Methylammonium Lead Iodide CH3NH3PbI3 Research Articles

Theoretical spectral function of CH3NH3PbI3 hybrid perovskite around the Fermi level

Methylammonium lead iodide CH3NH3PbI3 (MAPI) is one of the hybrid organic–inorganic perovskites (HOIPs) widely considered for photovoltaic devices. Since photoemission is possibly the best technique for the experimental determination of the bands, we have calculated photoemission spectra at the main photon energies available at conventional laboratories (He I - 21.2 eV, He II - 40.8 eV) by performing fully relativistic Spin-Polarized Relativistic Korringa–Kohn–Rostoker (SPRKKR) calculations. Similarly, we have studied how s- and p-polarization affect to the calculated spectra. These studies could help to reach a better understanding of photoemission measurements on MAPI.

New Insights into Interfacial Passivation on 3D Graphene–CuInS2 Composites‐Based Perovskite Solar Cells

Although it is generally accepted by the perovskite solar cells community that their interface behaviors have a profound impact on their power conversion efficiency (PCE) and stability, such interfacial engineering on the bottom interface between electron transport layer (ETL) and perovskite film is still lagging. Herein, a 3D graphene (G)–CuInS2 composite is designed as an efficient ETL to improve both the interfacial contact and passivate defects at the G–CuInS2/perovskite interface. The lattice matching of graphene and methylammonium lead iodide CH3NH3PbI3 inhibits the concentrated stress generated during the growth of perovskite, resulting in crystal films with large grain boundaries. The low‐electron defect density in 3D G–CuInS2 composite facilitates the electron transport from perovskite film to CuInS2 quantum dots. In addition, 3D G–CuInS2 shows excellent carrier extraction capability of reducing carrier extraction time by 1.47 times than that of the counterpart. Correspondingly, a highly improved PCE of 22.4% is obtained, which increases by 15% of the counterpart. Furthermore, the unencapsulated device based on 3D G–CuInS2 shows long‐term stability, maintaining 85% of its original efficiency in air for 30 days. This strategy provides a new route to interfacial passivation engineering for preparation of high‐performance perovskite solar cells.

Guidelines for the Design of High-Performance Perovskite Based Solar Cells

In the aim of finding the optimal solar cell structure which allows better efficiency, stability and reduced cost, a general study of a Methyl Ammonium lead Iodide CH3NH3PbI3 based perovskite solar cell is made. Three different electron transport material compounds ETMs; TiO2, ZnO and SnO2 are comparatively studied considering the same hole transport material HTM, Spiro-OMeTAD. The photovoltaic parameters, i.e. the open circuit voltage (Voc), the short circuit current (Jsc) and the power conversion efficiency (PCE) are performed considering the ETM layers thicknesses, and the defect densities in both interfaces ETM/Perovskite and Perovskite/HTM. It is found that solar cell with SnO2 present the highest PCE for almost all configurations. Finally, the optimized cell is simulated with different organic and inorganic HTMs such as PEDOT: PSS, Cul and CuSbS2.

The Effect of Ethanol Solvent on Characterization of MAPbI<sub>3</sub> Perovskite

Methyl ammonium lead iodide CH3NH3PbI3 Perovskite was synthesized by a new method mixing between one and two steps, in addition, the ethanol solvent was used to dissolve CH3NH3I and compared with isopropanol solvent. The characterizations of synthesized perovskite samples included the structural properties, morphological characteristics and optical properties. The intensity and orientation in X-ray diffraction patterns appear clearly in ethanol solvent while disappearing at a peak at 12o due to the speed reaction of perovskite in this solvent. Additionally, the ethanol solvent increasing the grain size of perovskite which homogeneity of the surface morphology. the ethanol solvent cause a decrease in the wavelength of absorbance edge in addition to an increase in the energy bandgap value. Keywords: Ethanol Solvent, Perovskite, Photovoltaic Technologies, X-ray diffraction.

Electronic structures, spectroscopic properties, and thermodynamic characterization of sodium- or potassium-incorporated CH3NH3PbI3 by first-principles calculation

Influence of alkali metals such as sodium (Na) and potassium (K) in methyl ammonium lead iodide CH3NH3PbI3 perovskite crystal on electronic structures, spectroscopic properties, and thermodynamic properties was investigated by first-principles calculation. Partial substitution of CH3NH3 with Na or K in the perovskite crystal generated 3s, 3p, 4s, and 4p orbitals of Na or K above conduction band, which promoted the charge transfer from the alkali metals to the conduction band, accelerating the carrier generation and diffusion related to the photovoltaic performances. The molar absorption coefficient and oscillation strength were increased by a slight deviation of the charge distribution near ligand in the coordination structure. The splitting of chemical shift of 127I-NMR in magnetic field was caused by a slight perturbation of the coordination structure with nuclear quadrupole interaction based on electronic field gradient. Decrease of the Gibbs free energy and entropy indicated the thermodynamic stabilization without scattering carrier diffusion as phonon effectiveness. The decrease of the entropy was based on a slight change of stretching vibration mode of Pb–I bond with vending mode of N–H and C–H bonds in the infrared and Raman spectra. The minor addition of 12.5% Na or K into the perovskite crystal will improve the photovoltaic properties, open voltage related to band gap, and short-circuit current density based on the carrier diffusion with phonon effectiveness.

Optoelectronic and morphology properties of perovskite/silicon interface layer for tandem solar cell application

Silicon (Si) solar cell has low optical absorption because of the low and indirect bandgap of Si, and the efficiency was trapped at 25% for 15 years. Si solar cell is able to achieve efficiency up to 30% by adding perovskite as multiple bandgap material through tandem formation. In this paper, the Si/perovskite interface layer was characterized to study the compatibility of perovskite on fluorine‐doped tin oxide (FTO) glass and p‐type Si wafer (p‐Si). The single solution deposition step of methyl ammonium lead iodide, CH3NH3PbI3(MAPbI3) perovskite film, was spin‐coated at different concentration. The physical properties of the MAPbI3/FTO and MAPbI3/p‐Si were obtained by profilometer, atomic force microscope, X‐ray diffraction, and Raman spectroscopy. The optical properties were analyzed by ultraviolet‐visible spectroscopy, photoluminescence, and infrared transmission. Then the electrical properties were measured by Hall effect. From the measurement, it is observed that 1.2M concentration of MAPbI3thin film has the highest thickness, smoothest film surface, and largest crystallite size compared with 0.8M and 1.0M. It is found that there is an interaction in perovskite/Si interface and caused in a low‐wavelength shift, and the increase in concentration of MAPbI3helped in intensifying the Raman signal produced. 1.2M MAPbI3thin film had the highest enhancement in light trapping property rather than 0.8M and 1.0M. The bulk concentration and conductivity of 1.2M perovskite were higher, but the resistivity was lower than 0.8M MAPbI3because of more CH3NH3I and PbI2concentration within MAPbI3perovskite compound.

Rapid Characterization and Parameter Space Exploration of Perovskites Using an Automated Routine.

Hybrid, e.g., organic inorganic, perovskites from the type methylammonium lead iodide CH3NH3PbI3 are promising solar cell materials. However, due to the large parameter space spanned by the manifold combinations of divalent metals with organic cations and anions, an efficient approach is needed to rapidly test and categorize new promising materials. Herein, we developed a high throughput approach for the automated synthesis of perovskite layers with different precursor ratios at varying annealing temperatures. The layers were analyzed by optical absorption and photoluminescence (PL) spectroscopy as well as X-ray diffraction (XRD) and evaluated using two different procedures. The first one is a stepwise exclusion of nonperforming reactant ratios and synthesis conditions by using both spectroscopic techniques, followed by a final validation of the procedure by XRD. In the second procedure, only PL results were consulted in combination with high throughput screening using design of experiments (DoE) to reduce the total number of experiments needed and compared to the manual cascade approach. Noteworthy, by simple PL screening, it was possible to identify the best ratio of perovskite to byproducts and annealing temperature. Thus, only with PL, more detailed results as with the manual protocol were reached, while at the same time the effort for characterization was significantly reduced (by 60% of the experimental time). In conclusion, our approach opens a way toward fast and efficient identification of new promising materials under different reaction and process conditions.

Thermodynamic Stability and Structural Insights for CH3NH3Pb1\u2212xSixI3, CH3NH3Pb1\u2212xGexI3, and CH3NH3Pb1\u2212xSnxI3 Hybrid Perovskite Alloys: A Statistical Approach from First Principles Calculations

The recent reaching of 20% of conversion efficiency by solar cells based on metal hybrid perovskites (MHP), e.g., the methylammonium (MA) lead iodide, CH3NH3PbI3 (MAPbI3), has excited the scientific community devoted to the photovoltaic materials. However, the toxicity of Pb is a hindrance for large scale commercial of MHP and motivates the search of another congener eco-friendly metal. Here, we employed first-principles calculations via density functional theory combined with the generalized quasichemical approximation to investigate the structural, thermodynamic, and ordering properties of MAPb1−xSixI3, MAPb1−xGexI3, and MAPb1−xSnxI3 alloys as pseudo-cubic structures. The inclusion of a smaller second metal, as Si and Ge, strongly affects the structural properties, reducing the cavity volume occupied by the organic cation and limitating the free orientation under high temperature effects. Unstable and metaestable phases are observed at room temperature for MAPb1−xSixI3, whereas MAPb1−xGexI3 is energetically favored for Pb-rich in ordered phases even at very low temperatures. Conversely, the high miscibility of Pb and Sn into MAPb1−xSnxI3 yields an alloy energetically favored as a pseudo-cubic random alloy with tunable properties at room temperature.

Temperature dependence of the effective mass of the hybrid organic-inorganic perovskites CH3NH3PbI3

The material of methylammonium lead iodide, CH3NH3PbI3 (MAPbI3), has shown significant promise in solar cell applications. A way to infer the microscopic scattering mechanism(s) in MAPbI3 is through the measured temperature dependence of carrier mobility. To this end, how does the carrier effective mass depend on temperature, m* = m*(T), is a useful information since the mobility is a function of m*. By atomistic first principles, we report the calculated m*(T) due to the thermal expansion of MAPbI3 materials, in the experimentally relevant range of 130 K to room temperature. The calculated results suggest m* = m*(T) to be linear in T. The increase of m* versus temperature is predominantly due to the expansion of the longitudinal atomic spacing that weakens the s/p hybridization between the I/Pb atoms.

Influence of processing temperature and precursor composition on phase region of solution processed methylammonium lead iodide perovskite

Solution processed organic–inorganic metal halide perovskite and its derivatives are promising in the development of efficient thin film photovoltaic devices. In the context of increasing the efficiency and sustainability of perovskite solar cells (PSC) devices, we have attempted to experimentally develop phase diagram for solution processed methyl ammonium lead iodide (CH3NH3PbI3 (MAPbI3)) perovskite. The phase diagram emphasized the role of processing parameters (precursor composition and crystallization temperature) on the crystallographic functionality and optical band gap of perovskite. The phase dynamics of low dimensional perovskite, which has emerged as a potential candidate for absorber layer in perovskite solar cells (PSC) with higher stability in ambient conditions is also discussed. We observed that crystallization via non-equilibrium annealing introduced lattice strain in perovskite which affected the crystallographic properties of perovskite. A highly crystalline perovskite, with large grain size was obtained by optimizing the crystallization parameters and precursor composition together with nucleation of perovskite crystal and its growth dynamics.

Unravelling the low-temperature metastable state in perovskite solar cells by noise spectroscopy.

The hybrid perovskite methylammonium lead iodide CH3NH3PbI3 recently revealed its potential for the manufacturing of low-cost and efficient photovoltaic cells. However, many questions remain unanswered regarding the physics of the charge carrier conduction. In this respect, it is known that two structural phase transitions, occurring at temperatures near 160 and 310 K, could profoundly change the electronic properties of the photovoltaic material, but, up to now, a clear experimental evidence has not been reported. In order to shed light on this topic, the low-temperature phase transition of perovskite solar cells has been thoroughly investigated by using electric noise spectroscopy. Here it is shown that the dynamics of fluctuations detect the existence of a metastable state in a crossover region between the room-temperature tetragonal and the low-temperature orthorhombic phases of the perovskite compound. Besides the presence of a noise peak at this transition, a saturation of the fluctuation amplitudes is observed induced by the external DC current or, equivalently, by light exposure. This noise saturation effect is independent on temperature, and may represent an important aspect to consider for a detailed explanation of the mechanisms of operation in perovskite solar cells.

Methylammonium Lead Iodide for Efficient X-ray Energy Conversion

We report on photocurrent generation by X-ray irradiation in methylammonium lead iodide CH3NH3PbI3 single crystals. We observed 75% of charge collection efficiency in millimeter sized samples. This efficiency is partially due to the high photon absorption coefficient and X-ray beam stopping power of our lead containing material. The material shows a less than 20% decrease in its performance up to 40 Sv of total X-ray dose, which represents a very good stability. Moreover, our Monte Carlo N-Particle Transport calculations indicate that energetic particle radiation can also be harvested by CH3NH3PbI3. These properties are compared to CH3NH3SnI3 and PbI2. The possible application of these advantageous properties could be in simultaneous radiation protection and direct electricity production in environments with highly energetic background radiation.

ELECTRODEPOSITION OF ZnO NANOROD ARRAYS FOR APPLICATION IN PEROVSKITE BASED SOLAR CELLS

We report a low-cost, free-hole conductor methylammonium lead iodide CH3NH3PbI3 (perovskite)/ZnO nanorods (NR) heterojunction solar cell. ZnO nanorod arrays were obtained electrochemically onto transparent conducting oxide (fluor doped tin oxide, FTO) from an aqueous solution of zinc acetate. The ZnO NR were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and optical transmittance. Solar cell was fabricated forming the perovskite material onto the ZnO thin film. Spin coating of an equimolar mixture of CH3NH3I and PbI2 in γ-butyrolactone solution (perovskite precursor solution) leads to CH3NH3PbI3 formation on ZnO NR. A graphite-covered FTO/glass was used as a back contact. The photovoltaic performance of the solar cell was characterized at full sun intensity of 100 mW/cm2 obtaining a shortcircuit current of 1.5 mA/cm2, an open circuit voltage of 0.47 V and energy conversion efficiency of 0.16 %.

Mechanical Origin of the Structural Phase Transition in Methylammonium Lead Iodide CH3NH3PbI3.

The methylammonium lead iodide perovskite (MAPbI3) is presently a desirable material for photovoltaic application. Its structure is orthorhombic at low temperature and tetragonal at room temperature. Most theoretical works have focused on either tetragonal or orthorhombic phase alone leaving a gap in the understanding of the structural phase transition in between. In this work, by ab initio calculations, we elucidate the origin of structural phase transition between these two phases. We show that there exists a critical ratio of out-of-plane to in-plane lattice constants, c/a ∼ 1.45, where at low c/a the orthorhombic Pnma phase is stable while the tetragonal I4/mcm phase is stable at high c/a. Varying the c/a ratio leads to a change of PbI6 octahedral tilting with the rotation of CH3NH3(+) cations about the NH3 component in and out of the Oxy plane. The origin of this rotation is identified. We propose that under epitaxial conditions a gradual change in structural phase of the MAPbI3 perovskite may exist and understanding its electronic properties will be beneficial toward the solar cell community.