Ultrathin halide perovskites have drawn tremendous attention in nano‐/micro‐optoelectronic devices due to their fascinating performance and capability for chip integration. Unfortunately, it is ...highly challenging to obtain large‐scale and chronically stable ultrathin halide perovskites for practical application. Herein, the universal low‐temperature vapor‐phase synthesis of ultrathin perovskite family materials with thickness down to 2D level and lateral size up to 1.5 cm × 1.5 cm is reported by developing a self‐limiting chemical vapor deposition strategy. The perovskite products are found to exhibit superior stability over 180 days under an air environment. The resultant photodetectors demonstrate charming optoelectronic properties such as superior responsivity (3.7 × 103 A W−1), ultrafast response time (<10 µs), and outstanding low‐level light image sensing capability. This universal perovskite synthesis strategy offers great potential for practical applications of halide perovskites in future nano‐/micro‐optoelectronic devices.
A universal vapor‐phase synthesis method is developed to realize the growth of various halide perovskites (e.g., MAPbBr3, FAPbBr3, MAPbI3, FAPbI3, and Cs4PbI6) with lateral size up to 1.5 cm × 1.5 cm and long‐term stability over 180 days under air‐environment. The resultant perovskite photodetectors exhibit attractive optoelectronic properties such as superior responsivity, ultrafast response time, and outstanding photoelectric image sensing capability.
The sulfone-functionalized Zr- and Hf-UiO-67 metal–organic frameworks with hierarchical mesopores were successfully synthesized using the ligand 4,4′-dibenzoic acid-2,2′-sulfone, with acetic acid or ...HCl as the modulator. Compared to UiO-67, the zirconium solid shows a remarkable 122% increase in CO2 uptake, reaching 4.8 mmol g–1 (17.4 wt %) at 1 bar and 273 K (145% at 298 K) and more than 100% increase in CO2/CH4 selectivity.
The implementation of two-dimensional (2D) hybrid organic–inorganic perovskites (HOIPs) in semiconductor device applications will have to accommodate the co-existence of strain and temperature ...stressors and requires a thorough understanding of the thermomechanical behavior of 2D HOIPs. This will mitigate thermomechanical stability issues and improve the durability of the devices, especially when one considers the high susceptibility of 2D HOIPs to temperature due to their soft nature. Here, we employ atomic force microscopy (AFM) stretching of suspended membranes to measure the temperature dependence of the in-plane Young’s modulus (E ∥) of model Ruddlesden–Popper 2D HOIPs with a general formula of (CH3(CH2)3NH3)2(CH3NH3) n−1Pb n I3n+1 (here, n = 1, 3, or 5). We find that E ∥ values of these 2D HOIPs exhibit a prominent non-monotonic dependence on temperature, particularly an abnormal thermal stiffening behavior (nearly 40% change in E ∥) starting around the order–disorder transition temperature of the butylammonium spacer molecules, which is significantly different from the thermomechanical behavior expected from their 3D counterpart (CH3NH3PbI3) or other low-dimensional material systems. Further raising the temperature eventually reverses the trend to thermal softening. The magnitude of the thermally induced change in E ∥ is also much higher in 2D HOIPs than in their 3D analogs. Our results can shed light on the structural origin of the thermomechanical behavior and provide needed guidance to design 2D HOIPs with desired thermomechanical properties to meet the application needs.
PbTe-based thermoelectric materials are some of the most promising for converting heat into electricity, but their n-type versions still lag in performance the p-type ones. Here, we introduce midgap ...states and nanoscale precipitates using Ga-doping and GeTe-alloying to considerably improve the performance of n-type PbTe. The GeTe alloying significantly enlarges the energy band gap of PbTe and subsequent Ga doping introduces special midgap states that lead to an increased density of states (DOS) effective mass and enhanced Seebeck coefficients. Moreover, the nucleated Ga2Te3 nanoscale precipitates and off-center discordant Ge atoms in the PbTe matrix cause intense phonon scattering, strongly reducing the thermal conductivity (∼0.65 W m–1 K–1 at 623 K). As a result, a high room-temperature thermoelectric figure of merit ZT ∼ 0.59 and a peak ZTmax of ∼1.47 at 673 K were obtained for the Pb0.98Ga0.02Te-5%GeTe. The ZTavg value that is most relevant for devices is ∼1.27 from 400 to 773 K, the highest recorded value for n-type PbTe.
A recently discovered new family of 3D halide perovskites with the general formula (A)1–x (en) x (Pb)1–0.7x (X)3–0.4x (A = MA, FA; X = Br, I; MA = methylammonium, FA = formamidinium, en = ...ethylenediammonium) is referred to as “hollow” perovskites owing to extensive Pb and X vacancies created on incorporation of en cations in the 3D network. The “hollow” motif allows fine tuning of optical, electronic, and transport properties and bestowing good environmental stability proportional to en loading. To shed light on the origin of the apparent stability of these materials, we performed detailed thermochemical studies, using room temperature solution calorimetry combined with density functional theory simulations on three different families of “hollow” perovskites namely en/FAPbI3, en/MAPbI3, and en/FAPbBr3. We found that the bromide perovskites are more energetically stable compared to iodide perovskites in the FA-based hollow compounds, as shown by the measured enthalpies of formation and the calculated formation energies. The least stable FAPbI3 gains stability on incorporation of the en cation, whereas FAPbBr3 becomes less stable with en loading. This behavior is attributed to the difference in the 3D cage size in the bromide and iodide perovskites. Configurational entropy, which arises from randomly distributed cation and anion vacancies, plays a significant role in stabilizing these “hollow” perovskite structures despite small differences in their formation enthalpies. With the increased vacancy defect population, we have also examined halide ion migration in the FA-based “hollow” perovskites and found that the migration energy barriers become smaller with the increasing en content.
Chiral hybrid metal-halide semiconductors (MHS) pose as ideal candidates for spintronic applications owing to their strong spin–orbit coupling (SOC), and long spin relaxation times. Shedding light on ...the underlying structure–property relationships is of paramount importance for the targeted synthesis of materials with an optimum performance. Herein, we report the synthesis and optical properties of 1D chiral (R-/S-THBTD)SbBr5 (THBTD = 4,5,6,7-tetrahydro-benzothiazole-2,6-diamine) semiconductors using a multifunctional ligand as a countercation and a structure directing agent. (R-/S-THBTD)SbBr5 feature direct and indirect band gap characteristics, exhibiting photoluminescence (PL) light emission at RT that is accompanied by a lifetime of a few ns. Circular dichroism (CD), second harmonic generation (SHG), and piezoresponse force microscopy (PFM) studies validate the chiral nature of the synthesized materials. Density functional theory (DFT) calculations revealed a Rashba/Dresselhaus (R/D) spin splitting, supported by an energy splitting (E R) of 23 and 25 meV, and a Rashba parameter (αR) of 0.23 and 0.32 eV·Å for the R and S analogs, respectively. These values are comparable to those of the 3D and 2D perovskite materials. Notably, (S-THBTD)SbBr5 has been air-stable for a year, a record performance among chiral lead-free MHS. This work demonstrates that low-dimensional, lead-free, chiral semiconductors with exceptional air stability can be acquired, without compromising spin splitting and manipulation performance.
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