Bismuth Doping Alters Structural Phase Transitions in Methylammonium Lead Tribromide Single Crystals

Sensitive Thermography via Sensing Visible Photons Detected from the Manipulation of the Trap State in MAPbX3

Sensitive thermometry or thermography by responding to blackbody radiation is urgently desired in the intelligent information life, including scientific research, medical diagnosis, remote sensing, defense, etc. Even though thermography techniques based on infrared sensing have undergone unprecedented development, the poor compatibility with common optical components and the high diffraction limit impose an impediment to their integration into the established photonic integrated circuit or the realization of high-spatial-resolution and high-thermal-resolution imaging. In this work, we present a sensitive temperature-dependent visible photon detection in Bi-doped MAPbX3 (X = Cl, Br, and I) and employ it for uncooled thermography. Systematic measurements reveal that the Bi dopant introduces trap states in MAPbX3, thermal energy facilitates the carriers jumping from trap states to the conduction band, while the vacancies of trap states ensure the sequential absorption of visible photons with energy less than the band gap. Subsequently, the change of response toward the visible photon is applied to construct the thermograph, and it possesses a specific sensitivity of 2.11% K-1 along temperature variation. As a result, our thermograph presents a temperature resolution of 0.21 nA K-1, a high responsivity of 2.06 mA W-1, and a high detectivity of 2.08 × 109 Jones at room temperature. Furthermore, remote thermal imaging is successfully achieved with our thermograph.

Quantum Dot Metal Salt Interactions Unraveled by the Sphere of Action Model

Postsynthetic metal salt treatments are frequently employed in the luminescence enhancement of quantum dots (QDs); however, its microscopic picture remains unclear. CsPbBr₃-QDs, featuring strong excitonic absorption and high photoluminescence (PL) quantum yield, are ideal QDs to unravel the intricate interaction between QDs and such surface-bound metal salts. Herein, we study this interaction based on the controlled PL quenching of CsPbBr₃-QDs with BiBr₃. Upon the addition of BiBr₃, an instant and complete PL quenching is observed, which can be fully recovered after the addition of an excess of PbBr₂. This, together with the complete preservation of the excitonic absorption suggests a surface-driven adsorption equilibrium. Additionally, time-resolved studies reveal a non-homogeneous surface trap formation. Based on the so-called sphere of action model for the adsorption process, we show that already a single BiBr₃ adsorption suffices to completely quench a QD's luminescence. This approach is expanded to analyze size-, ligand-, and metal-dependent quenching dynamics. Facet junctions are identified as regions of enhanced surface reactivity. A Langmuir-type ligand coverage is exposed with a strong impact on adsorption. Our results provide a detailed mechanistic insight into postsynthetic interaction of QDs with metal salts, opening pathways for future surface manipulations.

Optimized photoelectric characteristics of MAPbCl3and MAPbBr3composite perovskite single crystal heterojunction photodetector

MAPbBr₃single crystal (SC) thin layer was successfully grown on MAPbCl₃SC substrate to form perovskite SC heterojunction. Planar structure electrodes are deposited by thermal evaporation on the surfaces of MAPbCl₃, MAPbBr₃, and SCs heterojunction, respectively to evaluate their photoelectric performance. The SC heterojunction device exhibits excellent unidirectional conductivity in the voltage-current curves. Meanwhile, the current-time curves prove that SC heterojunction devices can effectively utilize the advantages of MAPbCl₃and MAPbBr₃, possessing relatively low dark current (∼300 nA), which is comparable to the dark current of MAPbCl₃, but very high photocurrent (∼3500 nA), which is equivalent to the photocurrent of MAPbBr₃. Rather than the photocurrent overshot and decay occurring at the exposure of light illumination in the MAPbBr₃device, the photocurrent is extremely stable without overshot and decay in the SC heterojunction device. The light-to-dark ratio of the SC heterojunction device is twice that of MAPbCl₃device and three times that of MAPbBr₃device. Furthermore, the detectivity of the heterojunction device reaches as high as∼7×1011 Jones, an order of magnitude higher than MAPbCl₃and MAPbBr₃. The excellent characteristics of SC heterojunction further expand the practical application prospect of perovskite materials.

Rietveld Refinement, Morphology, and Optical and Photoluminescence Properties of a β-Ag1.94Cu0.06MoO4 Solid Solution

Corner-truncated cubic β-Ag_1.94Cu_0.06MoO₄ microcrystals were synthesized using the hydrothermal method. These were investigated by X-ray diffraction, confirming obtention of the spinel structure Fd3̅m. Through Raman spectroscopy are confirmed all modes for the point group of O_h⁷. The E_gap shows a decrease of the band gap from 3.20 to 3.07 eV, with reduction of the conduction band occurring from -0.20 eV (β-Ag₂MoO₄) to -0.13 eV (β-Ag_1.94Cu_0.06MoO₄), suggesting a p-type behavior for the Cu²⁺ ion. The field-emission scanning electron microscopy images confirm the morphological changes for β-Ag₂MoO₄, where potato-like microcrystals were found. Meanwhile, corner-truncated cubic microcrystals for β-Ag_1.94Cu_0.06MoO₄. The photoluminescence (PL) spectrum confirms the increase in the PL emission for β-Ag_1.94Cu_0.06MoO₄, with suppression of the deep defects occurring in the structure caused by oxygen and silver atoms. In contrast, the green region is intensified because of distortions of the Ag-O and Mo-O bonds. Therefore, the β-Ag_1.94Cu_0.06MoO₄ solid solution has PL emission with CCT (4510 K) and CIE coordinates (x = 0.372 and y = 0.433), which could be interesting properties for applications as light-emitting diodes.

Impact of Bi Doping on Nonradiative Carrier Recombination in CsPbI3

Bi doping is attractive in lead halide perovskites due to the potential ability of narrowing band gap and improving structural stability. Nevertheless, whether Bi acts as a nonradiative recombination center...

Trojans That Flip the Black Phase: Impurity-Driven Stabilization and Spontaneous Strain Suppression in γ-CsPbI3 Perovskite

The technological progress and widespread adoption of all-organic CsPbI₃ perovskite devices is hampered by its thermodynamic instability at room temperature. Because of its inherent tolerance toward deep trap formation, there has been no shortage to exploring which dopants can improve the phase stability. While the relative size of the dopant is important, an assessment of the literature suggests that its relative size and impact on crystal volume do not always reveal what will beneficially shift the phase transition temperature. In this perspective, we analyze the changes in crystal symmetry of CsPbI₃ perovskite as it transforms from a thermodynamically stable high-temperature cubic (α) structure into its distorted low-temperature tetragonal (β) and unstable orthorhombic (γ) perovskite structures. Quantified assessment of the symmetry-adapted strains which are introduced due to changes in temperature and composition show that the stability of γ-CsPbI₃ is best rationalized from the point of view of crystal symmetry. In particular, improved thermal-phase stability is directly traced to the suppression of spontaneous strain formation and increased crystal symmetry at room temperature.