Optical Properties and First-Principles Study of CH3NH3PbBr3 Perovskite Structures

Al Ghaithi A, Qamhieh N, Amrane N, Benkraouda M, Liu S(F, Najar A. Towards High Performance: Solution-Processed Perovskite Solar Cells with Cu-Doped CH3NH3PbI3

Perovskite solar cells (PSCs) have demonstrated remarkable photovoltaic performance, positioning themselves as promising devices in the field. Theoretical calculations suggest that copper (Cu) can serve as an effective dopant, potentially occupying interstitial sites in the perovskite structure, thereby reducing the energy barrier and enhancing carrier extraction. Subsequent experimental investigations confirm that adding CuI as an additive to MAPbI3-based perovskite cells improves optoelectronic properties and overall device performance. Optimizing the amount of Cu (0.01 M) has been found to significantly enhance crystalline quality and grain size, leading to improved light absorption and suppressed carrier recombination. Consequently, the power conversion efficiency (PCE) of Cu-doped PSCs increased from 16.3% to 18.2%. However, excessive Cu doping (0.1 M) negatively impacts morphology, resulting in inferior optical properties and diminished device performance. Furthermore, Cu-doped PSCs exhibit higher stabilized power output (SPO) compared to pristine cells. This study underscores the substantial benefits of Cu doping for advancing the development of highly efficient PSCs.

Optoelectronic Properties Prediction of Lead-Free Methylammonium Alkaline-Earth Perovskite Based on DFT Calculations

Dynamical stability plays an essential role in phase transition and structure, and it could be a fundamental method of discovering new lead-free perovskite materials. The perovskite materials are well-known for their excellent optoelectronic properties, but the lead element inside could be a hindrance to future development. This research is trying to predict the promising cation candidates in the high-temperature application for lead-free perovskite materials from the replacement of lead in MAPbCl₃ (MA = methylammonium) with alkaline-earth cations. The alkaline-earth cations are of a stable positive divalent sort, which is the same as Pb, and most of them are abundant in nature. Therefore, by improving the dynamical stability, the Mg²⁺, Ca²⁺, and Sr²⁺ cations replacement of lead ions could stabilize the perovskite structure by decreasing the imaginary part of phonon density of states. Finally, the density functional theory results show that the MACaCl₃ could be a dynamic stable lead-free methylammonium perovskite material with an ultrawide band gap (5.96 eV).

Experimental and theoretical study of europium-doped organometal halide perovskite nanoplatelets for UV photodetection with high responsivity and fast response

Herein, we investigate the role of Eu³⁺ doping on CH₃NH₃PbBr₃ nanoplatelets (NPLs) in terms of their optoelectronic properties and photodetection application through a combined experimental and theoretical approach. The introduction of EuCl₃ in the CH₃NH₃PbBr₃ crystal structure by a facile solvothermal method enabled the tuning of the lateral and vertical dimensions of the NSs to form large-area NPLs and finally monolayer nanocrystals. The appearance of low-angle diffraction peaks with Eu doping, which are observed in layered perovskite structures, confirms the formation of quasi-2D NPLs. The bandgap of the Eu-doped mixed halide perovskite systematically increases from 2.39 eV to 2.94 eV with increasing doping concentration. Interestingly, 10 mol% EuCl₃ doping in the pure CH₃NH₃PbBr₃ crystal dramatically enhances its absorbance and photosensitivity, resulting in high-performance photodetection. Under 405 nm excitation, the CH₃NH₃Pb_0.9Eu_0.1Br_2.7Cl_0.3 photodetector exhibits self-biased behavior with an on/off ratio >10³, which is very significant. The planar device achieves a responsivity as high as 5.29 A W^- and a detectivity of 1.06 × 10¹² Jones under 405 nm with a power density of 0.14 mW cm^-2 at 5 V. In addition, the device exhibits very fast response time with a rise/fall time of 17.5/38.5 μs, which is ∼4 times faster than the pristine CH₃NH₃PbBr₃ counterpart. A linear relationship of photocurrent with light intensity in the CH₃NH₃Pb_0.9Eu_0.1Br_2.7Cl_0.3 photodetector signifies low recombination or charge trapping loss. High-performance photodetection in the Eu-doped device is ascribed to the elimination of trap states and the fast charge transfer process. To obtain better insight into the doped system, DFT analysis of the electronic structure of EuCl₃-doped CH₃NH₃PbBr₃ was performed and the results are fully consistent with the experimental findings. It was revealed that EuCl₃ doping increases the density of states near the conduction band along with a blue shift in the bandgap as compared to that of the pristine perovskite, which in turn increases the built-in potential of the fabricated device, resulting in self-biased photodetection. This work paves the way for deeper understanding of lanthanide doping in perovskites and self-biased photodetection applications of a new family of Eu-doped mixed halide perovskite nanostructures.

Electronic and optical properties of orthorhombic (CH3NH3)BX3 (B = Sn, Pb; X = F, Cl, Br, I) perovskites: a first-principles investigation

Lead halide perovskites have generated considerable interest in solar cell, sensor, and electronics applications. While great focus has been placed on (CH₃NH₃)PbI₃, an organic–inorganic hybrid perovskite, comparatively little work has been done to understand some of its existing crystal phases and analogous materials after substituting with Sn and/or other halogens in the framework. Here, first-principles density functional theory calculations are performed to comprehensively evaluate the electronic and optical properties of (CH₃NH₃)BX₃ (B = Sn, Pb; X = F, Cl, Br, I) in a low-temperature orthorhombic phase. Bulk modulus, electronic structures, and several optical properties of these perovskite systems are further calculated. The obtained results are first confirmed by comparing with existing perovskite systems in literature. The shifting trends on those physical properties when extending to other barely studied systems of (CH₃NH₃)BX₃ is further revealed. The band gap of these perovskites is found to decrease when varying halogen anion in “X” sites from F to I, and/or substituting Pb cations with Sn in “B” sites. Notably, the less toxic Sn-containing perovskites, (CH₃NH₃)SnI₃ in particular, display higher absorption coefficients in the visible light range than their Pb-containing counterparts. An orthorhombic (CH₃NH₃)PbF₃ is predicted to exist at low temperature, and adsorb strongly UV energy. Our systematical examination efforts on the two groups of perovskites provide valuable physical insights in these materials, and the accompanied new findings warrant further investigation on such subjects.

The electronic and optical properties of orthorhombic (CH₃NH₃)BX₃ (B = Sn, Pb; X = F, Cl, Br, I) were investigated by first-principles density functional theory.