Indirect to direct bandgap transition in methylammonium lead halide perovskite

Wang, Tianyi; Daiber, Benjamin; Frost, Jarvist M.; Mann, Sander A.; Garnett, Erik C.; Walsh, Aron; Ehrler, Bruno

doi:10.1039/c6ee03474h

Cited by 346 publications

(353 citation statements)

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“…The coexistence of a direct and an indirect band gap has also been observed in (CH 3 NH 3 )PbI 3 , with energetic spacings of 47 meV [49] and 60 meV [50]. The observation of direct and indirect gaps for both (CH 3 NH 3 )PbI 3 and (CH 3 NH 3 )PbBr 3 indicates that they might be a common property of both OIPS, originating from their sim-ilar band structures [88].…”

Section: F Discussion Of the Two Observed Transitionsmentioning

confidence: 75%

“…56. As Rashba splitting has been observed experimentally for (CH 3 NH 3 )PbBr 3 [53] and proposed as the origin of an indirect gap in (CH 3 NH 3 )PbI 3 [50], the coexistence of direct and indirect transitions poses another possible explanation for the measured spectra.…”

Section: F Discussion Of the Two Observed Transitionsmentioning

confidence: 96%

“…Highenergy carriers have not been apparent to the same degree in earlier studies on thin films. Along another line of research, studies on (CH 3 NH 3 )PbI 3 thin films reveal the coexistence of a direct and an indirect optical band gap with measured energetic spacings of 47 meV [49] and 60 meV [50]. A slightly indirect band gap has been proposed as one of the origins of the low carrier recombination rate found in OIPS [12,14,15].…”

Section: Introductionmentioning

confidence: 99%

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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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Section: F Discussion Of the Two Observed Transitionsmentioning

confidence: 75%

Section: F Discussion Of the Two Observed Transitionsmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

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

et al. 2017

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“…Such questions need to be asked to develop a clear understanding about how the various complex morphological aspects of hybrid perovskites correspond to their optical response. Moreover, the existence of an indirect bandgap slightly below the direct bandgap of MAPbI 3 was reported recently, originating from Rashba splitting of the conduction band due to polar distortions of the PbI 6 cage induced through pressure, [46] strain, or electrical fields, [47] which also influence the optical properties. [48] Where theoretical calculations seem clear, [47,49] some previous studies present different interpretations of similar experimental data, [50] or find different trends of parameters.…”

Section: Photoluminescencementioning

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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“…[25] Importantly, just like the bulk sample, no real PL response from 200 QL or thicker flakes was observed. Therefore, quantum confinement effects are www.advopticalmat.de dominated by a strain-induced second-order bandgap transitions from direct to indirect, [51,52] which is evident by the redshift and significant PL quenching for <10 QLs. The phenomenon is consistent with effective mass approximation (EMA), which describes remarkable enhancement in the PL response from quantum-size nanomaterials owing to the quantum confinement effect.…”

Section: Wwwadvopticalmatdementioning

confidence: 99%

Ultrahigh Room‐Temperature Photoluminescence from Few to Single Quintuple Layer Bi₂Te₃ Nanosheets

Hussain

Zhang

Lang

et al. 2018

Advanced Optical Materials

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photoluminescence is considered as one of the primary figures of merit for a 2D semiconductor to be a promising material for nano-optoelectronic, [10,11] sensing, [12,13] and photodetector applications. [14,15] Therefore, it remains challenging to achieve substantial room-temperature photoluminescence response from Bi 2 Te 3 nanocrystals. Additionally, surface plasmon resonance (SPR) defines collective oscillations of conduction electrons and has been attracting highly devoted research interest owing to its promising applications in on-chip subwavelength electro-optical devices, [16][17][18] sensing, [19,20] and energy harvesting. [15,[20][21][22] Due to limited plasmonic materials and modulation methods, effective control over the energy modes and intensities of surface plasmon resonances in the visible region remains challenging.The effective mass approximation (EMA) model describes the opening of bandgaps in ultrathin nanostructures, due to quantum confinement effects. [23] Therefore, dimensionally restricted 2D nanocrystals of Bi 2 Te 3 might provide an opportunity to achieve remarkably enhanced PL properties through the bandgap opening/transition and potentially hold SPR. In recent past, 2D nanocrystals of Bi 2 Te 3 have been reported to support surface plasmons and exhibit PL responses. For instance, visible SPR from 2D Bi 2 Te 3 nanoplates by cathodoluminescence [24] and tunablity of visible SPR modes by Se doping in Bi 2 Te 3 [25] have been demonstrated using PL spectroscopy. Meanwhile, PL spectroscopy, in particular, offers a great opportunity to study quantum confinement-induced exciting phenomena originating from light-matter interactions at the nanoscale. The size-dependent characteristics and physical Owing to its narrow indirect bandgap, bulk bismuth telluride (Bi 2 Te 3 ) exhibits exceptionally low room-temperature photoluminescence (PL). Consequently, it remains challenging to achieve promising optical and optoelectronic performance from Bi 2 Te 3 . Moreover, due to the lack of plasmonic materials and available modulation methods, it is challenging to effectively control the surface plasmon resonance intensities in the visible region. Herein, thickness-dependent photoluminescence studies unveil ultrahigh (282-fold) room-temperature photoluminescence (visible) from 20 quintuple layer Bi 2 Te 3 nanosheets (NSs) compared to 200 quintuple layer NSs, attributable to a significant bandgap opening. Intriguingly, considerable photoluminescence quenching is observed beyond the thickness of 20 quintuple layer Bi 2 Te 3 . The PL emission is further optimized with reference to the number of quintuple layers, and the mechanism possibly responsible for such PL behavior is elucidated. Moreover, the thickness modulation is put forward as an effective strategy to control visible surface plasmon resonance energy modes and their intensities. Bi 2 Te 3 nanosheets with large area and high crystallinity are fabricated on various silicon substrates by a facile hot-pressing strategy, which facilitates investigation of in...

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Indirect to direct bandgap transition in methylammonium lead halide perovskite

Cited by 346 publications

References 50 publications

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

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

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

Ultrahigh Room‐Temperature Photoluminescence from Few to Single Quintuple Layer Bi₂Te₃ Nanosheets

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Indirect to direct bandgap transition in methylammonium lead halide perovskite

Cited by 346 publications

References 50 publications

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

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

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

Ultrahigh Room‐Temperature Photoluminescence from Few to Single Quintuple Layer Bi2Te3 Nanosheets

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Ultrahigh Room‐Temperature Photoluminescence from Few to Single Quintuple Layer Bi₂Te₃ Nanosheets