evidence for two structural phase transitions upon compression at approximately 0.58 and 2.6 GPa. The XRD patterns suggest that the complete pressure-driven phase transition sequence of PbI2 up to 20 GPa is two-dimensional hexagonal 2H- P 3 ¯ m 1 →polytype 4H-P3m1→three-dimensional (3D) orthorhombic Pnma. The uncovered 2D to 3D structural transition in 2H-PbI2 advances the understanding of structural stability of 2H-type layered semiconductors and lead halide perovskite. [ABSTRACT FROM AUTHOR]

2H-type lead iodide (PbI2) is a two-dimensional (2D) layered semiconductor and has recently received considerable attention as a precursor for lead halide perovskite solar cells. Although the pressure-induced structural phase transitions of PbI2 have been investigated for several decades, the detailed crystalline structure of PbI2 at high pressure is still elusive because of lacking in situ x-ray diffraction (XRD) studies. In this report, in situ Raman spectra and XRD patterns of 2H-PbI2 under pressure have been investigated in a diamond-anvil cell. Both Raman spectra and XRD patterns provide consistent evidence for two structural phase transitions upon compression at approximately 0.58 and 2.6 GPa. The XRD patterns suggest that the complete pressure-driven phase transition sequence of PbI2 up to 20 GPa is two-dimensional hexagonal 2H- P 3 ¯ m 1 →polytype 4H-P3m1→three-dimensional (3D) orthorhombic Pnma. The uncovered 2D to 3D structural transition in 2H-PbI2 advances the understanding of structural stability of 2H-type layered semiconductors and lead halide perovskite. [ABSTRACT FROM AUTHOR]

Long‐term stability has become the major obstacle for the successful large‐scale application of perovskites devices. Owing to the ionic nature of metal‐halide perovskites, the interfacial ion diffusion can induce irreversible degradation under operational conditions, which presents a great challenge to realize stable perovskite solar modules. Here, a diphenylphosphine oxide compound, ethane‐1,2‐diylbis(diphenylphosphine oxide) (DPPO) is introduced to coordinate with lead iodide and form a cross‐linked 1D Pb3I6‐DPPO (1D‐PbI2) complex. These judiciously designed cross‐linked nonionic low‐dimensional lead halide/organic adducts can passivate the defects of perovskite while acting as a robust ion diffusion barrier, thus significantly improving the electronic quality and intrinsic stability of perovskite films. As a result, high‐performance inverted (p‐i‐n) solar modules with a champion efficiency approaching 19% (a certified stabilized efficiency of 17.8%) for active device areas above 17 cm2 without the use of antisolvents, accompanied by outstanding operational stability under heat stress and continuous illumination are achieved. [ABSTRACT FROM AUTHOR]

Lattice dynamics are often regarded as signatures of the underlying crystal structure. Here, a first‐principle‐based effective Hamiltonian method combined with molecular dynamics simulations is used to study dynamical behaviors of CsPbI3 perovskite across temperature and structural phase transitions. A single (short‐range tilting) parameter in this effective Hamiltonian is varied in order to make the temperature range of the intermediate tetragonal P4/mbm phase, existing in‐between the cubic Pm3¯m and orthorhombic Pnma phases, either broader than observed or completely disappearing. Comparing the dynamics of these different cases allows one to conclude that real CsPbI3 perovskite should have i) two iodine‐octahedral‐tilt related modes that differ in frequency but both significantly soften as the temperature decreases within the cubic phase toward the Pm3¯m‐to‐P4/mbm transition; and ii) one mode that maintains a very low frequency (of the order of 1.0 cm−1) in the entire region of P4/mbm stability, as a result of the temporal exploration of various structural states. Such latter sub‐THz mode mixes fluctuations of antiphase iodine tiltings and Cs antipolar motions because of a trilinear energetic coupling. [ABSTRACT FROM AUTHOR]

Halide perovskite materials have attracted great interest for applications in low-cost, solution-processed solar cells and other optoelectronics applications. The role of moisture in perovskite device degradation and crystal formation processes remains poorly understood. Here, we use a data-driven approach to discover the influence of trace amounts of water on perovskite crystal formation by analyzing a comprehensive dataset of 8470 inverse-temperature crystallization lead iodide perovskite synthesis reactions, performed over 20 months using a robotic system. We identified discrepancies between the empirical crystal formation rates in batches of experiments conducted under different ambient relative humidity conditions for each organoammonium cation. We prioritized these using a statistical model and then used the robotic system to conduct 1296 controlled interventional experiments, in which small amounts of water were deliberately introduced to the reactions. The addition of trace amounts of water promotes crystal formation for 4-methoxyphenylammonium lead iodide and iso-propylammonium lead iodide and inhibits crystal formation for dimethylammonium lead iodide and acetamidinium lead iodide. We also performed thin-film syntheses of these four materials and determined the grain size distributions using scanning electron microscopy. The addition of water results in smaller grain sizes for dimethylammonium and larger grain sizes for iso-propylammonium, consistent with earlier or delayed nucleation, respectively. The agreement between the inverse temperature crystallization and thin film results indicates that this is a feature of the organoammonium-water interaction that persists despite differences in the synthesis method. [ABSTRACT FROM AUTHOR]

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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]

Doping and alloying are valuable tools for modifying and enhancing the properties and performance of lead halide perovskites. However, the effects of heterovalent doping with Sb3+ and Bi3+ cations are still a matter of current investigation. Due to the different charge of the dopants compared to the constituting Pb2+ ions, a simultaneous creation of defects is unavoidable and the influence of these defects and the actual metal substitution become entangled. Herein, we present the first 14–15 iodido metalates, (BED)4PbE2I16 (BED=N‐benzylethylenediammonium; E=Sb (1), Bi (2)), which are model compounds for doped lead iodide perovskites and display surprisingly low band gaps of 2.01 (1) and 1.88 eV (2). Quantum chemical investigations show that this stems from a good electronic match between the PbI6 and EI6 units of the compounds. Our results provide a model system for doped perovskites, but also represent the first examples of a promising new class of metal halide materials. [ABSTRACT FROM AUTHOR]

• Lead halides deposition and conversion to perovskites by chemical vapor deposition method. • Formation of stable lead chloride iodide thin film. • Chlorine substitution by iodine during perovskite conversion step. • Perovskite thin films with micron size grains. • Improved perovskite solar cell device performance by chlorine doping. Mixed halide perovskites with chlorine (Cl) content have received significant interest due to better charge transport properties and longer diffusion length compared to pure iodine-based perovskites. The superior properties of Cl-doped perovskites improve solar cell device performance, although the quantification of Cl composition in the perovskite films remain difficult to achieve. Hence, it is difficult to correlate the Cl-quantity with the improved device performance. In this work, we deposited Cl-doped perovskite films through a facile three- and two-step sequential chemical vapor deposition (CVD) where lead halide films were deposited in the first steps of the process and subsequently converted to perovskites. No Cl substitution by iodine was observed during a sequential deposition of lead chloride and lead iodide films which reacted to form a lead chloride iodide phase (PbICl). The substitution of Cl by iodine ions only occurred during the conversion to perovskite phase. Large perovskite grains (greater than 2 µm) were realized when converting a PbI 2 film to perovskite compared to chlorine containing lead halide films, contradicting literature. However, Cl doped perovskite solar cells showed improved device efficiencies as high as 10.87% compared to an un-doped perovskite solar cell (8.76%). [ABSTRACT FROM AUTHOR]

Spin-coated films are usually polycrystalline or amorphous, while some special materials such as lead iodide (PbI2) and inorganic perovskite could be deposited onto a variety of single-crystal substrates by spin coating obtaining highly oriented films. Herein, we report an effective method for depositing highly textured PbI2 and CsPbI2Br films—via spin coating. An unexpected high-quality PbI2 film with uniform out-plane orientation of the {001} plane was deposited on the gallium nitride substrate, which was benefited from heterogeneous nucleation measured by high-resolution x-ray diffraction (XRD) and Raman mapping. Furthermore, the α-phase CsPbI2Br highly oriented film was deposited on single-crystal (100) silicon with only the (200) plane for the first time. Compressive stress was found both in PbI2 film and in CsPbI2Br film via XRD, Raman spectra, and photoluminescence spectroscopy. Density functional theory calculations were performed to confirm that CsPbI2Br had a tetragonal structure rather than an orthogonal structure. [ABSTRACT FROM AUTHOR]

To leverage the outstanding photonic qualities of lead halide hybrid perovskites under high optical irradiance, their reliability and temporal stability must be assessed. Time‐resolved scanning electron microscopy unveils that when illuminating the free surface of methylammonium lead iodide (MAPbI3) films at 500 Sun in vacuum, a giant photopotential locally develops in tens of seconds, differently evolving depending on charge‐selective substrates. It is reversible on timescales of minutes in the case of hole‐transporting poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate, while more persistent effects occurs, on the timescale of hours, in the case of electron‐transporting TiO2. In addition, films grown on TiO2 show irreversible decay of photoluminescence measured in situ and photoinduced alteration of the work function at some grain boundaries. Different responses at high irradiance are ascribable to contact‐dependent and light‐induced spatial redistribution of charged defects, either ions or localized dipoles. It is also clear that photoexcited charges play different roles in the photochemistry of systems, depending on selective contacts and they are likely to mediate diverse photoassisted redox reaction paths. The TiO2 layer may act as a photocatalyst, leading to MAPbI3 degradation and to irreversible polarization, which will hinder high‐irradiance applications. [ABSTRACT FROM AUTHOR]

Methylammonium lead iodide (MAPI) is the archetype of the intensively researched class of perovskites for photovoltaics. Nonetheless, even equilibrium aspects are far from being fully understood. Equilibrium space charge effects at the MAPI/TiO2 and MAPI/Al2O3 interfaces are discussed, which are of paramount significance for solar cells. Different from the photovoltaic literature in which such built‐in potentials are considered as being generated solely by electronic charge carriers, a generalized picture that considers the equilibrium distribution of both ionic and electronic carriers is applied. Experimental evidence is given that shows it is the ions that are responsible for the equilibrium space charge potential, the reason being a pronounced ion adsorption at the contacts. The electronic redistribution is a sheer consequence of the so‐established electric field. Experiments with mesoporous oxide as well as experiments with MAPbBr3 (MAPBr) indicate photovoltaic relevance and material generality in terms of the choice of the lead‐based perovskite. The occurrence of space charge effects at heterojunctions generated by ionic redistribution is not only a novel concept in photovoltaics, it also provides a new path to modifying charge‐selective interfaces, as well as a better understanding of the behavior in mesoporous systems. [ABSTRACT FROM AUTHOR]

Organic–inorganic hybrid lead halide perovskites have gained significant attention as light-harvesting materials in thin-film photovoltaics due to their exceptional optoelectronic properties and simple fabrication process. The power conversion efficiency of perovskite solar cells (PSCs) has surged beyond 25% in a short time span. Their transition to commercial market is a "work in progress" due to limited long-term operational stability and the persisting environmental concern due to the presence of lead. Comprehensive investigations on the interplay of material composition and interfacial effects on the device performance of PSCs based on methylammonium lead iodide have shown the crucial role of an A-site cation in incipient deterioration of the material through external stimuli (moisture, light, oxygen, or heat). Consequently, a partial or complete replacement of A-site cations by up to four isoelectronic substituents has resulted in many new perovskite compositions. The correlations between the chemical composition and the optoelectronic properties are, however, not always easy to determine. A-site cation management is governed by stability and charge neutrality of the lattice, and the choices include Cs+-cations and organic cations such as CH3NH3+ or CH(NH2)2+ and combinations thereof. Since the size of the cations is an important structural parameter, an adequate compositional engineering of the A-site could effectively optimize the stability by reducing non-radiative defect sites and enhancing carrier lifetimes. This Perspective reflects on the experimental strategies for A-site cation management and their direct impact on the stability and device performance. It also highlights the opportunities and challenges for further research and industrial commercialization of PSCs. [ABSTRACT FROM AUTHOR]

• One step solution-processed Cs 0.1 FA 0.9 PbI 3 deposition method for carbon-based PSCs. • More industrially acceptable eco-friendly solvent, DMSO via adduct approach. • High stability with no discernible decrease in efficiency for 1800 h under ambient. • Cs 0.1 FA 0.9 PbI 3 perovskite in carbon based devices exemplifies great potential of PSC. The major problem identified in carbon-based mixed cation perovskite solar cells (PSCs) is the selection of a suitable solvent for single-step solution-processed perovskite deposition in order to promote their scalable production. Herein we report a detailed study on the selection of appropriate solvent for the one-step deposition of cesium-formamidinium lead iodide (Cs 0.1 FA 0.9 PbI 3) perovskite via Lewis acid-base adduct approach for fully printable mesoporous PSCs with mesoporous TiO 2 /ZrO 2 /C architecture. Highly reproducible Cs 0.1 FA 0.9 PbI 3 solar cells were fabricated via adducts of PbI 2 with eco-friendly dimethyl sulfoxide (DMSO). The best cells fabricated with the above approach yielded a photoconversion efficiency (PCE) of 12.33% for a small area device (active area: 0.09 cm2) and 10.1% for a large area device (active area 0.7cm2). The average power conversion efficiency for 62 PSCs was found to be 10.5% under an AM 1.5G illumination. Finally, the mixed cation perovskite in carbon architecture using the Lewis acid-base adduct approach is remarkably stable, with less than 1% change from the initial PCE after 1800h of storage under dark ambient conditions (25 °C, 60–70% RH). [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]

Abstract The stability of perovskite solar cells exposed to prolonged solar irradiation is a major concern that has not been thoroughly investigated in the past. In this investigation, devices fabricated with the architecture, glass/ITO/PEDOT:PSS/MAPbI 3 /PCBM/Ag using Pb acetate as a source material, were found to operate with an efficiency of about 13%. Adding excess amounts of Pb to the precursor resulted in a presence of Pb in the perovskite (PVS) active layer. In addition, the impact of photo-induced degradation on the device efficiency was investigated. X-ray Diffraction and Time-resolved Photoluminescence analyses were used to evaluate the impact of excess Pb before and after illumination. The results indicate that changes in the crystallinity occur without any significant decrease in charge carrier lifetimes, and this is attributed to the formation of the degradation product, PbI 2. This by-product has been shown to have beneficial effects due to its influence in passivating grain boundaries and in altering the band structure at the interface between the active layer and the electron transport layer. This work demonstrates that 5 mol% excess Pb is the optimal concentration with respect to efficiency and stability of these devices. The devices can retain more than 50% of their initial efficiency after 1 h of simulated solar exposure, when compared to 0 mol% and 10 mol% excess Pb samples. Graphical abstract Schematic of passivation effect of PbI2 on grain boundaries. Image 1 Highlights • Effect of excessive Pb content in precursor materials is investigated on the stability against photo-induced degradation. • Photoluminescence studies performed reveal that excess Pb samples retain higher lifetimes after prolonged illumination. • The results are attributed to the beneficial effects from the formation of PbI 2 on the grain boundaries. [ABSTRACT FROM AUTHOR]

Organic–inorganic lead halide perovskites are highly promising materials for solar cell devices, but their widespread commercialization is hindered by their poor environmental stability. Now, porous organic cages are shown to stabilize methylammonium lead iodide films under hot and humid conditions. [ABSTRACT FROM AUTHOR]

Lead halide perovskites (LHPs) have shown remarkable promise for use in photovoltaics, photodetectors, light-emitting diodes, and lasers. Although solution-processed polycrystalline films are the most widely studied morphology, LHP nanowires (NWs) grown by vapor-phase processes offer the potential for precise control over crystallinity, phase, composition, and morphology. Here, we report the first demonstration of self-catalyzed vapor-liquid-solid (VLS) growth of lead halide (PbX2; X = Cl, Br, or I) NWs and conversion to LHP. We present a kinetic model of the PbX2 NW growth process in which a liquid Pb catalyst is supersaturated with halogen X through vapor-phase incorporation of both Pb and X, inducing growth of a NW. For PbI2, we show that the NWs are single-crystalline, oriented in the 〈1̄21̄0〉 direction, and composed of a stoichiometric PbI2 shaft with a spherical Pb tip. Low-temperature vapor-phase intercalation of methylammonium iodide converts the NWs to methylammonium lead iodide (MAPbI3) perovskite while maintaining the NW morphology. Single-NW experiments comparing measured extinction spectra with optical simulations show that the NWs exhibit a strong optical antenna effect, leading to substantially enhanced scattering efficiencies and to absorption efficiencies that can be more than twice that of thin films of the same thickness. Further development of the self-catalyzed VLS mechanism for lead halide and perovskite NWs should enable the rational design of nanostructures for various optoelectronic technologies, including potentially unique applications such as hot-carrier solar cells. [ABSTRACT FROM AUTHOR]

Methylamine lead iodide (CH3NH3PbI3), which has recently been in the spotlight as a solar cell material, has also recently shown promise for use as an active material in resistive memory cells with ultralow operation voltages, good transparencies, and flexibilities. The material’s defects, which govern its properties, differ vastly depending on the fabrication process. However, the defect chemistry is not yet entirely understood. We have therefore established a macroscopic transport model with defect-related model parameters, such as trap density, trap energy level, and Fermi level, in order to estimate these parameters for fabricated samples based on their electrical data. Our model will serve as an efficient way to analyze the properties of the active material. [ABSTRACT FROM AUTHOR]

We present a critical review of the effects of processing conditions on the morphology of methylammonium lead iodide (CH3NH3PbI3) perovskite solar cells. Though difficult to decouple from synthetic and film formation effects, a single morphological feature, specifically grain size, has been evidently linked to the photovoltaic performance of this class of solar cells. Herein, we discuss experimental aspects of optimizing the (a) temperature and time of annealing, (b) spin-coating parameters, and (c) solution temperature of methylammonium iodide (MAI) solution. [ABSTRACT FROM AUTHOR]

The inorganic cesium lead halide CsPbX 3 (where X ​= ​I, Br, Cl) are reported to possess good stability than that of organic-inorganic hybrid halides. CsPbI 3 is reported to have four phases: perovskite black phase (cubic (α), tetragonal (β), orthorhombic(γ)) and non-perovskite yellow orthorhombic (δ). With band gap of ∼ 1.73eV, CsPbI 3 -α is most suitable phase among all-inorganic lead halide Perovskites. However, in ambient atmosphere (almost instantly) the perovskite black phase convert into non-perovskite yellow orthorhombic phase. At the same time CsPbBr 3 remains in the orthorhombic phase at room temperature. Thus, in the present investigation, compositional variation of Br in Cesium lead iodide CsPbBr x I 3-x (x ​= ​0.0 to 3.0 ​at the step of 0.5) samples synthesized by cold sintering technique is studied. The XRD patterns showed the orthorhombic phase for CsPbBr 3. Further, CsPbBr x I 3-x (x ​≤ ​1.0) have shown double phase corresponding to CsPbI 3 (Pnma) ​+ ​PbI 2 (R 3 ¯ m). However, the compound with 1.5 ≤ x ​< ​3.0 showed the presence of various phases with and without oxygen including the CsPbBr 3 (orthorhombic, Pnma) phase which has also been confirmed through UV–visible spectroscopy, impedance and Schottky anomaly. This compositional failure is also suggested by deviation from Vegards law showing volumetric expansion. The role of oxygen vacancy has been probed for the compositional failure for 1.5 ≤ x ​< ​3.0 using XPS characterization and Raman spectroscopy. [Display omitted] • Compositional effect of Br in CsPbBr x I 3-x synthesized by cold sintering is studied. • x ​= ​1.5 compound showed various phases as confirmed through Schottky anomaly. • Synthesis failure at x ​= ​1.5 is investigated using impedance and microstructures. • Degradation for x ​= ​1.5 is due to excess oxygen at the grain/grain-boundary interface. • x ​= ​1.5 in CsPbBr x I 3-x do not follow Vegard's law. [ABSTRACT FROM AUTHOR]

Carbon-based hole transport material (HTM)-free perovskite solar cells have exhibited a promising commercialization prospect, attributed to their outstanding stability and low manufacturing cost. However, the serious charge recombination at the interface of the carbon counter electrode and titanium dioxide (TiO2) suppresses the improvement in the carbon-based perovskite solar cells' performance. Here, we propose a modified sequential deposition process in air, which introduces a mixed solvent to improve the morphology of lead iodide (PbI2) film. Combined with ethanol treatment, the preferred crystallization orientation of the PbI2 film is generated. This new deposition strategy can prepare a thick and compact methylammonium lead halide (MAPbI3) film under high-humidity conditions, which acts as a natural active layer that separates the carbon counter electrode and TiO2. Meanwhile, the modified sequential deposition method provides a simple way to facilitate the conversion of the ultrathick PbI2 capping layer to MAPbI3, as the light absorption layer. By adjusting the thickness of the MAPbI3 capping layer, we achieved a power conversation efficiency (PCE) of 12.5% for the carbon-based perovskite solar cells. [ABSTRACT FROM AUTHOR]

Lead halide perovskites have emerged as promising materials for various optoelectronic applications. For photovoltaics, the reference compound is the 3D perovskite (MA)PbI3 (MA+ = methylammonium). However, this material suffers from instabilities towards humidity or light. This makes the search of new stable 3D lead halide materials very relevant. A strategy is the use of intermediate size cations instead of MA, which are not suitable to form the 3D ABX3 perovskites or 2D perovskites. Here, we report on a novel 3D metal halide hybrid material based on the intermediate size cation hydroxypropylammonium (HPA+), (HPA)6(MA)Pb5I17. We will see that extending the carbon chain length from two CH2 units (in the hydroxylethylammonium cation, HEA+) to three (HPA+) precludes the formation of a perovskite network as found in the lead and iodide deficient perovskite (HEA,MA)1+xPbxI3−x. In (HPA)6(MA)Pb5I17 the 3D lead halide network results from a 2D perovskite subnetworks linked by a PbI6 octahedra sharing its faces. DFT calculations confirm the direct band gap and reveal the peculiar band structure of this 3D network. On one hand the valence band has a 1D nature involving the p orbitals of the halide. On the other, the conduction band possesses a clear 2D character involving hybridization between the p orbitals of the metal and the halide. [ABSTRACT FROM AUTHOR]

Organic-inorganic lead halide perovskite solar cells have received global attention, and their upscaling to perovskite solar modules under ambient conditions merits investigation. Herein, an upscaled mini-module consisting of five serially interconnected cells demonstrate a power conversion efficiency of 6.18% measured on an aperture area of 10.4 cm2. The perovskite photovoltaic mini-module with an inverted configuration is realized on a 5 × 5.5 cm2 ITO glass substrate using a technique combining ultrasonic spray-coating of both the NiO x hole transport layer (HTL) and perovskite photoabsorber layer with mechanical scribing for module patterning. The influence of the post-annealing duration (3, 5, 8, 10, and 15 min) of the spray-coated NiO x films under optimized fabrication conditions of the perovskite mini-module is investigated. The bulk properties of the NiO x thin films as functions of annealing time and their interfacial properties with methylammonium lead iodide (MAPbI 3) are comprehensively discussed. The use of spray-coating to assemble the NiO x HTL/perovskite photoactive layer of the mini-module demonstrate the significant potential of this technique to facilitate scalable production of perovskite-based photovoltaic modules. Image 1 • Ultrasonic spray-coated NiO x hole transport layer and perovskite films. • Mini-module with five serially interconnected cells (aperture area of 10.4 cm2). • The physical properties of the NiO x film as functions of annealing time. [ABSTRACT FROM AUTHOR]

Lead halide thin films, such as lead iodide (PbI2) and lead chloride (PbCl2), are used as precursor films for perovskite preparation, which is frequently achieved by vacuum thermal evaporation but rarely by the low-pressure chemical vapor deposition (CVD) method. Here, we report on the deposition of PbI2 and PbCl2 thin films on glass substrates by employing the low-pressure CVD method. The effect of the substrate temperature on the structure and morphology of the lead halide films is investigated. Crystalline films were realized for both lead halides, with PbI2 films showing high texture compared to the reduced texture of the PbCl2 films. Large lateral grain sizes were observed for the PbI2 films with a flat platelet grain morphology and an average grain size up to 734.2 ± 144.8 nm. PbCl2 films have columnar grains with an average grain size up to 386.7 ± 119.5 nm. The PbI2 films showed a band gap of about 2.4 eV, confirming its semiconducting properties, and the PbCl2 had a wide band gap of 4.3 eV, which shows the insulating properties of this material. [ABSTRACT FROM AUTHOR]

Cesium lead halide perovskites exhibit outstanding optical and electronic properties for a wide range of applications in optoelectronics and for light-emitting devices. Yet, the physics of the band-edge exciton, whose recombination is at the origin of the photoluminescence, is not elucidated. Here, we unveil the exciton fine structure of individual cesium lead iodide perovskite nanocrystals and demonstrate that it is governed by the electron-hole exchange interaction and nanocrystal shape anisotropy. The lowest-energy exciton state is a long-lived dark singlet state, which promotes the creation of biexcitons at low temperatures and thus correlated photon pairs. These bright quantum emitters in the near-infrared have a photon statistics that can readily be tuned from bunching to antibunching, using magnetic or thermal coupling between dark and bright exciton sublevels. The optical and electronic properties of cesium lead halide perovskite nanocrystals are dictated by the band-edge exciton, whose physics is not elucidated. Here, the authors unveil its fine structure and demonstrate that the ground dark singlet state promotes the creation of biexcitons at low temperatures and thus correlated photon pairs. [ABSTRACT FROM AUTHOR]

Lead halide perovskites possess outstanding optical characteristics that can be employed in the fabrication of phototransistors. However, due to low current modulation at room temperature, sensitivity to the ambient environment, lack of patterning techniques and low carrier mobility of polycrystalline form, investigation in perovskite phototransistors has been limited to rigid substrates such as silicon and glass to improve the film quality. Here, we report on room temperature current modulation in a methylammonium lead iodide perovskite (MAPbI3) flexible transistor made by an extremely cheap and facile fabrication process. The proposed phototransistor has the top-gate configuration with a lateral drain–channel–source structure. The device performed in the linear and saturation regions both in the dark and under white light in different current ranges according to the illumination conditions. The transistor showed p-type transport characteristics and the field effect mobility of the device was calculated to be ~1.7 cm2 V−1 s−1. This study is expected to contribute to the development of MAPbI3 flexible phototransistors. [ABSTRACT FROM AUTHOR]