Density-dependent dynamical coexistence of excitons and free carriers in the organolead perovskite 
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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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“…3 (b). We ascribe the fourthpower dependence (quadratic in excitation density) to free carrier recombination [57]. As shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

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

et al. 2017

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“…Therefore, if the variation on photoproducts is found, it would represent significant change in morphology. Based on this idea, the relationship between photoexcited exciton and free carriers was analyzed by our recently developed density-resolved spectroscopic method [88]. The method focuses on the excitation density-dependent photoproduct system, since the correlation of exciton and free carriers in semiconductors is density-dependent.…”

Section: Optical Methods To Observe the Broad Existence Of Subgrain Twmentioning

confidence: 99%

“…The method focuses on the excitation density-dependent photoproduct system, since the correlation of exciton and free carriers in semiconductors is density-dependent. According to the Saha-Langmuir equation [89] and fixed fluorescence intensity I(n) [88]:…”

Section: Optical Methods To Observe the Broad Existence Of Subgrain Twmentioning

confidence: 99%

Twin Domains in Organometallic Halide Perovskite Thin-Films

Liu

et al. 2018

Crystals

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The perovskite is a class of material with crystalline structure similar to CaTiO 3. In recent years, the organic-inorganic hybrid metallic halide perovskite has been widely investigated as a promising material for a new generation photovoltaic device, whose power conversion efficiency (PCE) record reaches 22.7%. One of its underlying morphological characteristics is the twin domain within those sub-micron sized crystal grains in perovskite thin films. This is important for discussion since it could be the key for understanding the fundamental mechanism of the device's high performance, such as long diffusion distance and low recombination rate. This review aims to summarize studies on twin domains in perovskite thin films, in order to figure out its importance, guide the current studies on mechanism, and design new devices. Firstly, we introduce the research history and characteristics of widely known twin domains in inorganic perovskite BaTiO 3. We then focus on the impact of the domain structure emerging in hybrid metallic halide perovskite thin films, including the observation and discussion on ferroelectricity/ferroelasity. The theoretical analysis is also presented in this review. Finally, we present a spectroscopic method, which can reveal the generality of twin domains within perovskite thin films. We anticipate that this summary on the structural and physical properties of organometallic halide perovskite will help to understand and improve the high-performance of photovoltaic devices.

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“…This behavior is characteristic of the Burstein-Moss shift due to band filling with free carriers upon photo-excitation at increasing carrier densities. 29,30,31,32,33 Figure 2(b)…”

Section: Toc Graphicsmentioning

confidence: 99%

“…d) shows the ratio of the squared free-carrier population over the population of excitons. The Saha equation, correlating this ratio of free carriers and excitons to the excitation density in hot electronhole plasma, was used to model the obtained data:29,5,44,50 …”

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confidence: 99%

Origin of the Enhanced Photoluminescence Quantum Yield in MAPbBr₃ Perovskite with Reduced Crystal Size

et al. 2018

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Methylammonium lead bromide perovskite (MAPbBr3) has been widely investigated for applications in visible perovskite light-emitting diodes (LEDs). Fine-tuning of the morphology and of the crystal size, from the microscale down to the quantum confinement regime, has been used to increase the photoluminescence quantum yield (PLQY). However, the physical processes underlying the PL emission of this perovskite remain unclear. Here, we elucidate the origin of the PL emission of polycrystalline MAPbBr3 thin films by different spectroscopic techniques. We estimate the exciton binding energy, the reduced exciton effective mass, and the trap density. Moreover, we confirm the coexistence of free carriers and excitons, quantifying their relative population and mutual interaction over a broad range of excitation densities. Finally, the enhanced PLQY upon crystal size reduction to the micro- and nanometer scale in the presence of additives is attributed to favored excitonic recombination together with reduced surface trapping thanks to efficient passivation by the additives.

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Density-dependent dynamical coexistence of excitons and free carriers in the organolead perovskite CH3NH3PbI

Cited by 29 publications

References 40 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

Twin Domains in Organometallic Halide Perovskite Thin-Films

Origin of the Enhanced Photoluminescence Quantum Yield in MAPbBr₃ Perovskite with Reduced Crystal Size

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Density-dependent dynamical coexistence of excitons and free carriers in the organolead perovskite CH3NH3PbI

Cited by 29 publications

References 40 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

Twin Domains in Organometallic Halide Perovskite Thin-Films

Origin of the Enhanced Photoluminescence Quantum Yield in MAPbBr3 Perovskite with Reduced Crystal Size

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Origin of the Enhanced Photoluminescence Quantum Yield in MAPbBr₃ Perovskite with Reduced Crystal Size