Valence and Conduction Band Densities of States of Metal Halide Perovskites: A Combined Experimental–Theoretical Study

Endres, James; Egger, David; Kulbak, Michael; Kerner, Ross A.; Zhao, Lianfeng; Silver, Scott; Hodes, Gary; Rand, Barry P.; Cahen, David; Kronik, Leeor; Kahn, Antoine

doi:10.1021/acs.jpclett.6b00946

Cited by 365 publications

(448 citation statements)

References 58 publications

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“…We shall now discuss the implications of these findings on the electronic properties of this material. The key contributions to the edges of the band structure come from the hybridization of the 5p orbitals of iodine and 6s orbitals of lead for the valence band, and the empty 6p orbitals of lead for the conduction band 5,60 . While the MA cation does not contribute directly to the band structure, the coupling between the motion of the molecule and the structure of the inorganic components makes it a key influence upon the electronic response, and hence upon the photovoltaic properties.…”

Section: Discussionmentioning

confidence: 99%

Molecular orientational melting within a lead-halide octahedron framework: The order-disorder transition in CH3NH3PbBr3

et al. 2017

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Lead-halide organic-inorganic perovskites consist of an inorganic host framework with an organic molecule occupying the interstitial space. The structure and dynamics of these materials have been heavily studied recently due to interest in their exceptional photovoltaic properties. We combine inelastic neutron scattering, Raman spectroscopy, and quasielastic neutron scattering to study the temperature dependent dynamics of the molecular cation in CH3NH3PbBr3. By applying high resolution quasielastic neutron scattering, we confirm the [CH3NH3]+ ions are static in the low temperature orthorhombic phase yet become dynamic above 150 K where a series of structural transitions occur. This molecular melting is accompanied by a temporal broadening in the intra-molecular modes probed through high energy inelastic spectroscopy. Simultaneous Raman measurements, a strictly |Q|=0 probe, are suggestive that this broadening is due to local variations in the crystal field environment around the hydrogen atoms. These results confirm the strong role of hydrogen bonding and also a coupling between molecular and framework dynamics.

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Section: Discussionmentioning

confidence: 99%

Molecular orientational melting within a lead-halide octahedron framework: The order-disorder transition in CH3NH3PbBr3

et al. 2017

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“…163,178 In the same way, the bandgaps and band offsets have been determined for MAPbBr 3 and CsPbBr 3 compounds. 177 It is important to note that the optical bandgap determined from optical characterization is prone to its own set of measurement and analysis errors. These could lead to inaccurate estimates of the conduction band minimum position.…”

Section: Complementary Techniques To Photoemission Spectroscopymentioning

confidence: 99%

Perovskite-Inspired Photovoltaic Materials: Toward Best Practices in Materials Characterization and Calculations

et al. 2017

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ABSTRACT:Recently, there has been an explosive growth in research based on hybrid lead-halide perovskites for photovoltaics owing to rapid improvements in efficiency. The advent of these materials for solar applications has led to widespread interest in understanding the key enabling properties of these materials. This has resulted in renewed interest in related compounds and a search for materials that may replicate the defect-tolerant properties and long lifetimes of the hybrid lead-halide perovskites. Given the rapid pace of development of the field, the rises in efficiencies of these systems have outpaced the more basic understanding of these materials. Measuring or calculating the basic properties, such as crystal/electronic structure and composition, can be challenging because some of these materials have anisotropic structures, and/or are composed of both heavy metal cations and volatile, mobile, light elements. Some consequences are beam damage during characterization, composition change under vacuum, or compound effects, such as the alteration of the electronic structure through the influence of the substrate. These effects make it challenging to understand the basic properties integral to optoelectronic operation. Compounding these difficulties is the rapid pace with which the field progresses. This has created an ongoing need to continually evaluate best practices with respect to characterization and calculations, as well as to identify inconsistencies in reported values to determine if those inconsistencies are rooted in characterization methodology or materials synthesis. This article describes the difficulties in characterizing hybrid lead-halide perovskites and new materials, and how these challenges may be overcome. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 2 challenges discussed. The focus in this article is on crystallography, composition measurements, photoemission spectroscopy and calculations on perovskites and new, related absorbers. We suggest how some of the important artifacts could be avoided and how the reporting for each technique could be streamlined between groups to ensure reproducibility as the field progresses.

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“…(E − E E1 ) 2 reflects the joint density of states, which gives the emission spectrum after multiplication with the high-energy tail exp (−E/kT * ) of a Fermi-Diraclike distribution. The parabolic density of states is introduced here empirically, since it gives a better fit to the data than the square-root function expected for a threedimensional electron gas, as found also in photoemission experiments [53,72]. Fits to the data are shown in Fig.…”

Section: Modeling Of Absorption and Emission Spectramentioning

confidence: 99%

Temperature-dependent optical spectra of single-crystal (CH3NH3)PbBr3 cleaved in ultrahigh vacuum

et al. 2017

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We measure temperature-dependent one-photon and two-photon induced photoluminescence from (CH3NH3)PbBr3 single crystals cleaved in ultrahigh vacuum. An approach is presented to extract absorption spectra from a comparison of both measurements. Cleaved crystals exhibit broad photoluminescence spectra. We identify the direct optical band gap of 2.31 eV. Below 200 K the band gap increases with temperature, and it decreases at elevated temperature, as described by the BoseEinstein model. An excitonic transition is found 22 meV below the band gap at temperatures < 200 K. Defect emission occurs at photon energies < 2.16 eV. In addition, we observe a transition at 2.25 eV (2.22 eV) in the orthorhombic (tetragonal and cubic) phase. Below 200 K, the associated exciton binding energy is also 22 meV, and the transition redshifts at higher temperature. The binding energy of the exciton related to the direct band gap, in contrast, decreases in the cubic phase. High-energy emission from free carriers is observed with higher intensity than reported in earlier studies. It disappears after exposing the crystals to air.

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Valence and Conduction Band Densities of States of Metal Halide Perovskites: A Combined Experimental–Theoretical Study

Cited by 365 publications

References 58 publications

Molecular orientational melting within a lead-halide octahedron framework: The order-disorder transition in CH3NH3PbBr3

Molecular orientational melting within a lead-halide octahedron framework: The order-disorder transition in CH3NH3PbBr3

Perovskite-Inspired Photovoltaic Materials: Toward Best Practices in Materials Characterization and Calculations

Temperature-dependent optical spectra of single-crystal (CH3NH3)PbBr3 cleaved in ultrahigh vacuum

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