Absorption F-Sum Rule for the Exciton Binding Energy in Methylammonium Lead Halide Perovskites

Sestu, Nicola; Cadelano, Michele; Sarritzu, Valerio; Chen, Feipeng; Marongiu, Daniela; Piras, Roberto; Mainas, Marina; Quochi, Francesco; Saba, Michele; Mura, A.; Bongiovanni, Giovanni

doi:10.1021/acs.jpclett.5b02099

Cited by 153 publications

(206 citation statements)

References 37 publications

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“…Experimental studies have demonstrated that the onset of the optical absorption spectrum of tetragonal and orthorhombic MAPbI 3 shifts to higher energies as the temperatures increases. Also the Urbach energy increases, causing the optical spectrum to become less steep, with temperature [71,73,74]. Both facts suggest that the optical gap and the Urbach energy increase with the degree of disorder of the system.…”

Section: Discussionmentioning

confidence: 95%

Breathing bands due to molecular order in CH3NH3PbI3

Wierzbowska

Meléndez

Varsano

2018

Computational Materials Science

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CH 3 NH 3 PbI 3 perovskite is nowadays amongst the most promising photovoltaic materials for energy conversion. We have studied by ab-initio calculations, using several levels of approximation -namely density functional theory including spin-orbit coupling and quasi-particle corrections by means of the GW method, as well as pseudopotential self-interaction corrections-, the role of the methylammonium orientation on the electronic structure of this perovskite. We have considered many molecular arrangements within 2 × 2 × 2 supercells, showing that the relative orientation of the organic molecules is responsible for a huge band gap variation up to 2 eV. The band gap sizes are related to distortions of the PbI 3 cage, which are in turn due to electrostatic interactions between this inorganic frame and the molecules. The strong dependence of the band gap on the mutual molecular orientation is confirmed at all levels of approximations.Our results suggest then that the coupling between the molecular motion and the interactions of the molecules with the inorganic cage could help to explain the widening of the absorption spectrum of CH 3 NH 3 PbI 3 perovskite, consistent with the observed white spectrum.

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Section: Discussionmentioning

confidence: 95%

Breathing bands due to molecular order in CH3NH3PbI3

Wierzbowska

Meléndez

Varsano

2018

Computational Materials Science

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“…Given the large exciton binding energy measured for MAPbBr 3 SCs, excitons and free carriers are expected to coexist according to Saha-Langmuir equation. [27,41,42] For example, with typical excitation densities of around 10 16 -10 17 cm −3 for PL quenching experiments, free carrier population is found to be in the range of ≈50%-90% when trap states are not considered ( Figure S5a, Supporting Information). In addition, the initial emissive population (PL at t = 0) exhibits n ≈ 1.8 power law dependence with the pump excitation, which suggests the presence of both free carriers (n = 2) and excitons (n = 1) ( Figure S5b, Supporting Information).…”

Section: Optical Propertiesmentioning

confidence: 99%

“…[25,26] The profile is similar to previously reported absorption profiles of MAPbBr 3 nanocrystals and thin films, showing typical continuum band and excitonic absorptions. [27,28] Considering that the scattering varies slowly over a small frequency region, [25,26] we simply used the Elliott formula to extract the bandgap and exciton information in the SC (see the Supporting Information for the details of the fitting). [20] The extracted bandgap (E g ) value of 2.31 eV (continuum band-green curve) determined by diffuse reflectance is more accurate than that determined through absorption measurements as there is negligible high energy above bandgap light passing through the thick crystal ( Figure S1b, Supporting Information).…”

Section: Introductionmentioning

confidence: 99%

Discerning the Surface and Bulk Recombination Kinetics of Organic–Inorganic Halide Perovskite Single Crystals

Nguyen

et al. 2016

Advanced Energy Materials

284

331

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Organic–inorganic halide perovskite single crystals possess many outstanding properties conducive for photovoltaic and optoelectronic applications. However, a clear photophysics picture is still elusive, particularly, their surface and bulk photophysics are inexorably convoluted by the spectral absorbance, defects, coexisting photoexcited species, etc. In this work, an all‐optical study is presented that clearly distinguishes the surface kinetics from those of the bulk in the representative methylammonium‐lead bromide (MAPbBr3) and ‐lead iodide (MAPbI3) single crystals. It is found that the bulk recombination lifetime of the MAPbBr3 single crystal is shortened significantly by approximately one to two orders (i.e., from ≈34 to ≈1 ns) at the surface with a surface recombination velocity of around 6.7 × 103 cm s−1. The surface trap density is estimated to be around 6.0 × 1017 cm−3, which is two orders larger than that of the bulk (5.8 × 1015 cm−3). Correspondingly, the diffusion length of the surface excited species is ≈130–160 nm, which is considerably reduced compared to the bulk value of ≈2.6–4.3 μm. Furthermore, the surface region has a wider bandgap that possibly arises from the strong lattice deformation. The findings provide new insights into the intrinsic photophysics essential for single crystal perovskite photovoltaics and optoelectronic devices.

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“…One possible way to circumvent this is the so called f-sum rule, which uses the fact that the integral of the normalized absorption spectrum is independent from all parameters except the exciton binding energy. [18] It has been shown that the exciton binding energy of MAPbI 3 depends on various parameters, in particular, it is sensitive to the microstructure of the perovskite layer. In a theoretical study, Motta et al found that the exciton binding energy can vary depending on the degree of disorder in the material, concluding that the excitonic properties of MAPbI 3 largely depend on the electronic structure of the PbI 3 inorganic lattice.…”

Section: Absorptionmentioning

confidence: 99%

Impact of Structural Dynamics on the Optical Properties of Methylammonium Lead Iodide Perovskites

Panzer

Meier

et al. 2017

Advanced Energy Materials

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structure, [2] and changing the ratio of precursor compounds prior to the formation of the perovskite layer. [3] These approaches are based on modifying the crystallization process, for example, by controlling the composition of the precursor solution and by varying processing parameters. Such changes also led to major improvements in perovskite-based light-emitting devices within the last year. Initially, the current efficiencies were improved by optimizing the grain size to values below 100 nm, and by changing the precursor compound molar proportions. [4] More recently, efficient perovskite-based LEDs with external quantum efficiencies exceeding 10% were even obtained by expanding towards lower dimensional perovskite structures. [5] Different structures and dimensionalities resulted in altered charge-carrier dynamics affecting the radiative recombination efficiency. [5,6] By drawing strong correlations between structural properties and their electronic structure, major breakthroughs toward light-emitting devices or in photovoltaics could be achieved in very recent years. To a certain extent, this resembles the evolution in the field of organic semiconductors, where improved understanding of the interplay between morphological and electronic structure proved essential to facilitate the recent progress in organic photovoltaics, and the successful commercialisation of organic LED devices. Also, for hybrid perovskites the question of how crystal structure, shape, and grain size governs the electronic structure will remain an important topic in the future to further improve perovskite-based optoelectronic devices. Since the solution processability of hybrid perovskites enables easy tuning of material compositions, a large number of different hybrid perovskites were reported. For example, exchanging the organic cation can alter the crystal structure, shift phase transitions, as does formamidinium, or change further excited-state dynamics, as is happening with Cs or Ru. Furthermore, different halide anions change the optical and excited state properties. The optical bandgap can be changed from the UV to NIR region by replacing the halide from Cl to Br to I. Mixed-halide systems thereof even provide a way to gradually tune the respective bandgap. In fact, the recently reported, most stable and efficient perovskite solar cells (PSCs) are based on a highly optimized mixture of different anions and cations. [1,7] Nevertheless, the most investigated hybrid perovskite representative is the methylammonium lead iodide perovskite CH 3 NH 3 PbI 3 (MAPbI 3 ), which, in the meantime, has become Organolead halide perovskites have attracted a lot of attention over the recent years mostly due to their bright prospective application in photovoltaic devices. For further development, characterization of their physical properties plays a seminal role in order to gain an in-depth understanding of these mid-bandgap ionic semiconductors. Their unique optical and electronic properties are a result of their characteristic electronic stru...

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Absorption F-Sum Rule for the Exciton Binding Energy in Methylammonium Lead Halide Perovskites

Cited by 153 publications

References 37 publications

Breathing bands due to molecular order in CH3NH3PbI3

Breathing bands due to molecular order in CH3NH3PbI3

Discerning the Surface and Bulk Recombination Kinetics of Organic–Inorganic Halide Perovskite Single Crystals

Impact of Structural Dynamics on the Optical Properties of Methylammonium Lead Iodide Perovskites

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