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Single‐crystal hybrid perovskites represent an emerging class of next‐generation semiconductors due to their excellent and tunable optoelectronic properties, along with a solution‐based, low‐temperature growth process. 2D single‐crystal hybrid perovskites are especially promising as their long‐range ordered multiple quantum well structure induces many peculiar properties, such as large exciton binding energy, large in‐plane conductivity, and improved environmental stability, which make them suitable for low‐dimensional optoelectronics applications and fundamental studies. Herein, the structural properties, morphology, and optoelectronic behavior of 2D thin film phenethylammonium lead iodide (PEA2PbI4) single‐crystals, synthesized using the space‐confined growth technique are explored. A planar device is fabricated and its spectral photoresponse is studied under broadband supercontinuum white light. Remarkably, the device exhibits an ultra‐low dark current (10−14 A), indicative of low defect density and suppressed ion migration. Under white light, the current increases linearly with the incident power, up to a factor of 105, and the device achieves a specific detectivity of 109 Jones. The temperature and wavelength dependence of the photocurrent suggests the dissociation of excitons as one of the main mechanisms affecting photoconduction. Furthermore, stability under air exposure and illumination turns out to be remarkable. [ABSTRACT FROM AUTHOR]

Developing efficient photoactive and environmentally stable methylammonium lead iodide (CH3NH3PbI3, MAPI) perovskite films in open-air conditions is challenging. This can be achieved by incorporating inorganic nanostructures into the MAPI perovskites. Recently, various shapes of inorganic nanostructures like PbS, CdS, and SnS have been included, but the effect of nanocuboids shapes has not been explored. In the present study, we studied the impact of adding PbS nanocuboids to MAPI perovskite. We found that incorporating these chemically grown PbS nanocuboids significantly improves MAPI perovskite material's optoelectronic properties. The PbS nanocuboids were synthesized using different concentrations of CTAB complexing agent. Then, using slot die coating, thin films of MAPI:PbS nanocomposite were prepared with different-sized PbS nanocuboids. With the incorporation of PbS nanocuboids, significant improvements have been observed in the optoelectronic properties of MAPI perovskite films. Finally, we fabricated pristine MAPI and MAPI:PbS nanocomposite-based photodetectors using a slot die coating on a TiO2-coated FTO substrate. Compared to pristine perovskite, the photodetector fabricated with the incorporation of 20% of PbS in MAPI (MAPI:PC-2) has the shortest decay time of 0.08 s and four-fold improvements in photosensitivity and the highest photodetectivity of 108.11 × 108 Jones with an external quantum efficiency of ~ 13.77%. We believe the enhanced optical absorption and efficient charge collection between the perovskite and hole transport layer may be responsible for the improved photodetector performance. These results suggest that incorporating PbS in MAPI perovskite holds promise for various optoelectronic applications. [ABSTRACT FROM AUTHOR]

Detailed investigation has been performed for the effect of in-situ substrate heating on the growth of printed perovskite films towards getting high performance perovskite solar cells (PSCs). Perovskite layers and charge transport layers were printed by slot die method. The perovskite layers were printed in two steps, where first lead iodide (PbI2) films were printed and then methyl ammonium iodide (MAI) ink was printed on them to convert PbI2 into methyl ammonium lead iodide (MAPbI3) perovskite. For the controlled growth of PbI2 crystals the printed PbI2 films were in-situ heated at different temperatures like 50oC, 70oC and 90oC that resulted in formation of compact films with different crystal growths and phases, which affected the growth of perovskite crystals thereafter. It was difficult to convert the compact PbI2 films completely into MAPbI3 by one time printing of MAI, therefore the idea of multiple print cycles of MAI was implemented. The optimized print cycles of MAI led to achieve complete conversion of PbI2 into high quality MAPbI3 crystals, which resulted in PSCs having champion power conversion efficiency (PCE) up to 11.99%. The steady state PCE of the optimized cell did not exhibit any decay for > 200 s. Under continuous 1 sun illumination of a tungsten-halogen lamp, the optimized cells retained over 50% of their initial efficiency for up to ∼ 300 h. Subsequently, the solar modules printed with optimum print conditions in 9 cm × 13 cm area with an active area of 64.8 cm2, exhibited PCE of 7.77%. [ABSTRACT FROM AUTHOR]

Lead iodide (PbI2) is a 2D layered semiconductor used in several electronic applications, such as solar cells, X-ray, and gamma-ray detectors. Most of its properties have been reported for monocrystals or polycrystalline thick films used in high-energy photon detectors. As for thin films used in other optoelectronic devices, the reported properties are limited to the conditions adopted in manufacturing the devices. Furthermore, very little is known about the properties of films deposited by sputtering. Here, we investigate the optical and structural properties of PbI2 thin films deposited by rf-sputtering a PbI2 target. The deposition temperature significantly influences the film's properties, as determined by X-ray, scanning electron microscopy (SEM), atomic force microscopy (AFM), UV-vis, and Raman spectroscopy. A common characteristic at all temperatures was forming metallic lead (Pb) segregated in the surface of films, with concentration depending on the deposition temperature. These lead clusters were successfully converted into PbI2 using an iodination process, allowing the synthesis of pure PbI2 films without lead segregation. The activation energy for the reaction between Pb clusters and iodine vapor was determined by adopting the Arrhenius equation. It was also observed that converting PbI2 film into perovskite through the two-step process, by immersion of the PbI2 film into methylammonium iodide solution, transforms the segregated lead into perovskite. The sputtering technique allows the deposition of uniform films over large areas compatible with roll-to-roll processes, which are desired to produce large-area detectors and perovskite solar cells.

Methylammonium Lead Iodide (MAPbI3) has often been known to have a perovskite content and is widely employed in Perovskite Solar Cells (PSCs). However, PSCs suffer from rapid degradation due to their low stability and sensitivity to light, heat, humidity, and air. Hence, this project proposes a two-step spin coat method to synthesize MAPbI3 perovskites in an ambient condition using two different types of solvent (DMF only and a mixture of DMF and DMSO) which were prepared to examine the quality of the perovskite layer. The thin films were characterized to study the structural, optical properties, and surface morphology using XRD, UV-Vis spectroscopy, and SEM. The XRD results show that the perovskite layer prepared using a mixture of DMF and DMSO has a better crystallinity than DMF, even after the sample was kept for two days as the principal peaks confirm the complete formation of MAPbI3 perovskite film. UV-Vis showed that the perovskite layer prepared with the mixture of DMF and DMSO as the solvent has a higher absorbance than the perovskite layer prepared with DMF. The surface morphology of the MAPbI3 films consists of the formation of cubical crystals of uniform size with high compactness, as confirmed by the SEM analysis. However, after two days, both samples showed a degradation providing feedback on the occurred transition to PbI2 due to the contact with moisture and thermal stability. Moreover, the better stability of perovskite films was observed by a two-step than one-step process was demonstrated with comparatively good reproducibility. [ABSTRACT FROM AUTHOR]

We report continuous wave laser-assisted evaporation (CLE), a thin film deposition technique that yields phase-pure and stoichiometric thin films of halide perovskites (HaPs) from stoichiometric HaP targets. We use methylammonium lead bromide (MAPbBr3) to demonstrate the ability to grow with CLE well-oriented and smooth thin films on various substrates. Further, we show the broader applicability of CLE by preparing films of several other 3D HaP compounds, viz., methylammonium lead iodide, formamidinium lead bromide, and a 2D one, butylammonium lead iodide. CLE is a single-source, solvent-free, room-temperature process that needs only roughing pump vacuum; it allows the deposition of hybrid organic-inorganic compound films without needing post-thermal treatment or an additional organic precursor source to yield the intended product. The resulting films are polycrystalline and highly oriented. All these features, and the fact that one stoichiometric source serves as the target, make for an attractive, potentially scalable dry deposition approach. [ABSTRACT FROM AUTHOR]

The use of hybrid halide Perovskites is helping us get closer to our aim of completely selfsufficient structures in terms of energy production. Preparation of a device of photoactive material CH3NH3PbI3 {FTO (Fluorine-doped tin Oxide)/CH3NH3PbI3/Spiro-OMeTAD/Al} for the photovoltaic applications has been described in this article. Producing a homogeneous thin film through the use of lower temperature, processedsolution devices with one-step spin coating processes is an essential stage in the fabrication process. To generate the thin films on the FTO-substrate, the one-step spin coating approach was utilized for the deposition of the precursor solution, which consisted of methylammonium iodide and lead iodide in a molar ratio of 3:1. This technique was employed to prepare the thin films. The FESEM technique was utilized to carry out the investigation of the surface morphology of this thin layer. In addition, the essential parameters of this device, like barrier height, saturation current, current density, ideality factor, carrier mobility, resistance, carrier lifetime, and capacitance have been computed using current-voltage (I-V) characteristics and the impedance spectroscopy technique. A laser with a power of 20 milliwatts and a wavelength of 532 nanometers was used to light the gadget. The current conduction mechanism exhibits ohmic behavior at a low voltage, while at medium voltages, TFSCLC is the mechanism that regulates charge transportation. Despite the fact that TCSCLC is demonstrated at higher voltages. The TCSCLC model was used to conduct an investigation of the hole's mobility. [ABSTRACT FROM AUTHOR]

Perovskites have emerged as a forerunner of electronics research due to their vast potential for optoelectronic applications. The numerous combinations of constituent ions and the potential for doping of perovskites lead to a high demand to track the underlying electronic properties. Solution‐based electrochemistry is particularly promising for detailed and facile assessment of perovskites. Here, electrochemical impedance spectroscopy (EIS) of methylammonium lead iodide (MAPbI3) thin films is performed and model them with an equivalent circuit that accounts for solvent, ionic, and thin film effects. A dielectric constant consistent with prior AC studies and a diffusion constant harmonious with cation motion in MAPbI3 are extracted. An electrical double layer thickness in the perovskite film of 54 nm is obtained, consistent with lithium doping in perovskite films. Comparing the EIS and equivalent circuit model of perovskite films to control ITO‐only data enabled the assignment of the ions at each interface. This comparison implied a double layer of primarily lithium ions inside the perovskite film at the solution interface with significant recombination of ions on the solution side of the interface. This demonstrates EIS as a powerful tool for studying the fundamental charge accumulation and transport processes in perovskite thin films. [ABSTRACT FROM AUTHOR]

Evaporation of perovskite thin films for solar cell applications is a solvent‐free, well controllable, and scalable deposition path with promising prospects for commercialization. Compared to commonly applied simultaneous co‐evaporation of various halide precursor salts, sequential evaporation followed by an annealing step allows to better control the amount of deposited precursors, and has the potential to largely improve reproducibility. In this work, Cs/formamidinium (FA)‐based lead iodide perovskites are deposited via sequential evaporation in a vacuum chamber and the phase formation and evolution of different precursor‐stacking sequences and annealing conditions are investigated with in situ X‐ray diagnostics. In addition, some Br is added to investigate the effect of halide intermixing. The stacking sequence is found to strongly influence the formation of dominant phases as well as the preferential orientation and HGHmorphology of the as‐deposited films. These variations in turn affect the diffusion and conversion during thermal annealing and ultimately the conversion ratio of the final perovskite layers. For example, it is found that starting the stacking sequences with the A cations (CsI, FAI) favors a fast and complete conversion of the perovskite phase. However, the result is the formation of perovskite layers with large voids. [ABSTRACT FROM AUTHOR]

Photovoltaic cells based on metal‐halide perovskites have exceeded the performance of other thin film technologies and rival the performance of devices based on archetypical silicon. Attractively, the perovskite active layer can be processed via a variety of solution‐ and vapor‐based methods. Herein, emphasis is on the use of vapor transport codeposition (VTD) to process efficient n–i–p photovoltaic cells based on methylammonium lead iodide (MAPbI3). VTD utilizes a hot‐walled reactor operated under moderate vacuum in the range of 0.5–10 Torr. The organic and metal‐halide precursors are heated with the resulting vapor transported by a N2 carrier gas to a cooled substrate where they condense and react to form a perovskite film. The efficiency of photovoltaic devices based on VTD‐processed MAPbI3 is found to be highest in films with excess lead iodide content, with champion devices realizing exceeding 12%. [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]

Ionic liquids (ILs) have found widespread use in controlling the crystallization process of perovskites, optimizing the morphology and enhancing the device performance, especially in the one-step method. However, research regarding the effects of ionic liquids on perovskite devices prepared using the two-step method remains relatively scarce. Here, an IL 1-Hexyl-3-methylimidazolium Tetrafluoroborate (HMIMBF4) is selected as an additive in the perovskite precursor solution for the fabrication of PSCs using the two-step method. Our study involves a systematic exploration of the precise effects of ILs on the morphology of perovskite thin films, defect density, and photovoltaic performance. IL HMIMBF4 is convincingly shown to possess a robust chemical affinity with perovskite components, thereby establishing a basis for the inhibition of ion migration. Concurrently, ILs play a pivotal role in governing the morphology of perovskite while also facilitating the conversion of lead iodide into the perovskite structure. Benefiting from the regulation of the perovskite morphology and defect states by IL HMIMBF4, the devices with an efficiency exceeding 23% is ultimately achieved. Our research provides a comprehensive comprehension and contributes to advancing the utilization of ILs in two-step photovoltaic devices. [ABSTRACT FROM AUTHOR]

Herein, a synthesis method for obtaining lead iodide through chemical bath deposition, a type of chemical solution deposition without the use of organic solvents, is presented; the process consists of three stages. In the first stage, tin hydroxide films are produced which act as a seed layer allowing for a better adherence of the film that is to be deposited. The second stage consists of the synthesis of the lead iodide films. Finally, annealing is done (100, 150, and 200 °C) with the purpose of promoting the polytypic transitions of the material and to study the effect of these structures on the properties of the material. Assessment of the structural and optical properties of the films is done by means of scanning electron microscopy, X‐ray diffraction, X‐ray photoelectron spectroscopy, optical spectroscopy, Raman spectroscopy, and transmission electron microscopy, where a direct influence of the annealing in the induction of polytypes is observed. The resultant PbI2 films have a large‐area coverage across the substrate, wide‐bandgap (2.38 eV), and a structure that belongs to the 2H and 4H polytypes. Hence, it is suggested from these results that the chemically deposited PbI2 thin films are promising candidates for large‐area optoelectronic applications. [ABSTRACT FROM AUTHOR]

Thin films made of formamidinium lead iodide (FAPbI3) perovskites prepared by a two-step sequential deposition method using various solvents for formamidinium iodide (FAI) - isopropanol, n-butanol and tert-butanol, were studied with the aim of finding a correlation between morphology and solvent properties to improve film quality. They were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM) and their photophysical properties were studied by means of absorption and photoluminescence (PL) spectroscopies. XRD patterns, absorption and PL spectra proved α-phase formation for all selected solvents. An excessive amount of PbI2 found in perovskite films prepared with n-butanol indicates incomplete conversion. Thin film morphology, such as grain and crystallite size, depended on the solvent. Using tert-butanol, thin films with a very large grain size of up to several micrometers and with preferred crystallite orientation were fabricated. The grain size increased as follows: 0.2–0.5, 0.2–1 and 2–5 µm for isopropanol, n-butanol and tert-butanol, respectively. A correlation between the grain size and viscosity, electric permittivity and polarizability of the solvent could be considered. Our results, including fabrication of perovskite films with large grains and fewer grain boundaries, are important and of interest for many optoelectronic applications. [ABSTRACT FROM AUTHOR]

The incorporation of a spacer cation to improve the stability of lead halide perovskites entails a trade-off, notably compromising film quality and device performance, particularly in quais-2D variants employing a higher proportion of hydrophobic, larger spacer cations. Addressing this challenge in quasi-2D perovskite-based devices requires enhancement in film morphology, crystallinity, and vertical orientation to optimize charge transport. Herein, we present a simple one step spin coating synthesis approach for producing PEA 2 MA n-1 Pb n I 3n+1 (n = 5–2) thin films from a single precursor solution. Notably, our method operates at room temperature without the need of usually toxic anti-solvent or specialized additives, resulting in high quality crystalline films that are vertically oriented and smooth. We systematically investigate the impact of annealing processes on crystal structure, including gradient annealing (GA) as well as thermal annealing at 100℃ for durations of 10 and 15 minutes. Our findings indicate that the films with n = 4 exhibits superior crystallinity and vertical crystallographic orientation, alongside reduced roughness, and minimal contamination of the lower n mixtures. Gradient annealing notably enhances the crystallinity of n = 3 films. While the surface of all the films appears smooth with flake-like structure, the n = 2 sample notably exhibits pitting. [Display omitted] • Oreinted quai-2D (PEA) 2 MA n-1 Pb n I 3n+1 perovskites achieved by robust one step process without anti-solvent. • The hydrophobic PEA molecule enhances the stability of quasi-2D perovskites. • The vertical orientation and highest crystallinity are achieved for (PEA) 2 MA 3 Pb 4 I 13. • Enhanced stability and reduced degradation in vertically oriented (PEA) 2 MA n-1 Pb n I 3n+1 quasi-2D perovskites. [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]

Perovskites have been in the spotlight in the field of solar cells due to their high efficiency and their low cost of materials and fabrication processes. Perovskite solar cells (PSCs) have shown an efficiency of up to 25%. Nevertheless, PSCs have some drawbacks such as rapid degradation in ambient conditions. To improve PSC stability, lead is usually replaced with bismuth. In this article, we report the results when doping the methylammonium lead iodide (CH3NH3)PbI3, aka MAPbI3, with different bismuth quantities. The incorporation of bismuth into the lattice leads to a remarkable change in optoelectronics and morphological structure. Substituting lead atoms with 2% bismuth improves some characteristics of MAPbI3 layers, such as removing pinholes and increasing crystallite size and optical absorption. Furthermore, bismuth doping improves the stability of pure MAPbI3 layers, which after 4 weeks exhibits higher degradation compared to bismuth-doped MAPbI3 samples, which remain stable after that period. [ABSTRACT FROM AUTHOR]

Electrospray deposition technique has been reported previously for fabricating effective and stable perovskite thin film, leading to efficient perovskite solar cells. In this work, a comprehensive investigation of the formation mechanism of methylammonium lead iodide perovskite (CH 3 NH 3 PbI 3) film by electrospray technique is demonstrated and compared to the formation mechanism through the conventional spin coating technique. In the electrospray process, charged MAI nanoparticles are gradually introduced onto the PbI 2 film, intercalating within the PbI 2 structure to produce the perovskite film. In contrast, the spin-coating method involves supplying the MAI solution in bulk, leading to perovskite crystal formation through the dissolution of the PbI 2 layer by the MAI solution, followed by recrystallization into perovskite oriented in the [110] direction, 30° inclined to the substrate. The impact of charge and the electric field on the formation of perovskite film using the electrospray is explored. Furthermore, the intrinsic stability of perovskite films is monitored in real-time in a highly humid environment (≥80 % relative humidity (RH)) using in-situ Grazing Incidence Wide Angle X-ray Scattering (GIWAXS), and a degradation mechanism is proposed to enhance the durability of the perovskite-based devices. The study further delves into the comparison of the stability of electrosprayed and spin-coated perovskite film, and the impact of humidity level and the presence of a hole-transporting layer on the stability of the perovskite layer. Overall, this work provides a detailed understanding of the formation and humidity-induced degradation mechanism of electrosprayed perovskite films, offering insights that can extend to various applications of perovskite materials. [Display omitted] • Formation mechanism of CH 3 NH 3 PbI 3 perovskite using electrospray is described and compared to the spin-cated perovskite. • In electrospray, perovskite formation occurs through CH 3 NH 3 I intercalation into PbI 2 film • In spin coating, formation occurs through dissolution recrystallization. • CH 3 NH 3 PbI 3 perovskite degrades through the formation of perovskite hydrate leading to form lead iodide. • Electrosprayed perovskite is highly stable compared to spin-coated perovskite. [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]

Organometallic halide-based perovskite solar cells have played a significant role in the development of photovoltaic technology. The synthesis of the perovskite usually needs specific atmospheres, especially controlled humidity. Here, we demonstrate the synthesis of compact methylammonium lead iodide perovskite (MAPbI3) on TiO2 under ambient conditions through one and two-step spin-coating deposition methods, which both resulted in an unconverted PbI2 on the films. The two-step method provided a higher amount of PbI2 regarding the reaction of methyl ammonium iodide (MAI) with an outer layer of the first bonded PbI2 hindered the inner layer to interact with MAI. The Ostwald ripening (OR) process that was applied to the thin film resulted through one-step deposition synthesis has successfully converted the unformed PbI2 to MAPbI3 with a more uniform, lower void, and higher crystal size as confirmed by XRD and SEM analysis results. The application of MAPbI3 prepared using OR treatment in the solar cell resulted in higher efficiency (7.64%) than the one synthesized without OR (4.91%). [ABSTRACT FROM AUTHOR]

Thin films of methylammonium lead iodide (MAPbI3) were deposited on glass slides under various preparation conditions by a two-step dip-coating method, using dip-coated lead iodide (PbI2) thin films as the underlying layer. The dip-coating method used involved immersion of a slowly rotating substrate in the required solution. The PbI2 film was immersed into methylammonium iodide (MAI) solution in 2-propanol for 10–60 min. The MAPbI3 films were thermally annealed at 85 °C for 10–30 min. Fundamental properties of the annealed MAPbI3 films were studied by x-ray diffraction (XRD), scanning electron microscopy (SEM) and ultraviolet-visible spectrophotometry. The XRD patterns and SEM micrographs revealed single tetragonal-phase structure, with diffraction peaks became intense and narrow with increasing dipping times and upon thermal annealing. Transmittance spectra of these MAPbI3 film/glass systems declined steeply near 780 nm , equivalent to a bandgap energy of 1.55 eV , assigned to the MAPbI3 with optical absorption coefficient of 10 5 cm - 1 . [ABSTRACT FROM AUTHOR]

Controlling the microstructure of hybrid halide perovskite thin films is essential for optimizing their performance in optoelectronic devices. It is well established that the strain state of the perovskite layer affects its stability. Likewise, the orientation of the perovskite lattice is a determining parameter as these materials have shown pronounced anisotropies in their physical and mechanical properties. In this work, the authors focus on the understanding of the mechanisms that govern the strain and texture observed in MAPbI3 thin films deposited on various oxide substrates. A thorough study of the evolution of the strain of the perovskite layer upon cooling down to room temperature from the crystallization temperature (100 °C) shows an essentially relaxed behavior of the perovskite layers. This result contradicts the commonly accepted hypothesis according to which MAPbI3 layers synthesized above ambient temperature are strained due to the large mismatch in the thermal expansion coefficients of the perovskite and its substrate. The texture in MAPbI3 layers is investigated by means of synchrotron full‐field diffraction X‐ray microscopy. This technique allows the direct observation of the [hh0] and [00l]‐oriented domains at the origin of the observed textures, demonstrating both their twin and ferroelastic nature. The stability of the different domain orientations is investigated by DFT calculations, illustrating the determining role of the chemical environment at the film‐substrate interface. PbI2‐ terminated surfaces are found to favor the [hh0] orientations while for MAI‐terminated ones, both [hh0] and [00l] domains are equally stabilized. The different results constitute an important step of clarification and understanding from the perspective of controlling the microstructure of perovskite layers. [ABSTRACT FROM AUTHOR]

Controlling the crystallinity, homogeneity, and surface morphology is an efficient method of enhancing the perovskite layer. These improvements contribute toward the optimization of perovskite film morphology for its use in high-performance photovoltaic applications. Here, different solvents will be used in order to process the perovskite precursor, to improve the interfacial contacts through generating a smooth film and uniform crystal domains with large grains. The effect that the solvent has on the optical and structural properties of spin-coated methyl ammonium lead iodide (MAPbI3) perovskite thin films prepared using a single-step method was systematically investigated. The spin-coating parameters and precursor concentrations of MAI and PbI2 were optimized to produce uniform thin films using the different solvents N, N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and γ-butyrolactone (GBL). The effect that the solvent has on the morphology of the MAPbI3 films was examined to determine how the materials can be structurally altered to make them highly efficient for use in perovskite hybrid photovoltaic applications. Scanning electron microscopy (SEM) and X-ray diffractometry (XRD) results show that the synthesized MAPbI3 films prepared using DMSO, DMF, and GBL exhibit the best crystallinity and optical characteristics (photoluminescence (PL)), respectively, of the prepared films. The optical properties resulting from the noticeable improvement PL of the films can be clearly correlated with their crystallinity, depending on the solvents used in their preparation. The film prepared in DMSO shows the highest transmittance and the highest bandgap energy of the prepared films. [ABSTRACT FROM AUTHOR]

Amongst the different perovskites being investigated for application in solar cells, one of the most frequently scrutinized is methylammonium lead iodide CH3NH3PbI3 (or MAPbI3), which is usually obtained by the reaction of lead iodide (PbI2) with methylammonium iodide (MAI). Although this perovskite has been extensively studied and utilized in the manufacture of high-efficiency solar cells, its formation chemistry is still not well understood. Reliable experimental determination of the activation energy between PbI2 and MAI has been difficult due to the rapid reaction at room temperature. In this work, we determined the activation energy by adopting the Arrhenius equation. This was possible by controlling the reaction using MAI vapor, instead of liquid solution. This procedure allowed the reaction to be carried out at temperatures of up to 150 °C. The formation of MAPbI3 films was obtained by a two-step process: deposition of thin PbI2 film by thermal evaporation and subsequent conversion into perovskite by exposure to MAI vapor. The conversion of PbI2 to MAPbI3 as a function of temperature was probed by X-ray diffraction. An activation energy of 0.12 ± 0.02 eV was obtained. This low value explains the ease of MAPbI3 formation at low temperatures, and partially explains its instability in environmental conditions. [ABSTRACT FROM AUTHOR]

Solvent engineering by Lewis‐base solvent and anti‐solvent is well known for forming uniform and stable perovskite thin films. The perovskite phase crystallizes from an intermediate Lewis‐adduct upon annealing‐induced crystallization. Herein, it is explored the effects of trimethyl phosphate (TMP), as a novel aprotic Lewis‐base solvent with a low donor number for the perovskite film formation and photovoltaic characteristics of perovskite solar cells (PSCs). As compared to dimethylsulfoxide (DMSO) or dimethylformamide (DMF), the usage of TMP directly crystallizes the perovskite phase, i.e., reduces the intermediate phase to a negligible degree, right after the spin‐coating, owing to the high miscibility of TMP with the anti‐solvent and weak bonding in the Lewis adduct. Interestingly, the PSCs based on methylammonium lead iodide (MAPbI3) derived from TMP/DMF‐mixed solvent exhibit a higher average power conversion efficiency of 19.68% (the best: 20.02%) with a smaller hysteresis in the current‐voltage curve, compared to the PSCs that are fabricated using DMSO/DMF‐mixed (19.14%) or DMF‐only (18.55%) solvents. The superior photovoltaic properties are attributed to the lower defect density of the TMP/DMF‐derived perovskite film. The results indicate that a high‐performance PSC can be achieved by combining a weak Lewis base with a well‐established solvent engineering process. [ABSTRACT FROM AUTHOR]

The effects of dimensional structure on the properties of lead iodide perovskite (C8H9NH3)2(CH3NH3)n−1PbnI3n+1 were investigated. Furthermore, perovskite thin films with different dimensionalities were applied as the channel layer of thin film transistors (TFT). The electrical performance and stability of TFT devices were significantly improved through the regulation of dimensional microstructure of the perovskites. As a result, the quasi-2D (n = 6) perovskite TFTs achieved a field-effect mobility (μFE) of 3.90 cm2 V−1 s−1, with 104 on-off current ratio and −1.85 V threshold voltage, which can be maintained well after 4 days without degradation at 30% ambient humidity. Moreover, the electrical performance of the TFTs based on Pure-2D and Quasi-2D perovskite also exhibited a good bias stability. [ABSTRACT FROM AUTHOR]

Complex phenomena are prevalent during the formation of materials, which affect their processing-structure-function relationships. Thin films of methylammonium lead iodide (CH3NH3PbI3, MAPI) are processed by spin coating, antisolvent drop, and annealing of colloidal precursors. The structure and properties of transient and stable phases formed during the process are reported, and the mechanistic insights of the underlying transitions are revealed by combining in situ data from grazing-incidence wide-angle X-ray scattering and photoluminescence spectroscopy. Here, we report the detailed insights on the embryonic stages of organic-inorganic perovskite formation. The physicochemical evolution during the conversion proceeds in four steps: i) An instant nucleation of polydisperse MAPI nanocrystals on antisolvent drop, ii) the instantaneous partial conversion of metastable nanocrystals into orthorhombic solvent-complex by cluster coalescence, iii) the thermal decomposition (dissolution) of the stable solvent-complex into plumboiodide fragments upon evaporation of solvent from the complex and iv) the formation (recrystallization) of cubic MAPI crystals in thin film. Complex phenomena are prevalent during the formation of materials, and they affect the processing structure-function relationship. Here the authors elucidate the stochastic transformation processes happening during the spin coating of perovskite colloidal precursors by multimodal characterization. [ABSTRACT FROM AUTHOR]

• Elastic modulus determination of perovskite thin film using nanoindentation. • Experimental results are corroborated by density functional theory calculations. • No quasi-2D perovskite observed in mixed 2D-3D perovskites. • Elastic Modulus of 2D perovskite is less than half of the modulus of 3D perovskite. • Elastic modulus of the mixed perovskite is close to the lower bound for the mixture. The stiffness of the perovskite active layer plays a critical role in influencing the flexibility of a solar cell. This is one of the important parameters which must be considered while deciding the architecture of the flexible device. Till now, there have been limited studies on the mechanical properties of 2D and 3D perovskite thin films. In this study, we report the very first time, the elastic modulus of the most commonly used 3D perovskite i.e. methylammonium lead iodide (MaPbI 3), the pure 2D perovskite (5-AVA) 2 PbI 4 which is based on 5-aminovaleric acid (5-AVA) cation as well as the 2D-3D mixed perovskites thin films through nanoindentation technique. The elastic modulus for the 3D perovskite has been found to be around 16.5 GPa, while it decreases to 6.3 GPa for pure 2D perovskite. The experimental results have also been corroborated by density functional theory calculations done for the 2D and 3D perovskite. The 2D perovskite shows a much lower modulus than the 3D perovskite and can be used within a 2D-3D mixture for improving the mechanical flexibility of the active layer. Also, it is well established that 2D perovskites are much more stable against moisture as compared to their 3D counterparts due to the presence of hydrophobic organic alkyl ammonium cation. Thus, the device containing an active layer comprising of a mixture of 3D and 2D perovskite can be used to improve the environmental stability of the overall device in addition to achieving mechanical durability. [ABSTRACT FROM AUTHOR]

Semiconducting perovskite thin films are cheap to fabricate and can be coated on fluorine-doped tin oxide (FTO) substrates by using simple techniques such as the solution deposition method. In this work, we show that the improved electrical performance of perovskite film produces that of single crystals in an ambient atmosphere. Herein, Methylammonium Lead Chloride Iodide (MAIPbCl 2) is played as perovskite films, which were composited with different weight percent (wt%) of rGO from 7 to 10. All samples in this work were presented with physicochemical, electrical, and optical properties. However, the challenge of this work is the electron scattering at the grain boundaries as a result of the double schottky barrier. The best decreasing the double schottky barrier yielded a maximum conductivity of 68.72 ± 0.95 S/cm, a low sheet resistance of 5.47 ± 1.64 Ω, a decrease in the lowest oxygen vacancy, and an increase in the grain size from 27.89 nm (of MAIPbCl 2) to 34.96 nm at room temperature for the MAPbCl 3 -8 wt% rGO composite, which also revealed that this strategy significantly helped to improve the performance of the film. Furthermore, temperature dependence for MAIPbCl 2 -rGO composites demonstrates this high electrical conductivity from room temperature to 323 K, with highest electrical conductivities of 78.68 ± 0.01 S/cm and the activation energy of 0.18 eV at 313 K for 8 wt% rGO. Therefore, MAIPbCl 2 -rGO composite films demonstrated the enhancement of performance of MAIPbCl 2 films; this is next promising for perovskite films in the future. [ABSTRACT FROM AUTHOR]

The study focuses on to examine the effect of CdS-based electron transport layer on the performance of perovskite solar cell. Based on the novel device architecture, CdS was fabricated using chemical bath deposition at different time interval of 10, 20, and 30 min. However, the perovskite layer was prepared by two-step spin coating technique in order to achieve better structural properties. The analyzed perovskite solar cell shows a very good power conversion efficiency of 11.69%, Jsc 15.4 mA/cm2, Voc of 1.0 V, and FF of 0.75 for the device structure CdS/CH3NH3PbI3/Spiro-OMeTAD for CdS grown for 10 min. Finally, the study discusses on various factors like effect of microstrain, dislocation density, and series resistance on the photovoltaic performance of perovskite solar cells. [ABSTRACT FROM AUTHOR]

Crystallization and morphology of perovskite film played an important role to obtain efficient performance of perovskite solar cells. This study is aimed at optimizing the fabrication of hybrid organic–inorganic lead iodide perovskite layer by a two-step method modified by a double dip coating process which enables to control the perovskite crystallization and morphology. The duration time of each circle for the step of dipping PbI2 film to methylammonium iodide solution was varied from 90 to 240 second. The obtained perovskite films were characterized by X-ray diffraction to evaluate the transformation of PbI2 reactant to the perovskite product and its crystallization, by scanning electron microscopy to observe its morphology. Then, the perovskite films were implemented in functional perovskite solar cell devices followed by current–voltage characterization. Results showed that the perovskite was formed via an equilibrium process which reached an optimum transformation of PbI2 to the product after 2 × 150 second circle dip coating, and its morphology was smooth with the least voids. The solar cell devices fabricated at the optimum conditions achieved a comparable performance of about 14%. [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]

This study describes the metastability properties of lead iodide (PbI2) thin films which were deposited by thermal chemical vapor deposition (CVD) and spin coating on ultrasonically and chemically cleaned microscope glass substrates. Morphological differences due to deposition techniques were defined by scanning electron microscopy (SEM). Deposited PbI2 thin films have been exposed to laboratory atmosphere ambient, vacuum, and enhanced deionize water vapor (EDIWV) in order to define metastability changes. Samples metastability changes have been investigated by current–voltage (I–V), time-dependent conductivity, and annealing cycle method depending on atmospheric conditions. Activation energy of PbI2 thin films was calculated from temperature-dependent dark conductivity. Based on results gathered from this work, degradation of PbI2 dependent on atmospheric condition and surface morphology with the aspect of meta/instability view has been tried to analyzed. [ABSTRACT FROM AUTHOR]

The influence of the precursor solution temperature (40 °C, 50 °C, 70 °C and 90 °C) on the crystalline nature of the mixed halide methyl ammonium lead iodide perovskite (MAPI) thin films grown using one-step deposition method is investigated. Precursor solution used is a combination of Lead chloride, Lead iodide and Methyl ammonium iodide at a composition of 1:1:4 in Dimethylformamide. Better crystallinity (> 70%) and largest crystallite size (~ 76 nm) are observed in the thin films prepared with solution temperature at 40 °C and 70 °C, respectively. Two different mechanisms that are responsible for better crystallinity and growth of crystallite in the perovskite thin films under study are identified. The observed variation in crystallinity is attributed to the amount of formation of solvent-induced intermediate phase in thin films, as evidenced from the presence of XRD peak at 7.4°. The formation of intermediate phase controls the otherwise fast and uncontrolled crystallization of perovskites to produce better crystalline nature. Variation in the crystallite size is attributed to the nature of the growth of intermediate compound, Methyl ammonium lead chloride, which determines the possibility of template-assisted growth of MAPI. This study emphasizes the critical role of the formation of intermediate phase along with the template-assisted growth in the fabrication of highly crystalline perovskite thin films with large crystallite/grain size that are indispensable for the fabrication of efficient devices. [ABSTRACT FROM AUTHOR]

All‐inorganic perovskite materials are attractive alternatives to organic–inorganic perovskites because of their potential for higher thermal stability. Although CsPbI3 is compositionally stable under elevated temperatures, the cubic perovskite α‐phase is thermodynamically stable only at >330 °C and the low‐temperature perovskite γ‐phase is metastable and highly susceptible to non‐perovskite δ‐phase conversion in moisture. Many methods have been reported which show that the incorporation of acid (aqueous HI) or "HPbI3"—recently shown to be dimethylammonium lead iodide (DMAPbI3) —lowers the annealing temperature required to produce the black, perovskite phase of CsPbI3. Herein, the optical and crystallographic data presented show that dimethylammonium (DMA) can successfully incorporate as an A‐site cation to replace Cs in the CsPbI3 perovskite material. This describes the stabilization and lower phase transition temperature reported in the literature when HI or HPbI3 is used as precursors for CsPbI3. The Cs–DMA alloy only forms a pure‐phase material up to ≈25% DMA; at higher concentrations, the CsPbI3 and DMAPbI3 begin to phase segregate. These alloyed materials are more stable to moisture than neat CsPbI3, but do not represent a fully inorganic perovskite material. [ABSTRACT FROM AUTHOR]

Formamidinium lead iodide (CH(NH2)2PbI3, FAPI) thin films have been deposited on glass substrates at 150 °C using ambient pressure aerosol assisted chemical vapour deposition (AACVD). The films have been analysed by a range of techniques including powder X-ray diffraction (pXRD), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, and UV–Vis–NIR absorption spectroscopy. Sharp reflections in the pXRD pattern can be indexed to the α-phase of FAPI which confirms the crystallinity of the as-deposited film and reveals a preferred growth orientation along the (002) plane with respect to the substrate. High magnification SEM images show that the thin film is comprised of a network of intimately connected FAPI crystallites which form a mesoporous architecture. EDX mapping of lead and iodine emission peaks show that the Pb and I within these films are spatially co-localised. Optical measurements show as-deposited FAPI films have absorption onsets in the near infra-red with a direct bandgap value of 1.46 eV, suitable for single junction solar cells. Four-point probe measurement of as deposited films show that the electrical conductivity (σ) of the FAPI thin film is 5.2 × 10–7 S/cm, which is similar to FAPI thin films deposited by spin coating technique. [ABSTRACT FROM AUTHOR]

An upscalable chemical vapor deposition setup has been built‐up and employed in producing methylammonium lead iodide (MAPI) thin film perovskite solar cells, leading to a maximum efficiency of 12.9%. The method makes use of methylamine gas and hydrogen iodide gas to transform a predeposited layer of lead(II)iodide (PbI2) into MAPI. Although the reaction mechanism includes the intermediate phases lead oxide (PbO) and lead hydroxide (Pb(OH)2), indicated at least on the surface of the samples by XPS, neither species could be observed in XRD measurements of the stepwise reaction, which show a mixture of highly oriented cubic and tetragonal MAPI perovskite lattice systems. [ABSTRACT FROM AUTHOR]

In the present work, we have fabricated and characterized in the development of methylammonium lead iodide (CH3NH3PbI3) perovskite-based hole transport layer (HTL)-free photodiode with configuration (FTO|CH3NH3PbI3|PC60BM{[6,6]-phenyl-C60-butyric acid methyl ester}|Al. The one-step spin coating technique has been used for the deposition of the precursor solution including methylammonium iodide and lead iodide with molar ratio 3:1 to prepare the perovskite thin films onto FTO-substrate. The elemental study has been done by EDX spectroscopy. Furthermore, surface morphology of CH3NH3PbI3 thin film has been characterized with the importance of photovoltaic parameters such as charge carrier mobility, saturation current, and barrier height, by I(V) measurements. The expected rectification and photo response behavior has been analyzed from energy level diagram of the materials. The device demonstrates good photo response and exhibits saturation current in the value of 4.5 × 10–4 mA and mobility of 5.27 × 10–4 cm2 V–1 s–1, respectively. Moreover, the charge carrier lifetime has been calculated of 7.81 × 10–4 s by electrochemical impedance spectroscopy (EIS). [ABSTRACT FROM AUTHOR]

Methylammonium lead iodide (CH3NH3PbI3 or MAPbI3) is one of the hybrid perovskite materials most widely used in high performing perovskite solar cells. In this work, the charge carrier recombination process of MAPbI3 perovskite thin-film fabricated on corning 1737 glass substrate is studied by means of transient photocurrent measurements and the current decay curves after turning off the lights. The influences of temperature (25–70 °C), illumination time (30–90 s) and intensity of illumination (100–1000 W m−2) on the photocurrent response are studied. The photocurrent measurements are taken in vacuum to avoid the effect of atmospheric air and moisture, at an applied field of 100 V cm−1. The MAPbI3 film shows good photosensitivity with two orders of magnitude change in current when exposed to full intensity of light. As soon as the light is turned on, the current increases rapidly; however, a small decrease is observed before a stabilized current is achieved. The stabilized value of current does not depend upon exposure time. The current falls abruptly as soon as the light is turned off and then slowly reaches back the dark current value. The fast decay of photocurrent can be attributed to fast recombination of free electrons and hole having decay time constant approximately 100 ms and the slow decay corresponds to slow re-emission of trapped carriers which has at least 3–4 times higher decay time constants compared to the fast decay. Intensity-dependent photocurrent follows a power law (Iph~ Φγ), indicating predominantly bimolecular recombination process. The activation energy (Ea) estimated from the temperature-dependent dark current measurement is found to be ~ 210 meV. [ABSTRACT FROM AUTHOR]

Air‐stable inorganic cesium lead iodide (CsPbI3) perovskite thin films with a bandgap of 1.7 eV are a promising candidate for tandem cell solar cells, comprising a perovskite top cell with a crystalline silicon bottom cell. The device design and simulations are important to develop high‐efficiency photovoltaic devices. However, knowledge of complex optical constants of the CsPbI3 thin films is mandatory to complement such tasks. Herein, air‐stable inorganic CsPbI3 perovskite thin films are prepared using one‐step synthesis through a spin‐coating method. Variable angle spectroscopic ellipsometry (VASE) is then conducted at five angles (43.9°, 48.9°, 53.9°, 58.9°, and 63.9°) to obtain ellipsometric data (Ψ and Δ). The thickness nonuniformity model of the perovskite thin film combined with an effective medium approximation for describing rough surface is adopted to achieve excellent fitting. The complex optical constants of the CsPbI3 thin film are experimentally obtained in the wavelength range of 300–1200 nm. The present results open the door for design and simulations on high‐efficiency CsPbI3/c‐Si tandem solar cells. [ABSTRACT FROM AUTHOR]

The efficiency and photocurrent density reported for p‐type‐sensitized solar cells up to now are still lagging behind that of the n‐type counterparts, limiting the successful development of p–n tandem cells. To circumvent this issue, NiO thin film is fabricated by the aerosol‐assisted chemical vapor deposition (AACVD) technique and used in p‐type solar cells. A systematic study is conducted to comprehend the correlation between NiO thickness and the power conversion efficiency (PCE) of liquid‐state NiO‐based sensitized solar cells. By carefully designing the cell components, this type of device demonstrates the highest photocurrent density (Jsc) exceeding 18 mA cm−2 when using iodine/triiodide as the redox shuttle matching the one produced by the TiO2 counterpart. This is accomplished by 1) using the AACVD technique for the one‐step deposition of compact and mesoporous NiO electrodes, 2) optimizing the thickness of the NiO layer through controlling the deposition time, and 3) adopting methylammonium lead iodide (CH3NH3PbI3) as a light harvester prepared via a sequential deposition method. [ABSTRACT FROM AUTHOR]

Chloride is extensively used in the preparation of metal halide perovskites such as methylammonium lead iodide (MAPbI3–xClx), but its persistence and role in solution‐processed materials has not yet been rationalized. Multiple‐source vacuum deposition of perovskites enables a fine control over thin‐film stoichiometry and allows the incorporation of chemical species irrespective of their solubility. Herein, the first example of mixed MAPbI3–xClx thin films prepared by three‐source vacuum deposition is presented using methylammonium iodide (MAI), PbI2, and PbCl2 as precursors. The optoelectronic properties of the material are evaluated through photovoltaic and electro‐/photoluminescent characterizations. Besides the very similar structural and optical properties of MAPbI3 and MAPbI3–xClx, an increased electroluminescence efficiency, longer photoluminescence lifetimes, as well as larger photovoltage, are observed in the presence of chloride, suggesting a reduction of nonradiative charge recombination. [ABSTRACT FROM AUTHOR]

Lead iodide, PbI2, is one of the promising metal halide materials used for x- and γ-ray detection; it is also a key constituent of organometallic halide perovskites for low-cost solar cells. Here, we report a mature technology for the fabrication of microelectronic devices—an electron beam evaporation method to prepare highly uniform PbI2 thin films with a size of up to 10 cm × 10 cm on various rigid and flexible substrates at room temperature; the fabricated x-ray detectors show a consistent detection performance. The detection performance of the PbI2 thin film based flexible detectors demonstrate high robustness and stability under various bending states, suggesting themselves as potential candidates for the development of next-generation, large-area, and flexible x-ray detecting devices by using pure PbI2 films. [ABSTRACT FROM AUTHOR]

Here we demonstrate a low-temperature process for the synthesis of pinhole-free lead iodide and perovskite (CH3NH3PbI3) films. The approach consists in converting amorphous sputtered lead sulfide films onto lead iodide (PbI2) films through an iodination process. The following step consists of the conversion of PbI2 into CH3NH3PbI3 through dipping into methylammonium iodide (CH3NH3I) solution. The effectiveness of this new route was investigated through X-ray diffraction, optical transmittance, scanning electron microscopy and X-ray photoelectron spectroscopy. This method is comprehensibly compatible with large-scale and large-area deposition and provides a convenient and highly reproducible route for the preparation of perovskite thin films. [ABSTRACT FROM AUTHOR]

Lead iodide is one of the best room temperature radiation detector including applications in solar cell and photodetectors. Herein, we have fabricated the high-quality thin films of pure and Nd:PbI2 through a simple and cost-effective spin-coating route and investigated their key properties. X-ray diffraction study confirms the growth orientation of all films along c-axis/(001) plane and single phase of 2H-PbI2 Polytypes with the crystallites of size in range of 21–31 nm. Further confirmation of growth and phase was carried out through FT-Raman analysis. EDX and SEM mapping was also carried out to confirm the Nd doping and its homogeneity in the films. SEM provides a clear view on the surface morphology of grown films and grain size was found in the range of 54–71 nm. Optical measurement shows high transparency, i.e., ~ 90% for grown films in visible to NIR region. The direct bandgap is observed to be enhanced with Nd doping from 2.45 to 2.58 eV; however, there is another bandgap which shows reduction with doping from 2.30 to 2.24 eV. This shows the possibility of existence of sub-energy bandgap in PbI2. The stable value of refractive index is evaluated ~ 2. The value of εʹ is found to varies from 4 to 27 in the energy range of 1–2.5 eV. Optical limiting behavior of all films was also studied at two lasers of λ = 532 nm and 632.8 nm. Moreover, a device fabrication was done for electrical study and found the resistivity increases from 5.14 × 108 Ω-cm for pure to 1.18 × 109 Ω-cm for 5% Nd-doped PbI2. [ABSTRACT FROM AUTHOR]

Organometallic halide perovskites have attracted great research interest as light‐active materials for use in optoelectronics. Here, we report a high‐performance photoconductor based on a methylammonium lead iodide (MAPbI3) film that was prepared from a methylamine‐treated MAPbI3/PbI2 perovskite film. An ultrahigh responsivity of 3.6 A W−1 and detectivity of 5.4×1012 Jones were obtained for the film under 0.5 mW cm−2 white‐light illumination. In addition, under 420 nm light irradiation, the film exhibited its highest responsivity and detectivity of 30 A W−1 and 2.4×1014 Jones, respectively. The excellent photo‐response performance results from the improved electronic quality and suppressed nonradiative recombination channels of the treated perovskite thin film. [ABSTRACT FROM AUTHOR]

In this work, XRD and some optical parameters of porous PbI2 thin films were investigated. Various thicknesses of lead iodide thin films were prepared by fast thermal evaporation technique (TET). X-ray diffraction patterns showed diffraction peaks before and after annealing at the orientations (001), (002), (202), (003) and (220) at 2=12.6°, 25.4°, 38.8°, 41.6° and 52.2°, respectively. Scherrer analysis indicated that grain size extends from about 8 to 18 nm. Scan electron microscopy (SEM) revealed high porosity of PbI2 thin films. UV-vis spectroscopy and diffusive reflectivity have been used to calculate the optical bandgap. The two methods indicate that the PbI2 prepared by TET has a direct optical bandgap (about 2.5 eV) with Urbach tail width of the order 0.76 eV. [ABSTRACT FROM AUTHOR]

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Highlights • This experimental work reports refractive index, extinction coefficients, and dielectric functions at different incident angles in visible range for the first time. • The refractive index of CsPbI 3 thin film is 2.46 at 435 nm. • Microstructure of the cubic phase Pm-3 m was investigated by X-ray diffraction. • CsPbI 3 thin film showed the sharp absorption edge and PL emission near infrared region with direct band gap of 1.67 eV with high color purity of red emission. Abstract This experimental work reports refractive index, extinction coefficients, and dielectric functions at different incident angles in visible range for the first time. The refractive index of CsPbI 3 thin film is 2.46 at 435 nm with this result implies that Cs based lead halide solar cells may be, ideal antireflection coating for many tandem solar cells. Thus lower refractive index of CsPbI 3 inorganic perovskite material is beneficial for perovskite device fabrications because of the minimum light looses to reflection at the front of the active layer. Furthermore microstructure of the cubic phase Pm-3 m was investigated by X-ray diffraction. CsPbI 3 perovskite thin film showed the sharp absorption edge and PL emission near infrared region with direct band gap of 1.67 eV with high color purity of red emission. In addition, the higher dielectric function value of CsPbI 3 , will helps to many optoelectronic devices. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

Static anti-solvent treatment is rarely employed for perovskite thin film fabrication, even though this method is dependent only on fewer thin film growth parameters as compared to the dynamic anti-solvent application. Thus, studies on the influence of static anti-solvent treatment on the properties of perovskite thin films is important to gain insight to the growth processes, which is very scarce as well. In this study, we investigate the static anti-solvent treatment to tailor the morphology of Lead Iodide (PbI 2) thin films for the fabrication of precursor-free Methylammonium Lead Iodide (MAPI) perovskite thin films through the two-step deposition method using Chlorobenzene as an anti-solvent. Remarkable influence of the anti-solvent loading time on the film morphology of PbI 2 and MAPI thin films is observed. The crystallinity of PbI 2 decreases upon increasing the anti-solvent loading time. A complete conversion of the precursors to MAPI along with the largest grain size are attained even at short loading times, ∼5s. Grain size does not increase considerably at higher loading times. Linear absorption studies on MAPI thin films show an increase in the Urbach energy with an increase in the loading time, which indicates an increase in the defect density. The increase in defect density with anti-solvent loading time is attributed to the concurrent decrease in the crystallinity of the PbI 2 thin film. Steady-state and time-resolved photoluminescence (PL) studies performed on the MAPI thin films show highest PL intensity and life time at an optimum anti-solvent loading time (∼5s), which arises due to the trade off between largest grain size and lowest defect density. These observations not only highlights the need for an optimum crystallinity in the PbI 2 thin films for the fabrication of superior quality MAPI thin films but also infers an optimum static anti-solvent loading time as the increase in grain size and life time enhances the device performance while an increase in defect density degrades the performance. [Display omitted] • Static anti-solvent treatment is employed in two-step fabrication of MAPI thin films. • Crystallinity of PbI 2 thin film decreased upon increasing anti-solvent loading time. • Anti-Solvent loading time governs grain size and defect density in MAPI thin films. • MAPI thin films show larger grains and highest lifetime at optimum loading time. • Study asserts the need of optimum PbI 2 crystallinity for superior MAPI thin films. [ABSTRACT FROM AUTHOR]