The hybrid halide perovskite CH$_3$NH$_3$PbI$_3$ is easy to manufacture and inexpensive. Despite these, its efficiency as a solar cell is comparable to today's efficient solar cells. For these reasons, it is attracting a lot of attention today. However, the effects of the CH$_3$NH$_3^+$ (MA) molecule in the perovskite structure on the electronic and structural properties are still a matter of debate. Previous studies have generally focused on the rotation of the MA molecule. In this study, from a different perspective, the effects of the movement of the MA molecule along the C-N axis are investigated. With this method, the effects of the MA molecule were examined in a more controlled way. In this study, density functional theory (DFT) that accounts for van der Waals (vdW) interactions was used in the calculations for the cases. According to the data obtained, H-I ionic bonds are formed between the MA molecule and the inorganic framework. Within the structure, the H-I bond length tends to be preserved, although the position of the MA changes. In this mechanism, the I ion plays an important role by moving away from its place in the Pb-I-Pb alignment. The position of the I ion determines the nature of the band gap transition. Another effect is on the value of the band gap. Depending on the position of the I ion, the band gap may narrow by about 0.26 eV. The separation of the I ion from the Pb-I-Pb alignment by the effect of the MA molecule breaks the inverse symmetry. According to the data obtained from this study, this mechanism in the band gap is due to the breaking of the inverse symmetry in the crystal structure.
CH3NH3PbI3-based solar cells were characterized with electron beam-induced current (EBIC), and compared to CH3NH3PbI3-xClx ones. A spatial map of charge separation efficiency in working cells shows p-i-n structures for both thin film cells. Effective diffusion lengths, LD, (from EBIC profile) show that holes are extracted significantly more efficiently than electrons in CH3NH3PbI3, explaining why CH3NH3PbI3-based cells require mesoporous electron conductors, while CH3NH3PbI3-xClx ones, where LD values are comparable for both charge types, do not.
Methylammonium lead iodide, as related organometal halide perovskites, emerged recently as a particularly attractive material for photovoltaic applications. The origin of its appealing properties is sometimes assigned to its potential ferroelectric character, which remains however a topic of intense debate. Here, we rationalize from first-principles calculations how the spatial arrangement of methylammonium polar molecules is progressively constrained by the subtle interplay between their tendency to bond with the inorganic framework and the appearance of iodine octahedra rotations inherent to…
Methylammonium lead triiodide (CH3NH3PbI3) perovskite solar cell is a gem in the list of photovoltaic semiconductors. Although there are numerous fundamental and technological questions yet to be addressed covering various aspects of this system for its commercialization, this study has employed first-principles DFT to model the [PbI6(CH3NH3)n]m zero-dimensional nanoclusters. Using the calculated binding energy landscapes, it has answered the question: why the corner-sharing PbI6 octahedron is surrounded by eight units of the organic cation in the large-scale supramolecular structures of the C…
Organic-inorganic hybrid perovskite architecture could serve as a robust platform for materials design to realize functionalities beyond photovoltaic applications. We explore caloric effects in organometal halide perovskites, taking methylammonium lead iodide (MAPbI$_3$) as an example, using all-atom molecular dynamics simulations with a first-principles based interatomic potential. The adiabatic thermal change is estimated directly by introducing different driving fields in the simulations. We find that MAPbI$_3$ exhibits both electrocaloric and mechanocaloric effects at room temperature. Loc…
Open circuit voltage decay measurements are performed on methylammonium lead iodide (CH3NH3PbI3) perovskite solar cells to investigate the charge carrier recombination dynamics. The measurements are compared to the two reference polymer-fullerene bulk heterojunction solar cells based on P3HT:PC60BM and PTB7:PC70BM blends. In the perovskite devices, two very different time domains of the voltage decay are found, with a first drop on a short time scale that is similar to the organic solar cells. However, two major differences are also observed. 65-70% of the maximum photovoltage persists on much…
We perform a thorough structural search with the minima hopping method (MHM) to explore low-energy structures of methylammonium lead iodide. By combining the MHM with a forcefield, we efficiently screen vast portions of the configurational space with large simulation cells containing up to 96 atoms. Our search reveals two structures of methylammonium iodide perovskite (MAPI) that are substantially lower in energy than the well-studied experimentally observed low-temperature $Pnma$ orthorhombic phase according to density functional calculations. Both structures have not yet been reported in the…
For opto-electronic and photo-voltaic applications of perovskites, it is essential to know the optical properties and intrinsic losses of the used materials. A systematic microscopic analysis is presented for the example of methylammonium lead iodide where density functional theory is used to calculate the electronic band structure as well as the dipole and Coulomb matrix elements. These results serve as input for a many-body quantum approach used to compute the absorption, photoluminescence, and the optical and Auger losses for a wide range of application conditions. To illustrate the theory,…
The defect tolerance nature of organic-inorganic hybrid perovskite is reflected from its stupendous growth in photovoltaic performances. The presence of lattice defect can manipulate or even gives rise to some exceptional properties which otherwise would have remained unseen. One of such properties reported in this article is the experimental observation of defect mediated room temperature ferromagnetism in methylammonium lead halide perovskite for the very first time, ably supported by ab-initio calculations. Theoretical analysis predicts the ferromagnetism principally arises from the iodide …
Excellent conversion efficiencies of over 20 % and facile cell production have placed hybrid perovskites at the forefront of novel solar cell materials with CH3NH3PbI3 being its archetypal compound. The question why CH3NH3PbI3 has such extraordinary characteristics, particularly a hugely efficient light absorption, is hotly debated with ferroelectricity being a promising candidate. This does, however, afford the crystal structure to be non-centrosymmetric and we herein present crystallographic evidence as to how the symmetry breaking occurs on a crystallographic, and therefore long-scale, leve…
Hybrid organic-inorganic perovskites have been established as good candidate materials for emerging photovoltaics, with device efficiencies of over 22 % being reported. There are currently only two organic cations, methylammonium and formamidinium, which produce 3D perovskites with band gaps suitable for photovoltaic devices. Numerous computational studies have identified azetidinium as a potential third cation for synthesizing organic-inorganic perovskites, but to date no experimental reports of azetidinium containing perovskites have been published. Here we prepare azetidinium lead iodide fo…
Organic-inorganic hybrid perovskites such as methylammonium lead iodide (CH3NH3PbI3) are game-changing semiconductors for solar cells and light-emitting devices owing to their exceptionally long carrier lifetime and diffusion length. Determining whether the large dipole moment of the organic cation and dynamic disorder benefit the optoelectronic properties of CH3NH3PbI3 has been an outstanding challenge. Herein, via transient absorption measurements employing an infrared pump pulse tuned to a methylammonium vibration, we observe slow, nanosecond-long thermal dissipation from the selectively ex…
In this paper we provide an accurate high-pressure structural and optical study of MAPbI3 hybrid perovskite. Structural data show the presence of a phase transition towards an orthorhombic structure around 0.3 GPa followed by full amorphization of the system above 3 GPa. After releasing pressure the systems keeps the high-pressure orthorhombic phase. The occurrence of these structural transitions is further confirmed by pressure induced variations of the photoluminescence signal at high pressure. These variations clearly indicate that the bandgap value and the electronic structure of MAPI chan…
We have accurately determined the exciton binding energy and reduced mass of single crystals of methylammonium lead tri-iodide using magneto-reflectivity at very high magnetic fields. The single crystal has excellent optical properties with a narrow line width of $\sim 3$meV for the excitonic transitions and a 2s transition which is clearly visible even at zero magnetic field. The exciton binding energy of $16 \pm 2$meV in the low temperature orthorhombic phase is almost identical to the value found in polycrystalline samples, crucially ruling out any possibility that the exciton binding energ…
The resilience to deep traps and localized defect formation is one of the important aspects that qualify a material as suited photo-absorber in solar cell devices. Here we investigate by ab-initio calculations the fundamental physics and chemistry of a number of possible localized defects in hybrid methylammonium lead-iodide perovskites. Our analysis encompasses a number of possible molecular fragments deriving from the dissociation of methylammonium. In particular, we found that in stoichiometric conditions both ammonia and methylamine molecules present lone-pair localized levels well within …
Mechanical strain can modify the structural and electronic properties of methylammonium lead iodide MAPbI3. The consequences of ferroelastic hysteresis, which involves the retention of structural memory upon cycles of deformation, in polycrystalline thin films of MAPbI3 are reported. Repeatedly bent films of MAPbI3 on flexible polyimide substrates were examined using Grazing Incidence Wide-Angle X-ray Scattering (GIWAXS) to quantitatively characterize the strain state, populations, and minimum sizes of twin domains. Approximate locations for the coercive stress and saturation on the ferroelast…
The most studied perovskite-based solar cells reported up to date contain the toxic lead in its composition. Photovoltaic research and development towards non-toxic, lead-free perovskite solar cells are critical to finding alternatives to reduce human health concerns associated with them. Bismuth-based perovskite variants, especially in the form of methylammonium bismuth iodide (MBI), is a good candidate for the non-toxic light absorber. However, the reported perovskite variant MBI thin flms prepared by the solution process so far suffers from poor morphology and surface coverage. In this work…
Organic-inorganic halide perovskites have been intensively re-investigated due to their applications, yet the opto-electronic function of the organic cation remains unclear. Through organic-selective resonant Auger electron spectroscopy measurements on well-defined single crystal surfaces, we find evidence for electronic coupling in the unoccupied states between the organic and inorganic sub-lattices of the prototypical hybrid perovskite, which is contrary to the notion based on previous studies that the organic cation is electronically inert. The coupling is relevant for electron dynamics in …
Transient opto-electrical measurements of methylammonium lead iodide (MALI) perovskite solar cells (PSCs) are performed and analyzed in order to elucidate the operating mechanisms. The current response to a light pulse or voltage pulse shows an extraordinarily broad dynamic range covering 9 orders of magnitude in time - from microseconds to minutes - until steady-state is reached. Evidence of a slowly changing charge density at the perovskite layer boundaries is found, which is most probably caused by mobile ions. Current-voltage curves (IV curves) are measured with very fast scan-rate after k…
Lead halide perovskites such as methylammonium lead triiodide (MAPI) have outstanding optical and electronic properties for photovoltaic applications, yet a full understanding of how this solution processable material works so well is currently missing. Previous research has revealed that MAPI possesses multiple forms of static disorder regardless of preparation method, which is surprising in light of its excellent performance. Using high energy resolution inelastic X-ray (HERIX) scattering, we measure phonon dispersions in MAPI and find direct evidence for another form of disorder in single c…
Hybrid organic-inorganic perovskites (HOIPs) have become an important class of semiconductors for solar cells and other optoelectronic applications. Electron-phonon coupling plays a critical role in all optoelectronic devices, and although the lattice dynamics and phonon frequencies of HOIPs have been well studied, little attention has been given to phonon lifetimes. We report the first high-precision measurements of acoustic phonon lifetimes in the hybrid perovskite methylammonium lead iodide (MAPI), using inelastic neutron spectroscopy to provide high energy resolution and fully deuterated s…
The hybrid halide perovskite CH3NH3PbI3 exhibits a complex structural behaviour, with successive transitions between orthorhombic, tetragonal and cubic polymorphs at ca. 165 K and 327 K. Herein we report first-principles lattice dynamics (phonon spectrum) for each phase of CH3NH3PbI3. The equilibrium structures compare well to solutions of temperature-dependent powder neutron diffraction. By following the normal modes we calculate infrared and Raman intensities of the vibrations, and compare them to the measurement of a single crystal where the Raman laser is controlled to avoid degradation of…
Origin of the Temperature-Induced Gap Bowing of Formamidinium-Methylammonium Lead Iodide Perovskites: Role of Cationic Rattlers
Institut de Ciència de Materials de Barcelona, ICMAB-CSIC（巴塞罗那材料科学研究所）；University of Bath（巴斯大学）；University of Bristol（布里斯托大学）；Cardiff University（卡迪夫大学）；ICREA（加泰罗尼亚高级研究院）
Environmental effects and intrinsic energy-loss processes lead to fluctuations in the operational temperature of solar cells, which can profoundly influence their power conversion efficiency. Here we determine from first principles the effects of temperature on the band gap and band edges of the hybrid pervoskite CH$_3$NH$_3$PbI$_3$ by accounting for electron-phonon coupling and thermal expansion. From $290$ to $380$ K, the computed band gap change of $40$ meV coincides with the experimental change of $30$-$40$ meV. The calculation of electron-phonon coupling in CH$_3$NH$_3$PbI$_3$ is particul…
Hybrid perovskites with mixed organic cations such as methylammonium and formamidinium have attracted interest due to their improved stability and capability to tune their properties varying the composition. In this work we report on the local variation of the structural and electronic properties in mixed A-site cation MA/FA lead iodide perovskites FAXMA1-XPBI3 evaluated from static first-principles calculations in certain structures where the orientations of organic cations result from examining the energy landscape of some compositions. The cation replacement at the A-site to form the solid …
We report the synthesis and crystal structure of an organic inorganic compound, ethylenediammonium lead iodide, NH3CH2CH2NH3PbI4. Synchrotron based single crystal X-ray diffraction experiments revealed that the pristine and thermally treated crystals differ in the organic cation behaviour, which is characterized by a partial disorder in the thermally treated crystal. Based on current voltage measurements, increased disorder of the organic cation is associated with enhanced photoconductivity. This compound could be a potential candidate for interface engineering in lead halide perovskite-based …
The crystal structure of the MAPbI$_3$ hybrid perovskite forms an intricate electrostatic puzzle with different ordering patterns of the MA molecules at elevated temperatures. For this perovskite three published model Hamiltonians based on the point-dipole (pd) approximation combined with short-range effective interactions are compared to a recently developed machine-learning force field. A molecular order parameter is used to consistently compare the transformation of the anti-ferroelectric ordering in the orthorhombic phase upon raising the temperature. We show that the ground states and the…
Using density functional theory calculations, we have investigated the interlayer cation exchange phenomena in muscovite mica, which is motivated by a necessity to develop flexible high-insulating covering materials. The crystalline structures, chemical bonding properties, energetics, and electronic properties of muscovites before and after exchange of interlayer K$^+$ cation with ammonium (NH$_4^+$) or methylammonium (CH$_3$NH$_3^+$) ion were calculated. It was found that the unit cell volume changes are negligibly small upon exchange with NH$_4^+$ ion, while the unit cells are expanded with …
Organic-inorganic hybrid halide perovskites, in which the A cations of an ABX$_3$ perovskite are replaced by organic cations, may be used for photovoltaic and solar thermoelectric applications. In this contribution, we systematically study three lead-free hybrid perovskites, i.e., methylammonium tin iodide CH$_3$NH$_3$SnI$_3$, ammonium tin iodide NH$_4$SnI$_3$, and formamidnium tin iodide HC(NH$_2$)$_2$SnI$_3$, by first-principles calculations. We find that in addition to the commonly known motif in which the corner-shared SnI$_6$ octahedra form a three-dimensional network, these materials may…
Methylammonium lead iodide perovskites are considered direct bandgap semiconductors. Here we show that in fact they present a weakly indirect bandgap 60 meV below the direct bandgap transition. This is a consequence of spin-orbit coupling resulting in Rashba-splitting of the conduction band. The indirect nature of the bandgap explains the apparent contradiction of strong absorption and long charge carrier lifetime. Under hydrostatic pressure from ambient to 325 MPa, Rashba splitting is reduced due to a pressure induced ordering of the crystal structure. The nature of the bandgap becomes increa…
Single-atom catalysts (SACs) combine the best of two worlds by bridging heterogeneous and homogeneous catalysis. The superior catalytic properties of SACs, however, can hardly be exploited without a suitable substrate. Here, we explore the possibility of using hybrid organic-inorganic perovskites as supporting materials for single transition-metal atoms. By means of first-principles calculations, we predict that single Pt atoms can be incorporated into methylammonium lead iodide surfaces by replacing the methylammonium groups at the outermost layer. The iodide anions at the surface provide pot…
Methylammonium lead iodide perovskite has attracted intensive interest for its diverse optoelectronic applications. However, most studies to date have been limited to bulk thin films that are difficult to implement for integrated device arrays because of their incompatibility with typical lithography processes. We report the first patterned growth of regular arrays of perovskite microplate crystals for functional electronics and optoelectronics. We show that large arrays of lead iodide microplates can be grown from an aqueous solution through a seeded growth process and can be further intercal…
Despite the widespread use of solution-processable hybrid organic-inorganic perovskites in photovoltaic and light-emitting applications, determination of their intrinsic charge transport parameters has been elusive due to the variability of film preparation and history-dependent device performance. Here we show that screening effects associated to ionic transport can be effectively eliminated by lowering the operating temperature of methylammonium lead iodide perovskite (CH3NH3PbI3) field-effect transistors (FETs). Field-effect carrier mobility is found to increase by almost two orders of magn…
This study introduces a new chemical method for controlling the strain in methylammonium lead iodide (MAPbI3) perovskite crystals by varying the ratio of Pb(Ac)2 and PbCl2 in the precursor solution. To observe the effect on crystal strain, a combination of piezoresponse force microscopy (PFM) and X-ray diffraction (XRD) is used. The PFM images show an increase in the average size of ferroelastic twin domains upon increasing the PbCl2 content, indicating an increase in crystal strain. The XRD spectra support this observation with strong crystal twinning features that appear in the spectra. This…
The esoteric importance of intermolecular hydrogen bonding interaction to design novel methylammonium trihalide organic-inorganic hybrid perovskite solar cell materials is uncovered, establishing the unified structure-property relationship between the calculated Y...H intermolecular hydrogen bonding distance and the experimentally reported onset of optical absorption (bandgap) for the bulk geometries of the ten-membered methylammonium lead trihalide (CH3NH3PbY3) perovskite solar cell series, where Y = X (X = Cl, Br, I) and the mixed halogen derivatives. The same relationship is also revealed f…
Recently, an aziridinium lead iodide perovskite was proposed as a possible solar cell absorber material. We investigated the stability of this material using a density-functional theory with an emphasis on the ring strain associated with the three-membered aziridinium cation. It is shown that the aziridinium ring is prone to opening within the PbI$_3$ environment. When exposed to moisture, aziridinium lead iodide can readily react with water. The resultant product will not likely be a stoichiometric lead halide perovskite structure.
We present Raman and terahertz absorbance spectra of methylammonium lead halide single crystals (MAPbX3, X = I, Br, Cl) at temperatures between 80 and 370 K. These results show good agreement with density-functional-theory phonon calculations.1 Comparison of experimental spectra and calculated vibrational modes enables confident assignment of most of the vibrational features between 50 and 3500 cm-1. Reorientation of the methylammonium cations, unlocked in their cavities at the orthorhombic-to-tetragonal phase transition, plays a key role in shaping the vibrational spectra of the different com…
The long charge carrier lifetime of the hybrid organic-inorganic perovskites (HOIPs) is the key for their remarkable performance as a solar cell material. The microscopic mechanism for the long lifetime is still in debate. Here, by using muon spin relaxation technique that probes the fluctuation of local magnetic fields, we show that the muon depolarization rate ($Δ$) of a prototype HOIP methylammonium lead iodide (MAPbI$_3$) shows a sharp decrease with increasing temperature in two steps above 120 K and 190 K across the structural transition from orthorhombic to tetragonal structure at 162 K.…
In this work, we use density functional theory calculations to demonstrate how spontaneous electric polarizations can be induced \textit{via} a hybrid improper ferroelectric mechanism in iodide perovskites, a family well-known to display solar-optimal band gaps, to create new materials for photoferroic applications. We first assemble three chemically distinct ($A$$A^{\prime}$)($B$$B^{\prime}$)I$_6$ double perovskites using centrosymmetric $AB$I$_3$ perovskite iodides (where $A$ = Cs, Rb, K and $B$ = Sn, Ge) as building units. In each superlattice, we investigate the effects of three types of $…
The low ionization energy of an $A$ site molecule is a very important factor, which determines the thermodynamical stability of $A$PbI$_3$ hybrid halide perovskites, while the size of the molecule governs the stable phase at room temperature and, eventually, the bandgap. It is challenging to achieve both a low ionization energy and the reasonable size for the PbI$_3$ cage to circumvent the stability issue inherent to hybrid halide perovskites. Here we propose a new three-membered charged ring radical, which demonstrates a low ionization energy that renders a good stability for its correspondin…
Despite the imperative importance in solar-cell efficiency, the intriguing phenomena at the interface between perovskite solar-cell and adjacent carrier transfer layers are hardly uncovered. Here we show that PbI$_2$/AI-terminated lead-iodide-perovskite (APbI$_3$; A=Cs$^+$/ methylammonium(MA)) interfaced with the charge transport medium of graphene or TiO2 exhibits the sizable/robust Rashba-Dresselhaus (RD) effect using density-functional-theory and ab initio molecular dynamics (AIMD) simulations above cubic-phase temperature. At the PbI$_2$-terminated graphene/CsPbI3(001) interface, ferroelec…
Organic-inorganic hybrid perovskites (OIHPs) exhibiting exceptional photovoltaic and optoelectronic properties are of fundamental and practical interest, owing to their tunability and low manufacturing cost. For practical applications, however, challenges such as material instability and the photocurrent hysteresis occurring in perovskite solar cells under light exposure need to be understood and addressed. While extensive investigations have suggested that ion migration is a plausible origin of these detrimental effects, detailed understanding of the ion migration pathways remains elusive. He…
The family of organic-inorganic tri-halide perovskites including MA (MethylAmmonium)PbI$_{3}$, MAPbI$_{3-x}$Cl$_{x}$, FA (FormAmidinium)PbI$_{3}$ and FAPbBr$_{3}$ are having a tremendous impact on the field of photovoltaic cells due to their ease of deposition and efficiencies, but device performance can be significanly affected by inhomogeneities. Here we report a study of temperature dependent micro-photoluminescence which shows a strong spatial inhomogeneity related to the presence of microcrystalline grains, which can be both light and dark. In all of the tri-iodide based materials there i…
Single crystals of the methylammonium (MA) lead halides MAPbI3, MAPbBr3, and MAPbCl3 have been investigated using infrared spectroscopy with the aim of analyzing structural and dynamical aspects of processes that enable the ordering of the MA molecule in the orthorhombic crystal structure of these hybrid perovskites. Our temperature-dependent studies were focused on the analysis of the CH/NH rocking, C-N stretching, and CH/NH bending modes of the MA molecule in the 800-1750 cm-1 frequency range. They deliver a direct comparison of the behavior of the three halides on crossing the orthorhombic-…
We have observed short-lived optical birefringence in a CH$_3$NH$_3$PbBr$_3$ single crystal induced by a powerful nearly single-cycle terahertz pulse. Apart from the instantaneous contribution that follows the profile of the squared pump electric field, the recorded anisotropy signal contains an exponential component decaying in $\sim$ 350 fs, underdamped oscillations at the frequency of $\sim$ 0.16 THz and an intermediate picosecond relaxation process with a Gaussian tail. We associate these three non-trivial features with, respectively, Kerr effect in the inorganic lattice, terahertz-induced…
Owing to their exceptional semiconducting properties, hybrid inorganic-organic perovskites show great promise as photovoltaic absorbers. In these materials, long-range diffusion of charge carriers allows for most of the photogenerated carriers to contribute to the photovoltaic efficiency. Here, time-resolved photoluminescence (PL) microscopy is used to directly probe ambipolar carrier diffusion and recombination kinetics in hybrid perovskites. This technique is applied to thin films of methylammonium lead tri-iodide MAPbI$_3$ obtained with two different fabrication routes, methylammonium lead …
By means of non-resonant Raman spectroscopy and density functional theory calculations, we measure and assign the vibrational spectrum of two distinct two-dimensional lead-iodide perovskite derivatives. These two samples are selected in order to probe the effects of the organic cation on lattice dynamics. One templating cation is composed of a phenyl-substituted ammonium derivative, while the other contains a linear alkyl group. We find that modes that directly involve the organic cation are more prevalent in the phenyl-substituted derivative. Comparison of the temperature dependence of the Ra…
2D organic-inorganic hybrid perovskites (2DHPs) consist of alternating anionic metal-halide and cationic organic layers. They have widely tunable structural and optical properties. We review the role of the organic cation in defining the structural and optical properties of 2DHPs through example lead iodide 2DHPs. Even though excitons reside in the metal halide layers, the organic and inorganic frameworks cannot be separated-they must be considered as a single unit to fully understand the photophysics of 2DHPs. We correlate cation-induced distortion and disorder in the inorganic lattice with t…
We have developed a multi-scale model for organic-inorganic hybrid perovskites (HPs) that applies quantum mechanical (QM) calculations of small HP supercell models to large coarse-grained structures. With a mixed quantum-classical hopping model, we have studied the effects of cation disorder on charge mobilities in HPs, which is a key feature to optimize their photovoltaic performance. Our multi-scale model parametrizes the interaction between neighboring methylammonium cations (MA$^+$) in the prototypical HP material, methylammonium lead triiodide (CH$_3$NH$_3$PbI$_3$, or MAPbI$_3$). For the …
Organic or inorganic (A) metal (M) halide (X) perovskites (AMX3) are semiconductor materials setting the basis for the development of highly efficient, low-cost and multijunction solar energy conversion devices. The best efficiencies nowadays are obtained with mixed compositions containing methylammonium, formamidinium, Cs and Rb as well as iodine, bromine and chlorine as anions. The understanding of fundamental properties such as crystal structure and its effect on the band gap, as well as their phase stability is essential. In this systematic study X-ray diffraction and photoluminescense spe…
The chemical stability of methylammonium lead iodide (\ce{MAPbI3}) under humid conditions remains the primary challenge facing halide perovskite solar cells. We investigate defect processes in the water-intercalated iodide perovskite (\ce{MAPbI3}\_\ce{H2O}) and monohydrated phase (\ce{MAPbI3}$\cdot$\ce{H2O}) within a first-principles thermodynamic framework. We consider the formation energies of isolated and aggregated vacancy defects with different charge states under I-rich and I-poor conditions. It is found that a \ce{PbI2} (partial Schottky) vacancy complex can be formed readily, while the…
