CH3NH3PbI3 Crystals Research Articles

Colloidal Synthesis of Air-Stable CH3NH3PbI3 Quantum Dots by Gaining Chemical Insight into the Solvent Effects

Because of the superior optical properties and potential applications in display technology, colloidal synthesis of halide perovskite quantum dots has been intensively studied. Although great successes have been made in the fabrication of green emissive CH3NH3PbBr3 quantum dots, the fabrication of stable iodide-based CH3NH3PbI3 quantum dots remains a great challenge because of their sensitivity to moisture in the open air. Even in a glovebox, the colloidal CH3NH3PbI3 quantum dots obtained from N,N-dimethylformamide suffer from instability caused by fast degradation within days to weeks. In this work, we investigated the interactions between perovskite precursors and various polar solvents as well as their influence on the crystallization of CH3NH3PbI3 in reprecipitation synthesis. By gaining chemical insight into the coordination effects, we can explain the degradation of CH3NH3PbI3 to the defective crystals with coordinated solvents on the surface and/or intrinsic inner iodine vacancies. On the basis of ...

Synergy of ammonium chloride and moisture on perovskite crystallization for efficient printable mesoscopic solar cells

Organometal lead halide perovskites have been widely used as the light harvester for high-performance solar cells. However, typical perovskites of methylammonium lead halides (CH3NH3PbX3, X=Cl, Br, I) are usually sensitive to moisture in ambient air, and thus require an inert atmosphere to process. Here we demonstrate a moisture-induced transformation of perovskite crystals in a triple-layer scaffold of TiO2/ZrO2/Carbon to fabricate printable mesoscopic solar cells. An additive of ammonium chloride (NH4Cl) is employed to assist the crystallization of perovskite, wherein the formation and transition of intermediate CH3NH3X·NH4PbX3(H2O)2 (X=I or Cl) enables high-quality perovskite CH3NH3PbI3 crystals with preferential growth orientation. Correspondingly, the intrinsic perovskite devices based on CH3NH3PbI3 achieve an efficiency of 15.6% and a lifetime of over 130 days in ambient condition with 30% relative humidity. This ambient-processed printable perovskite solar cell provides a promising prospect for mass production, and will promote the development of perovskite-based photovoltaics.

Construction of high performance CH3NH3PbI3-based solar cells by hot-casting technique

Two-dimensional plane CH3NH3PbI3 crystals in millimeter size have been first successfully constructed on FTO glass coated with mesoporous TiO2 by hot-casting technique. Depending on the closely and continuous arrangement of large perovskite crystals in the film, a best power conversion efficiency (PCE) of 16.01% was achieved along with a photocurrent density of 21.32mA/cm2, an open circuit voltage of 1.07V and a fill factor of 0.70 from the corresponding CH3NH3PbI3-based solar cells with p-i-n structure. Even more exciting was the quite good stability of the hot-casting-based device, which remained at more than 91% under 55% humidity for 10 days.

Perovskite CH3NH3PbI3 crystals and films. Synthesis and characterization

Synthesis of organometal halide perovskite CH3NH3PbI3 has received much attention recently because of promising photosensitive properties usable for solid state solar cell (SSSC). Here the crystals of tetragonal phase (I4/mcm, a =8.8743Å, c =12.6708Å) of CH3NH3PbI3 were prepared. Formation of the CH3NH3PbI3 crystals was controlled by the SEM, EDS, XRD and Raman spectroscopy. Optical characteristics of the crystals were obtained using PL spectrometry and spectral ellipsometry methods. PL spectra of orthorhombic phase of CH3NH3PbI3 crystals were recorded the first time. Taking into account the practice use, the CH3NH3PbI3 films are obtained via the sol–gel method with “spin-on” coating of CH3NH3PbI3 sol. The films are 500nm in thickness and exhibit an openwork structure. Such a structure is optimal for SSSC construction because it increases the surface contact area between CH3NH3PbI3 and p-conductor.

CH3NH3PbI3, A Potential Solar Cell Candidate: Structural and Spectroscopic Investigations.

Hybrid organic-inorganic metal halides of the type CH3NH3PbX3 have emerged as potential materials for photovoltaic applications. In this paper we discuss structural, electronic, and optical spectroscopy investigations performed on high quality single crystals of CH3NH3PbI3. Our results conclusively suggest that CH3NH3PbI3 crystallizes in centrosymmetric space group and the methylammonium moiety exhibits disordered packing at room temperature. Extracted values of the exciton binding energy, the electron-phonon coupling constant, and the schematic energy level diagram constructed from the emission broadening, Raman, and photoemission spectroscopy measurements clearly show the potential of this system in photovoltaic applications.

Shape-Evolution Control of hybrid perovskite CH3NH3PbI3 crystals via solvothermal synthesis

We systematically synthesized CH3NH3PbI3 crystals using solvothermal process, and the reaction conditions such as concentration of the precursor, temperature, time, and lead source have been comprehensively investigated to obtain shape-controlled CH3NH3PbI3 crystals. The results showed that the CH3NH3PbI3 crystals exhibit tetragonal phase and the crystals change from nanoparticles to hopper-faced cuboids. Photoluminescence spectra of the crystals obtained with different lead sources show a blue shift due to the presence of defects in the crystals, and the peak intensity is very sensitive to the lead sources. Moreover, impurities (undesirable byproducts and excess components like HI or CH3NH2) presented during crystal growth can result in hopper growth.

Crystal Engineering for Low Defect Density and High Efficiency Hybrid Chemical Vapor Deposition Grown Perovskite Solar Cells

Synthesis of high quality perovskite absorber is a key factor in determining the performance of the solar cells. We demonstrate that hybrid chemical vapor deposition (HCVD) growth technique can provide high level of versatility and repeatability to ensure the optimal conditions for the growth of the perovskite films as well as potential for batch processing. It is found that the growth ambient and degree of crystallization of CH3NH3PbI3 (MAPI) have strong impact on the defect density of MAPI. We demonstrate that HCVD process with slow postdeposition cooling rate can significantly reduce the density of shallow and deep traps in the MAPI due to enhanced material crystallization, while a mixed O2/N2 carrier gas is effective in passivating both shallow and deep traps. By careful control of the perovskite growth process, a champion device with power conversion efficiency of 17.6% is achieved. Our work complements the existing theoretical studies on different types of trap states in MAPI and fills the gap on the theoretical analysis of the interaction between deep levels and oxygen. The experimental results are consistent with the theoretical predictions.

CH3NH3PbI3 crystal orientation and photovoltaic performance of planar heterojunction perovskite solar cells

The effect of crystal orientation of CH3NH3PbI3 on photovoltaic properties has rarely been studied due to the lack of method to fabricate perovskite films with well-controlled crystal orientation in specific direction. Here, we have controlled the orientation of CH3NH3PbI3 crystal by changing organic precursors (CH3NH3I and CH3NH3Cl) and successfully fabricated highly oriented CH3NH3PbI3 crystals with two different orientations to the substrate. When we investigated the effect of crystal orientation on photovoltaic performance using the films with two different crystal orientations, we have realized that the crystal orientation of perovskite is directly related to power conversion efficiency (PCE). The PCE difference due to different crystal orientation is interpreted by the charge transfer lifetime. Faster charge transfer from perovskite layer to charge transport layer exhibits higher JSC and PCE.

Filling perovskite (5-AVA)y(CH3NH3)1−yPbI3 or (5-AVA)y(CH3NH3)1−yPbI3−xClx halide in a 3D gel framework for multi-deformable perovskite solar cell

Application-specific requirements for future perovskite solar cells include lightweight, mechanical resilience, and deformability for multi-purpose utilizations ranging from electronic skin and implant in the body to wearable textiles. Here we demonstrate the experimental realization of intrinsically bendable, stretchable, twistable, and compressible perovskite solar cells made by adsorbing hole-transporting polyaniline, solvothermal-processed halide (5-AVA)y(CH3NH3)1−yPbI3 or (5-AVA)y(CH3NH3)1−yPbI3−xClx precursor as well as electron-transporting [6,6]-phenyl-C61-butyric acid methyl with three-dimensional amphiphilic gel matrix. The multi-deformable perovskite solar cell with CH3NH3PbI3 crystals yields a power conversion efficiency of 3.62% at undeformed state and AM1.5G sunlight irradiation, while the efficiency can increase to 4.51% at a bending angle of 140°, to 4.46% at an elongation of 220%, to 5.10% at a twist angle of 360°, and to 5.57% at a compression ratio of 80%. After hundreds of arbitrary deformations, the solar cell still remains ~130% efficiency. Owing to an amphiphilic surface, the solar cell is relatively stable for 7 days when exposed in 78%-humidity ambient air. This work represents a significant step forward, as it realizes the solvothermal synthesis of halide CH3NH3PbX3 (X=I, Cl) precursors and low-temperature fabrication, arbitrary deformations without sacrificing power conversion efficiency along with promising humidity-resistance in ambient atmosphere for perovskite solar cells.

Investigation on the high pressure annealing induced re-crystallization mechanism of CH3NH3PbI3 film

In this paper, high pressure annealing induced re-crystallization mechanism of CH3NH3PbI3 film has been investigated by SEM, UV–vis absorption spectra, and X-ray diffraction (XRD), respectively. CH3NH3PbI3 crystals, which were annealed under the pressure of 6 kPa at 100 °C for 80 min, were oriented at the same direction on the surface of the mesoporous Polypropylene (PP) film. These PP/CH3NH3PbI3 composite films exhibited different light-harvesting capabilities over the visible to near-IR. The evolution of the intensity ratio I110/I220 and I220/I310 of CH3NH3PbI3 annealed at 100 °C for different annealing time under the same pressure of 6 kPa has been also investigated in detail. Compared with the film prepared via the traditional method, the high pressure annealing induced CH3NH3PbI3 film showed better stability in moderate humid environmental condition (25% RH).

CH3NH3PbI3: precise structural consequences of water absorption at ambient conditions.

The crystal structure of the pristine (I) and aged (II) crystals of CH3NH3PbI3 (hereafter MAPbI3) hybrid organic-inorganic lead iodide has been studied at 293 K with high-precision single-crystal X-ray diffraction using a synchrotron light source. We show that (I) and (II) are characterized by an identical tetragonal unit cell but different space groups: I422 for (I) and P42212 for (II). Both space groups are subgroups of I4/mcm, which is widely used for MAPbI3. The main difference between (I) and (II) comes from the difference in hydrogen bonds between the MA+ cation and the PbI3 framework which is the direct consequence of H2O insertion in the aged crystal (II).

Perovskite CH3NH3PbI3(Cl) Single Crystals: Rapid Solution Growth, Unparalleled Crystalline Quality, and Low Trap Density toward 10(8) cm(-3).

Single crystal reflects the intrinsic physical properties of a material, and single crystals with high-crystalline quality are highly desired for the acquisition of high-performance devices. We found that large single crystals of perovskite CH3NH3PbI3(Cl) could be grown rapidly from chlorine-containing solutions. Within 5 days, CH3NH3PbI3(Cl) single crystal as large as 20 mm × 18 mm × 6 mm was harvested. As a most important index to evaluate the crystalline quality, the full width at half-maximum (fwhm) in the high-resolution X-ray rocking curve (HR-XRC) of as-grown CH3NH3PbI3(Cl) single crystal was measured as 20 arcsec, which is far superior to so far reported CH3NH3PbI3 single crystals (∼1338 arcsec). The unparalleled crystalline quality delivered a low trap-state density of down to 7.6 × 10(8) cm(-3), high carrier mobility of 167 ± 35 cm(2) V(-1) s(-1), and long transient photovoltaic carrier lifetime of 449 ± 76 μs. The improvement in the crystalline quality, together with the rapid growth rate and excellent carrier transport property, provides state-of-the-art single crystalline hybrid perovskite materials for high-performance optoelectronic devices.

Mesoporous BaTiO3/TiO2 Double Layer for Electron Transport in Perovskite Solar Cells

We report on the effect of BaTiO3/TiO2 mesoporous double layer (MDL) in the electron transport layer (ETL) of perovskite solar cells and enhancement of the photovoltaic performance. The conversion efficiency was enhanced from 9.89% for TiO2 mesoporous single layer (MSL) to 12.4% for BaTiO3/TiO2 MDL. The CH3NH3PbI3 crystal size on the BaTiO3/TiO2 MDL was larger. The larger CH3NH3PbI3 crystals resulted in the better light absorption and improved JSC. Moreover, VOC was also improved by suppressing a charge recombination, which is attributable to the fewer CH3NH3PbI3 crystal boundaries and band structure of BaTiO3/TiO2 MDL. The results suggest that using BaTiO3 as the second layer of the TiO2 mesoporous layer is a promising way to boost the performance of perovskite solar cells.

Perovskite Photodetectors based on CH3 NH3 PbI3 Single Crystals.

As very important light-harvesting materials, organic-inorganic perovskites have showed an alluring prospect in optoelectronic devices. However, most of the perovskite devices, such as photodetectors reported recently, are based on the polycrystalline films of perovskites, and the large grain boundaries and amounts of defects existing in films are unfavorable for the further improvement of device performance. Herein, high-quality single crystals of CH3 NH3 PbI3 were successfully prepared through a simple solution immersing method. The obtained CH3 NH3 PbI3 crystals showed the morphologies of nanowires and nanoplates, which were confirmed to belong to the same tetragonal phase. Both nanowire- and nanoplate-based photodetectors exhibited improved performance over CH3 NH3 PbI3 polycrystalline thin films, with an on/off ratio approaching 103 , which is one of the highest values reported so far for perovskite photodetectors.

Orientation of Organic Cations in Hybrid Inorganic–Organic Perovskite CH3NH3PbI3 from Subatomic Resolution Single Crystal Neutron Diffraction Structural Studies

We report the crystal growth of well-faceted single crystals of methylammonium lead iodide, CH3NH3PbI3, and detailed single crystal neutron diffraction structural studies aimed at elucidating the orientation of the methylammonium (CH3NH3+) cation in the tetragonal and cubic phases of the hybrid inorganic–organic perovskite. Room temperature experiments reveal a tetragonal structure where the protonated amine substituent (−NH3+) of the cation is disordered in four positions, each preferentially located near the neighboring iodine of the [PbI6] octahedra, while the methyl substituent (−CH3) is disordered in eight positions located near the body position of the unit cell. High temperature experiments show a cubic structure where the cation aligns along the [011] (edge), the [111] (diagonal), and the [100] (face) directions of the unit cell. The resulting site occupancy ratio suggests the CH3NH3+ cation resides primarily along the [011] direction, in agreement with reported DFT calculations. One important fea...

Role of Ferroelectric Nanodomains in the Transport Properties of Perovskite Solar Cells

Metropolis Monte Carlo simulations are used to construct minimal energy configurations by electrostatic coupling of rotating dipoles associated with each unit cell of a perovskite CH3NH3PbI3 crystal. Short-range antiferroelectric order is found, whereas at scales of 8-10 nm, we observe the formation of nanodomains, strongly influencing the electrostatics of the device. The models are coupled to drift-diffusion simulations to study the actual role of nanodomains in the I-V characteristics, especially focusing on charge separation and recombination losses. We demonstrate that holes and electrons separate into different nanodomains following different current pathways. From our analysis we can conclude that even antiferroelectric ordering can ultimately lead to an increase of photoconversion efficiencies thanks to a decrease of trap-assisted recombination losses and the formation of good current percolation patterns along domain edges.

ペロブスカイト太陽電池へのITO透明電極スパッタリング直接堆積の影響

Thin film solar cells using perovskite materials are very intensively studied since the perovskite materials such as CH3NH3PbI3 crystal have been found to show sensitizing effects on a TiO2 electron transport layer. This class of solar cell has made tremendous progress during the last few years, leading to a recently certified record power conversion efficiency (PCE) of 21.02%. In the perovskite /crystalline-Si (c-Si) tandem solar cell, furthermore, the theoretical value of PCE is expected as large as 35 %. Toward this application, the perovskite solar cell must be highly transparent at near-infrared wavelengths so that sufficient light is transmitted to the narrow-bandgap bottom cell. In this study, we fabricated the organic-lead halide perovskite solar cells comprising a transparent sputtered indium tin oxide (ITO) top electrode. We observed the PCE of 1.5% in transparent perovskite solar cells with a thin molybdenum oxide buffer layer and ITO electrode. Moreover, we obtained the PCE of 2% even in solar cells with ITO electrode sputtered directly on the organic charge transport layer. The photovoltaic property could be confirmed under the light irradiation from the ITO top electrode side.

Efficient Perovskite Hybrid Photovoltaics via Alcohol‐Vapor Annealing Treatment

In this work, alcohol‐vapor solvent annealing treatment on CH3NH3PbI3 thin films is reported, aiming to improve the crystal growth and increase the grain size of the CH3NH3PbI3 crystal, thus boosting the performance of perovskite photovoltaics. By selectively controlling the CH3NH3I precursor, larger‐grain size, higher crystallinity, and pinhole‐free CH3NH3PbI3 thin films are realized, which result in enhanced charge carrier diffusion length, decreased charge carrier recombination, and suppressed dark currents. As a result, over 43% enhanced efficiency along with high reproducibility and eliminated photocurrent hysteresis behavior are observed from perovskite hybrid solar cells (pero‐HSCs) where the CH3NH3PbI3 thin films are treated by methanol vapor as compared with that of pristine pero‐HSCs where the CH3NH3PbI3 thin films are without any alcohol vapor treatment. In addition, the dramatically restrained dark currents and raised photocurrents give rise to over ten times enhanced detectivities for perovskite hybrid photodetectors, reaching over 1013 cm Hz1/2 W−1 (Jones) from 375 to 800 nm. These results demonstrate that the method provides a simple and facile way to boost the device performance of perovskite photovoltaics.

Transition from the Tetragonal to Cubic Phase of Organohalide Perovskite: The Role of Chlorine in Crystal Formation of CH3NH3PbI3 on TiO2 Substrates.

The role of chlorine in the superior electronic property and photovoltaic performance of CH3NH3PbI(3-x)Clx perovskite has attracted recent research attention. Here, we study the impact of chlorine in the perspective of the crystal structure of the perovskite layer, which can provide important understanding of its excellent charge mobility and extended lifetimes. In particular, we find that in the presence of chlorine (PbCl2 or CH3NH3Cl), when CH3NH3PbI3 films are deposited on a TiO2 mesoporous layer instead of a planar TiO2 substrate, a stable cubic phase rather than the commonly observed tetragonal phase is formed in CH3NH3PbI3 perovskite at room temperature. The relative peak intensity of two major facets of cubic CH3NH3PbI3 crystals, (100)C and (200)C facets, can also be easily tuned, depending on the film thickness. Furthermore, compared with pristine CH3NH3PbI3 perovskite films, in the presence of chlorine, CH3NH3PbI3 crystals grown on planar substrates exhibit strong preferred orientations on (110)T and (220)T facets.

Collective Behavior of Molecular Dipoles in CH3NH3PbI3

Using ab initio molecular dynamics, we report a detailed exploration of the thermal motion occurring in perovskite crystals of the formula CH3NH3PbI3. We exploit the data generated to obtain estimates of the rotational relaxation time of the cation CH3NH3+. We examine the tetragonal and cubic phases, as both may be present under operational conditions. Influenced by each other, and by the tilting of PbI6 octahedra, cations undergo collective motion as their contribution to polarization does not vanish. We thereby qualitatively describe the modus operandi of formation of microscopic ferroelectric domains.