Halide double perovskites have recently been developed as less toxic analogs of the lead perovskite solar-cell absorbers APbX3 (A = monovalent cation; X = Br or I). However, all known halide double ...perovskites have large bandgaps that afford weak visible-light absorption. The first halide double perovskite evaluated as an absorber, Cs2AgBiBr6 (1), has a bandgap of 1.95 eV. Here, we show that dilute alloying decreases 1’s bandgap by ca. 0.5 eV. Importantly, time-resolved photoconductivity measurements reveal long-lived carriers with microsecond lifetimes in the alloyed material, which is very promising for photovoltaic applications. The alloyed perovskite described herein is the first double perovskite to show comparable bandgap energy and carrier lifetime to those of (CH3NH3)PbI3. By describing how energy- and symmetry-matched impurity orbitals, at low concentrations, dramatically alter 1’s band edges, we open a potential pathway for the large and diverse family of halide double perovskites to compete with APbX3 absorbers.
The Diversity of Layered Halide Perovskites Smith, Matthew D; Crace, Ethan J; Jaffe, Adam ...
Annual review of materials research,
07/2018, Letnik:
48, Številka:
1
Journal Article
Recenzirano
The two-dimensional congeners of the well-known three-dimensional perovskites display new properties enabled by their reduced dimensionality. Here, organic molecules separate inorganic sheets, ...affording the properties of both discrete molecules and extended solids in single, well-defined materials. The choice of organic and inorganic components engenders a large range of structural motifs, which yield diverse properties such as electroluminescence, white-light emission, photoconductivity, porosity, and reactivity. Layered halide perovskites have been known for decades. Their recent resurgence compels us to understand the fundamental studies that set the stage for their current technological relevance. We are not providing a comprehensive review of this vast and rapidly growing field. Instead, we highlight some of the discoveries that have directed current research in this field. We hope to introduce new researchers to layered halide perovskites to bring fresh perspectives to study this venerable family of materials that continue to surprise us today.
Pressure-induced changes in the electronic structure of two-dimensional Cu-based materials have been a subject of intense study. In particular, the possibility of suppressing the Jahn–Teller ...distortion of d9 Cu centers with applied pressure has been debated over a number of decades. We studied the structural and electronic changes resulting from the application of pressures up to ca. 60 GPa on a two-dimensional copper(II)–chloride perovskite using diamond anvil cells (DACs), through a combination of in situ powder X-ray diffraction, electronic absorption and vibrational spectroscopy, dc resistivity measurements, and optical observations. Our measurements show that compression of this charge-transfer insulator initially yields a first-order structural phase transition at ca. 4 GPa similar to previous reports on other CuII–Cl perovskites, during which the originally translucent yellow solid turns red. Further compression induces a previously unreported phase transition at ca. 8 GPa and dramatic piezochromism from translucent red-orange to opaque black. Two-probe dc resistivity measurements conducted within the DAC show the first instance of appreciable conductivity in CuII–Cl perovskites. The conductivity increases by 5 orders of magnitude between 7 and 50 GPa, with a maximum measured conductivity of 2.9 × 10–4 S·cm–1 at 51.4 GPa. Electronic absorption spectroscopy and variable-temperature conductivity measurements indicate that the perovskite behaves as a 1.0 eV band-gap semiconductor at 39.7 GPa and has an activation energy for electronic conduction of 0.232(1) eV at 40.2 GPa. Remarkably, all these changes are reversible: the material reverts to a translucent yellow solid upon decompression, and ambient pressure powder X-ray diffraction data taken before and after compression up to 60 GPa show that the original structure is maintained with minimal hysteresis.
The impressive rise in efficiencies of solar cells employing the three-dimensional (3D) lead–iodide perovskite absorbers APbI3 (A = monovalent cation) has generated intense excitement. Although these ...perovskites have remarkable properties as solar-cell absorbers, their potential commercialization now requires a greater focus on the materials’ inherent shortcomings and environmental impact. This creates a challenge and an opportunity for synthetic chemists to address these issues through the design of new materials. Synthetic chemistry offers powerful tools for manipulating the magnificent flexibility of the perovskite lattice to expand the number of functional analogues to APbI3. To highlight improvements that should be targeted in new materials, here we discuss the intrinsic instability and toxicity of 3D lead–halide perovskites. We consider possible sources of these instabilities and propose methods to overcome them through synthetic design. We also discuss new materials developed for realizing the exceptional photophysical properties of lead–halide perovskites in more environmentally benign materials. In this Forum Article, we provide a brief overview of the field with a focus on our group’s contributions to identifying and addressing problems inherent to 3D lead–halide perovskites.
We investigate the consequences of dimensional confinement on halide double perovskites by synthesizing two-dimensional analogues of the recently reported three-dimensional double perovskite ...Cs2AgBiBr6. The layered perovskites (BA)4AgBiBr8 (1) and (BA)2CsAgBiBr7 (2) (BA = CH3(CH2)3NH3 +) feature metal-halide sheets of mono and bilayer thickness, respectively, where the ordered double-perovskite lattice is partitioned by organic cations. Electronic structure calculations indicate that the indirect bandgap of Cs2AgBiBr6 becomes direct when the infinitely thick inorganic lattice is reduced to monolayer thickness. Calculations on model systems allow us to separate the effects of dimensional reduction from those of the accompanying structural distortions in the inorganic sublattice. Detailed optical characterization shows that the photophysical properties of 1 and 2 are markedly different than those of their well-studied lead-halide analogs. Hybrid layered derivatives of double perovskites substantially expand on the substitutional flexibility of halide perovskites to encompass greater compositional and electronic diversity.
Hybrid halide perovskites are promising for applications because of their favorable optoelectronic properties and low cost. Here we investigate the effects of hydrostatic pressure on the structural ...and electronic properties of (MA)PbI3 (MA = CH3NH3 +) using first-principles density functional theory calculations. Our calculations predict that at a pressure of 0.23 GPa, the orthorhombic Fmmm phase becomes unstable with respect to a cubic Im3̅ phase, in good agreement with room-temperature experiments (∼0.3 GPa). At higher pressures, about 6 GPa, we predict the onset of pronounced intra- and interoctahedral distortions. This symmetry lowering leads to the introduction of I 5p–I 5p* antibonding and Pb 6p–Pb 6p bonding character into the valence band maximum (VBM) and the conduction band minimum (CBM) states, respectively. We find this change in bond character explains the evolution of the VBM and CBM states under compression, trends that ultimately lead to metallization at significantly higher pressures.
The recently discovered phenomenon of broadband white-light emission at room temperature in the (110) two-dimensional organic–inorganic perovskite (N-MEDA)PbBr4 (N-MEDA = N ...1-methylethane-1,2-diammonium) is promising for applications in solid-state lighting. However, the spectral broadening mechanism and, in particular, the processes and dynamics associated with the emissive species are still unclear. Herein, we apply a suite of ultrafast spectroscopic probes to measure the primary events directly following photoexcitation, which allows us to resolve the evolution of light-induced emissive states associated with white-light emission at femtosecond resolution. Terahertz spectra show fast free carrier trapping and transient absorption spectra show the formation of self-trapped excitons on femtosecond time-scales. Emission-wavelength-dependent dynamics of the self-trapped exciton luminescence are observed, indicative of an energy distribution of photogenerated emissive states in the perovskite. Our results are consistent with photogenerated carriers self-trapped in a deformable lattice due to strong electron–phonon coupling, where permanent lattice defects and correlated self-trapped states lend further inhomogeneity to the excited-state potential energy surface.
When the stakes are doubled in a wager, a player must correctly place two consecutive bets to win, but the payout is larger. Similarly, two B sites in combination dictate the properties of A2BB′X6 ...(A=monocation, X=halide) double perovskites. Correctly picking two B sites is more challenging than picking just one, as in the AIBIIX3 single perovskites, but the options are greater and, we believe, the rewards are higher when the stakes are doubled. In this Minireview, we emphasize fundamental aspects of halide double perovskites to provide a foundation for interested readers to explore this extraordinary class of materials. In particular, we highlight the differences and similarities between double and single perovskites and describe how the double perovskite structure potentially offers greater control over photophysical properties.
Two B sites in combination dictate the properties of halide double perovskites (A2BB′X6; A=monocation, X=halide). This Minireview gives a brief overview of the rich history of halide double perovskites, highlights key structural and electronic aspects, and describes the current understanding on how to correctly select the B‐site pairs that afford the desired properties.
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