The electronic properties of ABX3 type compounds in the cubic phase are systematically studied using the first-principles calculations. The chemical trend of their properties as A or B or X varies is fully investigated. The optical properties of the ABX3 compounds are also investigated. Our calculations show that taking into account the spin–orbit coupling effect is crucial for predicting the accurate band gap of these halide perovskites. We predict that CH3NH3SnBr3 is a promising material for solar cells absorber with a perfect band gap and good optical absorption. 相似文献
We analysed perovskite CH3NH3PbI3-xClx inverted planer structure solar cell with nickel oxide (NiO) and spiro-MeOTAD as hole conductors. This structure is free from electron transport layer. The thickness is optimized for NiO and spiro-MeOTAD hole conducting materials and the devices do not exhibit any significant variation for both hole transport materials. The back metal contact work function is varied for NiO hole conductor and observed that Ni and Co metals may be suitable back contacts for efficient carrier dynamics. The solar photovoltaic response showed a linear decrease in efficiency with increasing temperature. The electron affinity and band gap of transparent conducting oxide and NiO layers are varied to understand their impact on conduction and valence band offsets. A range of suitable band gap and electron affinity values are found essential for efficient device performance. 相似文献
Organohalide perovskite optoelectronics based upon large (mm‐sized) single crystals present exciting opportunities for new device platforms and fundamental studies. Herein, we report CH3NH3PbBr3 and CH3NH3PbI3 single crystals prepared via an inverse temperature crystallization method with strong near infrared photoresponses significantly below the optical gap. Light intensity dependent photocurrent measurements reveal the photoresponse is not a two‐photon phenomenon, but rather is derived from a linear mechanism. The effect (including responsivity and speed) is enhanced in a photoresistor architecture, indicating that the photoresponse is due to absorption into surface trap states in the crystal. Without any optimisation, respectable NIR responsivities at room temperature of ∼10‐2 A W−1 at a low 1V bias operating voltage are achieved. These results again demonstrate the remarkable potential of organohalide perovskites as light sensing materials, and the possibilities for engineering a new class of single crystal‐based optoelectronics.
Band gap modulation engineering is an important step in the application of optoelectronic materials. In this paper, the first-principles calculations were carried out to study the influence of strain, external electric field, spatial orientation of organic cation on the band gaps and electronic structures of organic-inorganic hybrid halide perovskites CH3NH3PbI3. The results show that both the uniform strain and the tetragonal deformation can modulate the band gap obviously. The electric field of 0.2 V/Å is the critical point of the band gap modulation. The band gap increases when an electric field is applied from 0 to 0.2 V/Å. The electric field above 0.2 V/Å will cause the band gap to decrease. The spatial orientation of the organic cation also has modulation influence on the band gap of CH3NH3PbI3, but has no effect on the direct semiconductor characteristics. The above results will be helpful to study the band gap modulation of other organic-inorganic hybrid halide perovskites. 相似文献
Organic-inorganic hybrid perovskite solar cells have excellent optoelectronic properties, but their low thermal and chemical stabilities limit their commercial applications. In this paper, a new type of organic-inorganic hybrid perovskite is proposed. Malondiamide (MA,CH2(CONH2)2) and propionamide (PA, CH3CH2CONH2) were used as organic layers, with Pb-I octahedral inorganic layers to form quasi three-dimensional (3D) perovskites. The crystal structure, stability, electronic structure, and optical properties of MAPbI4 and PAPbI4 perovskites were investigated, and the results showed that there were localized states that corresponded to the number of acyl groups in the two perovskites. Energy band calculations showed that the localized states of the two perovskites rose above the bottom of the conduction band. This can be used to regulate the band gap of the two perovskites, which affects the electronic properties and optical absorption characteristics of the two perovskites. Compared with PAPbI4, MAPbI4 has a lower formation energy, lower band gap, lower effective mass of electrons and holes, wider energy range, and larger absorption coefficient, which indicates that MAPbI4 is more suitable for use in solar cells. This study provides guidance for obtaining efficient and stable photovoltaic materials. 相似文献
The polycrystalline samples La0.67Ca0.33Mn(1?x)FexO3 (x?=?0.00,?0.01,?0.03, and 0.1) have been grown in single phase by solid state route. The analysis of the reaction has been done by thermogravimetry and differential thermal analysis measurements. DC electrical resistivity measurements have been carried out down to 15?K. The samples with x?=?0.00, 0.01, and 0.03 exhibit metal–insulator (MI) transition at temperatures 221.5?K, 217?K, and 215?K respectively, whereas the sample with x?=?0.1 is insulating in nature for entire temperature range. Interestingly, the electric transport properties of these samples are not consistent with their magnetic phase transitions and the samples show MI transition at a temperature, TMI, which is significantly lower than the paramagnetic to ferromagnetic transition temperature (Tc). The resistivity data below TMI has been analyzed using the empirical relation ρ?=?ρ0?+?ρ1Tn and the data above this temperature has been analyzed using two existing models, Mott's variable range hopping model and spin polaronic conduction model. 相似文献
The spin dipole–spin dipole and spin–orbit coupling contributions to the zero-field splitting parameters D and E of [CH3–N–CH3]+, [CH3–P–CH3]+, and [CH3–As–CH3]+ have been calculated from CASSCF(14,14)/cc-pVTZ wave functions and the Breit–Pauli Hamiltonian at T1 B3LYP/cc-pVTZ optimized geometries. The spin–orbit coupling contributions represent a minor correction for the dimethylnitrenium cation, which has a triplet ground state. They dominate the spin–spin terms by an order of magnitude in the dimethylphosphenium cation and by more than two orders of magnitude in the dimethylarsenium cation, both of which have a singlet ground state. The properties of all these biradicaloids follow expectations based on the simple algebraic 2-in-2 model of biradical structure. 相似文献
In this study, we built a perovskite solar cells(PSCs) model with a Au/CuSCN/CH3NH3Sn1−xPbxI3/TiO2/FTO glass structure using the SCAPS program and use polynomial fitting to obtain the relationship between the conduction/valence bands of CH3NH3Sn1−xPbxI3 and the x value, which is more complex and accurate than that in any previous research. The influences of thickness, electron and hole mobilities, relative permittivity, effective conduction band density, effective valence band density, and the value of x on the solar cell performance are analyzed. Furthermore, we simulate the situation where the doping concentration changes with the absorption layer depth of the device and a special bandgap is formed. The power conversion efficiency of the device improves from 19.96% to 20.52%, with an open-circuit voltage of 0.776 V, a short-circuit current of 33.79 mA/cm2, and a filling factor of 77.39% when double gradient doping is performed. The application value of gradient doping in the device absorption layer is obtained. 相似文献
The dielectric constant of (CH3NH3)2 CdCl4 has been measured as a function of temperature in the submillimeter range. Freshly grown samples with a wide domain structure at room temperature show a pronounced dichroism in this spectral range which is caused by the orientation of the molecules in the room temperature orthorhombic phase and their response to the electromagnetic wave. 相似文献
The spontaneous polarization influence on the refractive index of BaTiO3 and KNbO3 perovskites is analysed from their band structure. The coupling effects between the conduction band edge and the spontaneous polarization are expressed through the Bloch orbital interactions and allow to interpret the presence of a precursor polarization in the paraelectric phase and the refractive index experimental data. 相似文献
We use moving‐window two‐dimensional correlation spectroscopy (MW‐2DCOS) for phase‐specific Raman analysis of the n‐alkane (C21H44) during melting from the crystalline solid phase to the intermediate rotator phase and to the amorphous molten phase. In MW‐2DCOS, individual peak‐to‐peak correlation analysis within a small subset of spectra provides both temperature‐resolved and spectrally disentangled Raman assignments conducive to understanding phase‐specific molecular interactions and chain configurations. We demonstrate that autocorrelation MW‐2DCOS can determine the phase transition temperatures with a higher resolving power than commonly used analysis methods including individual peak intensity analysis or principal component analysis. Besides the enhanced temperature resolving power, we demonstrate that asynchronous 2DCOS near the orthorhombic‐to‐rotator transition temperature can spectrally resolve the two overlapping peaks embedded in the Raman CH2 twisting band in the orthorhombic phase, which had been only predicted but not observed because of thermal broadening near the melting temperature. Published 2016. This article is a U.S. Government work and is in the public domain in the USA. 相似文献