Semiconductor Optics

Klingshirn, C.

doi:10.1007/978-3-642-28362-8

Cited by 360 publications

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“…It is reported that ¦ LT and the exciton binding energy of the two-dimensional perovskite lead bromide material (C 4 H 9 NH 3 ) 2 PbBr 4 are about 70 meV and 390 480 meV, 22,23 respectively. Considering the relation among ¦ LT , the oscillator strength, and the exciton binding energy, 24,25 we can roughly estimate the exciton binding energy of CH 3 NH 3 -PbBr 3 at low temperature to be 80100 meV, which is almost in accordance with the reported value of 76 meV.…”

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Excitonic Feature in Hybrid Perovskite CH3NH3PbBr3 Single Crystals

et al. 2015

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We have measured the temperature dependence of the reflection and photoluminescence spectra of a lead bromide hybrid material (CH 3 NH 3 PbBr 3 ) using high-quality macroscopic single crystals. Single crystals provide clear and sampleindependent reflection spectra that permit discussion of the properties of the photoexcited carriers. We have found that excitons still exist in CH 3 NH 3 PbBr 3 , even at room temperature. We have also determined the temperature dependence of the exciton resonance energy and the line width.In recent years, lead halide organicinorganic hybrid perovskite materials have attracted considerable attention for photovoltaic applications. 16 The reported power conversion efficiencies (PCE) of the hybrid perovskite-type solar cells with lead iodide materials (CH 3 NH 3 PbI 3¹x Cl x ) are more than 20%. Meanwhile, such materials have been studied from the viewpoint that they form ideal low-dimensional systems and have stable excitons. 812 Even in three-dimensional hybrid materials, the exciton binding energies were reported to be 3750 meV. 13This suggests that stable excitons might exist even at room temperature, and seems to contradict the fact that these materials function as excellent photovoltaic materials, for which dissociation of photoexcited electronhole pairs is necessary to extract the photocurrent.While most studies of the excitonic properties have been performed at low temperatures, solar cells work at room temperature. Therefore, in order to resolve the contradiction stated above, it is important to study the temperature dependence of photoexcited carrier properties in these materials. Recent studies of CH 3 NH 3 PbI 3 indicate that the static dielectric constant shows a rapid increase with increasing temperature, suggesting that this effectively decreases the exciton binding energy. 14,15 Consequently, these results support the view that the excitons dissociate at room temperature in CH 3 NH 3 PbI 3 . In order to clarify the intrinsic properties of these materials, however, such investigations should be performed with high-quality single crystals, which are less affected by defects or impurities. Nevertheless, there are few studies on hybrid perovskite single crystals. 1618In this work, we used high-quality macroscopic single crystals of lead bromide hybrid material (CH 3 NH 3 PbBr 3 ), which has similar properties to CH 3 NH 3 PbI 3 but has a larger band gap (ca. 2.35 eV at room temperature).13 Although CH 3 NH 3 PbBr 3 does not absorb near infrared light, a PCE of more than 10% was reported. 19 The reason why we chose CH 3 NH 3 PbBr 3 is that macroscopic single crystals are more easily synthesized than those of CH 3 NH 3 PbI 3 . Using the single crystals, we have measured the temperature dependence of the reflection and photoluminescence (PL) spectra to discuss the properties of the photoexcited carriers. Our results indicate that excitons still exist in CH 3 NH 3 PbBr 3 , even at room temperature. In addition, we have determined the temperature dependence of the exciton reso...

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confidence: 85%

“…Supposing that the inhomogeneous broadening is small enough, this phenomenon can be explained as being due to excitonphonon interactions. describing the coupling between the exciton and the LO phonon, 25 the line width is expressed as…”

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confidence: 99%

Excitonic Feature in Hybrid Perovskite CH3NH3PbBr3 Single Crystals

et al. 2015

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“…3(b). X and Xshow a rather linear behavior indicated by the orange solid line, as expected for an excitonic feature [18]. In contrast, the L 1 /XX peak exhibits a linear dependence at low excitation density, while for excitation densities larger than 25 kWcm -2 , the data is well-described by a quadratic fit, indicated by the green solid line in Fig.…”

Section: Resultsmentioning

confidence: 60%

“…These have been attributed to surface-adsorbate-bound excitons in MoS 2 [15] and to crystal-defect-bound exciton states in single-layer diselenides [16,17]. Given the large binding energy of the excitons, the formation of molecular states consisting of two excitons, so-called biexcitons [18], is to be expected in dichalcogenide single-layers. Biexciton PL emission should be at energies below the exciton emission due to the additional binding energy, in a similar energy range as defect-bound exciton emission.…”

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confidence: 99%

Identification of excitons, trions and biexcitons in single-layer WS₂

Plechinger

Nagler

Kraus

et al. 2015

Phys. Status Solidi RRL

323

393

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Single-layer WS$_2$ is a direct-gap semiconductor showing strong excitonic photoluminescence features in the visible spectral range. Here, we present temperature-dependent photoluminescence measurements on mechanically exfoliated single-layer WS$_2$, revealing the existence of neutral and charged excitons at low temperatures as well as at room temperature. By applying a gate voltage, we can electrically control the ratio of excitons and trions and assert a residual n-type doping of our samples. At high excitation densities and low temperatures, an additional peak at energies below the trion dominates the photoluminescence, which we identify as biexciton emission.Comment: 6 pages, 5 figure

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“…The latter consists of an air/(underlaying film) composite and its optical constants were calculated according to Bruggeman's approximation. [26,20] In the case of the opaque samples S1 and S2, the optical properties can be modeled by a Lorentz and a Tauc-Lorentz oscillators [27] as follows: the optical properties of S1 can be represented by a Lorentz oscillator exhibiting a broad absorption along the spectrum (amplitude Amp 14.0 AE 1.0, position E n 0.57 AE 0.04 eV, and width Br 6.1 AE 0.8 eV). This Lorentz oscillator describes the absorption caused by presence of electrons in the conduction band.…”

Section: Optical Propertiesmentioning

confidence: 99%

Spectroscopic Ellipsometry and Microstructure Characterization of Photochromic Oxygen‐Containing Yttrium Hydride Thin Films

Montero

Karazhanov

2018

Physica Status Solidi (a)

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Oxygen‐containing yttrium hydride, YHx:Oy, is an inorganic phothochromic material which exhibits promising features for its application in smart windows, ophthalmic lenses, and many more. In the present work the optical properties of photochromic and non‐photochromic YHx:Oy thin films prepared by magnetron sputtering are studied by variable angle ellipsometry and spectrophotometry. These include the study of the complex refractive index, the transmittance, and luminous transmittance, as well as the reflectance of a selection of samples of diverse structural properties obtained under different deposition conditions. In the case of the photochromic YHx:Oy thin films, the refractive index in the near infrared and visible regions is found similar to the one corresponding to yttrium oxide, Y2O3. However, the YHx:Oy films exhibit a smaller band gap and hence higher absorption in the near ultraviolet than Y2O3. The photodarkening potential of the films are also quantified and characterized by the study and modeling of their optical properties before and after illumination. Our results show that photochromic YHx:Oy films, with a luminous transmittance above 80 % in the clear state, can reduce its transparency up to a 30% after 1 h illumination at 1 Sun.

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Semiconductor Optics

Cited by 360 publications

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Excitonic Feature in Hybrid Perovskite CH3NH3PbBr3 Single Crystals

Excitonic Feature in Hybrid Perovskite CH3NH3PbBr3 Single Crystals

Identification of excitons, trions and biexcitons in single-layer WS₂

Spectroscopic Ellipsometry and Microstructure Characterization of Photochromic Oxygen‐Containing Yttrium Hydride Thin Films

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Semiconductor Optics

Cited by 360 publications

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Excitonic Feature in Hybrid Perovskite CH3NH3PbBr3 Single Crystals

Excitonic Feature in Hybrid Perovskite CH3NH3PbBr3 Single Crystals

Identification of excitons, trions and biexcitons in single-layer WS2

Spectroscopic Ellipsometry and Microstructure Characterization of Photochromic Oxygen‐Containing Yttrium Hydride Thin Films

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Identification of excitons, trions and biexcitons in single-layer WS₂