X-ray photon detection is important for a wide range of applications. The highest demand, however, comes from medical imaging, which requires cost-effective, high-resolution detectors operating at low photon flux, therefore stimulating the search for novel materials and new approaches. Recently, hybrid halide perovskite CH3NH3PbI3 (MAPbI3) has attracted considerable attention due to its advantageous optoelectronic properties and low fabrication costs. The presence of heavy atoms, providing a high scattering cross-section for photons, makes this material a perfect candidate for X-ray detection. Despite the already-successful demonstrations of efficiency in detection, its integration into standard microelectronics fabrication processes is still pending. Here, we demonstrate a promising method for building X-2 ray detector units by 3D aerosol jet printing with a record sensitivity of 2.2 x 10 8 µC Gyair -1 cm -2 when detecting 8 keV photons at dose-rates below 1 Gy/s (detection limit 0.12 Gy/s), a fourfold improvement on the best-in-class devices. An introduction of MAPbI3-based detection into medical imaging would significantly reduce health hazards related to the strongly ionizing Xrays photons.
Organic−inorganic metal halide perovskites have recently attracted increasing attention as highly efficient light harvesting materials for photovoltaic applications. The solution processability of these materials is one of their major advantages on the route toward fabrication of low-cost solar cells and optoelectronic devices. However, the precise control of crystallization and morphology of organometallic perovskites deposited from solutions, considered crucial for enhancing the final photovoltaic performance, still remains challenging. In this context, here, we report on growing microcrystalline deposits of methylammonium lead triiodide perovskite, CH3NH3PbI3 (MAPbI3), by one-step solution casting on cylinder-shaped quartz substrates (rods) having diameters in the range of 80 to 1800 μm. We show that the substrate curvature has a strong influence on morphology of the obtained polycrystalline deposits of MAPbI3. Specifically, a marked size reduction of MAPbI3 microcrystallites concomitant with an increased crystal packing density was observed with increasing the substrate curvatures. In contrast, although the crystallite width and length markedly decreased for substrates with higher curvatures, the photoluminescence (PL) spectral peak positions did not significantly evolve for MAPbI3 deposits on substrates with different diameters. The crystallite size reduction and a denser coverage of microcrystalline MAPbI3 deposits on cylinder-shaped substrates with higher curvatures were attributed to two major contributions, both related to the annealing step of the MAPbI3 deposits. In particular, the diameter-dependent variability of the heat capacities and the substrate curvature-enhanced solvent evaporation rate seemed to contribute the most to the crystallization process and the resulting morphology changes of MAPbI3 deposits on cylinder-shaped quartz substrates with various diameters. The longitudinal geometry of cylinder-shaped substrates provided also a facile solution for checking the PL response of the deposits of MAPbI3 exposed to the flow of various gaseous media, such as oxygen (O2), nitrogen (N2), and argon (Ar). Specifically, under excitation with λexc = 546 nm, the rapid and pronounced decreases and increases of PL signals were observed under intermittent subsequent exposures to O2 and N2, respectively. Overall, the approach reported herein inspires novel, cylinder-shaped geometries of MAPbI3 deposits, which can find applications in low-cost photo-optical devices, including gas sensors.
Because of their excellent photoelectric properties, organic−inorganic metal halide perovskites (MHPs), such as methylammonium lead triiodide, CH 3 NH 3 PbI 3 (MAPbI 3 ), and methylammonium lead tribromide, CH 3 NH 3 PbBr 3 (MAPbBr 3 ), are of great interest for the emerging MHPs-based photovoltaic technology. Despite extensive research efforts focused on physicochemical aspects of both MAPbI 3 and MAPbBr 3 , the impact of environmental extremes, including various gaseous media, on their photoelectric properties remains poorly understood. In this context, here, the MHPs-based gas-sensing elements were grown by one-step solution process on the outer surface of cylindrical in shape quartz substrates with diameters varying in the range of 80−1100 μm. The elongated cylinder-shaped geometry and high surface-to-volume ratios of the thus-prepared deposits revealed advantageous for designing miniature, light-transparent gas-flow chambers and made it possible to investigate the photoluminescence (PL) and photocurrent (PC) responses of both MHPs exposed to the precisely controlled recurrent flow of either O 2 or N 2 . In addition, we could also collect the PL responses for the deposits of MAPbI 3 and MAPbBr 3 , positioned side-by-side close to each other and therefore simultaneously exposed to identical environmental conditions. Specifically, we found that under exposure to O 2 the PL responses of MAPbI 3 and MAPbBr 3 were markedly opposite; i.e., the PL decreased for MAPbI 3 , whereas it increased for MAPbBr 3 . In contrast, under the exposure to N 2 , the PL of MAPbI 3 increased, while it decreased for MAPbBr 3 . A considerably differential behavior was also found for the PC responses. In particular, under recurrent exposures to both gaseous media, the PL and PC responses of MAPbBr 3 correlated, whereas for MAPbI 3 they anticorrelated. In conclusion, the distinctly opposite PL and PC responses of polycrystalline deposits of MAPbI 3 and MAPbBr 3 to O 2 and N 2 reported herein point to markedly contrasting properties of the surface carrier traps and defects for these two MHPs. This study also evidences that a side-by-side arrangement of elongated cylindrically shaped substrates coated with two different MHPs, due to their differential responses to exposure to O 2 or N 2 , can function as a simple differential gas detector.
Optoelectronic devices and solar cells based on organometallic hybrid perovskites have to operate over a broad temperature range, which may contain their structural phase transitions. For instance, the temperature of 330 K, associated with the tetragonal–cubic transformation, may be crossed every day during the operation of solar cells. Therefore, the analysis of thermal cycling effects on structural and electronic properties is of significant importance. This issue is addressed in the case of methylammonium lead iodide (CH3NH3PbI3) across both structural phase transitions (at 160 and 330 K). In situ synchrotron radiation X‐ray diffraction (XRD) data recorded between 140 and 180 K show the emergence of a boundary phase between the orthorhombic and tetragonal phases, which becomes more abundant with successive thermal cycles. At high temperatures, around 330 K, an incommensurately modulated tetragonal phase is formed upon repeated crossings of the phase boundary between tetragonal and cubic phases. These alterations, which indicate a gradual evolution of the material under operating conditions of photovoltaic devices, are further documented by electrical resistivity and heat capacity measurements.
The photovoltaic perovskite, methylammonium lead triiodide [CH3NH3PbI3 (MAPbI3)], is one of the most efficient materials for solar energy conversion. Various kinds of chemical and physical modifications have been applied to MAPbI3 towards better understanding of the relation between composition, structure, electronic properties and energy conversion efficiency of this material. Pressure is a particularly useful tool, as it can substantially reduce the interatomic spacing in this relatively soft material and cause significant modifications to the electronic structure. Application of high pressure induces changes in the crystal symmetry up to a threshold level above which it leads to amorphization. Here, a detailed structural study of MAPbI3 at high hydrostatic pressures using Ne and Ar as pressure transmitting media is reported. Single-crystal X-ray diffraction experiments with synchrotron radiation at room temperature in the 0–20 GPa pressure range show that atoms of both gaseous media, Ne and Ar, are gradually incorporated into MAPbI3, thus leading to marked structural changes of the material. Specifically, Ne stabilizes the high-pressure phase of Ne x MAPbI3 and prevents amorphization up to 20 GPa. After releasing the pressure, the crystal has the composition of Ne0.97MAPbI3, which remains stable under ambient conditions. In contrast, above 2.4 GPa, Ar accelerates an irreversible amorphization. The distinct impacts of Ne and Ar are attributed to differences in their chemical reactivity under pressure inside the restricted space between the PbI6 octahedra.
The performance of organic-inorganic metal halide perovskites-based (MHPs) photovoltaic devices critically depends on the design and material properties of the interface between the light-harvesting MHP layer and the electron transport layer (ETL). Therefore, the detailed insight into the transfer mechanisms of photogenerated carriers at the ETL/MHP interface is of utmost importance. Owing to its high charge mobilities and well-matched band structure with MHPs, titanium dioxide (TiO 2 ) has emerged as the most widely used ETL material in MHPs-based photovoltaic devices. Here, we report a contactless method to directly track the photo-carriers at the ETL/MHP interface using the technique of low-temperature electron paramagnetic resonance (EPR) in combination with in situ illuminations (Photo-EPR). Specifically, we focus on a model nanohybrid material consisting of TiO 2 -based nanowires (TiO 2 NWs) dispersed in the polycrystalline methylammonium lead triiodide (MAPbI 3 ) matrix. Our approach is based on observation of the light-induced decrease in intensity of the EPR signal of paramagnetic Ti 3+ ( = S 1 2) in non-stoichiometric TiO 2 NWs. We associate the diminishment of the EPR signal with the photo-excited electrons that cross the ETL/MHP interface and contribute to the conversion of Ti 3+ states to EPR-silent Ti 2+ states. Overall, we infer that the technique of lowtemperature Photo-EPR is an effective strategy to study the transfer mechanisms of photogenerated carriers at the ETL/MHP interface in MAPbI 3 -based photovoltaic and photoelectronic systems.
We report the synthesis, crystal structure, and photoconductivity of EDPbI4. The ED disorder depends on the thermal treatment of EDPbI4. The increased disorder is associated with increased photoconductivity.
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