Giant Bandgap Renormalization and Exciton–Phonon Scattering in Perovskite Nanocrystals

Saran, Rinku; Heuer‐Jungemann, Amelie; Kanaras, Antonios G.; Curry, Richard J.

doi:10.1002/adom.201700231

Cited by 155 publications

(190 citation statements)

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“…The explanation for this anomalous trend is currently under discussion. While Saran et al, for example, use a Bose–Einstein two‐oscillator model to explain this behavior, Kontos et al invoke the off‐centering (emphanisis) of the metal ions in the MeI 6 octahedra as well as additional dynamic symmetry breaking to explain this trend.…”

Section: Resultsmentioning

confidence: 99%

Cooling, Scattering, and Recombination—The Role of the Material Quality for the Physics of Tin Halide Perovskites

Kahmann

Shao

Loi

2019

Adv Funct Materials

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Tin-based perovskites have long remained a side topic in current perovskite optoelectronic research. With the recent efficiency improvement in thin film solar cells and the observation of a long hot carrier cooling time in formamidinium tin iodide (FASnI 3 ), a thorough understanding of the material's photophysics becomes a pressing matter. Since pronounced background doping can easily obscure the actual material properties, it is of paramount importance to understand how different processing conditions affect the observed behavior. Using photoluminescence spectroscopy, thin films of FASnI 3 fabricated through different protocols are therefore investigated. It is shown that hot carrier relaxation occurs much faster in highly p-doped films due to carrier-carrier scattering. From high quality thin films, the longitudinal optical phonon energy and the electron-phonon coupling constant are extracted, which are fundamental to understanding carrier cooling. Importantly, high quality films allow for the observation of a previously unreported state of microsecond lifetime at lower energy in FASnI 3 , that has important consequences for the discussion of long lived emission in the field of metal halide perovskites.

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Section: Resultsmentioning

confidence: 99%

Cooling, Scattering, and Recombination—The Role of the Material Quality for the Physics of Tin Halide Perovskites

Kahmann

Shao

Loi

2019

Adv Funct Materials

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“…We remind that our predicted band gaps do not take into account the effects of band gap renormalization due to electron-phonon coupling in HOP, which has been shown to be non-negligible especially at high temperature [68][69][70] for LDA and ppTB-mBJ, respectively. For both compounds, a rather obvious qualitative difference between LDA and ppTB-mBJ is the width of the valence band maximum (VBM) and CBM that is smaller with ppTB-mBJ.…”

Section: A 3d Hop Compoundsmentioning

confidence: 91%

Efficient and accurate calculation of band gaps of halide perovskites with the Tran-Blaha modified Becke-Johnson potential

et al. 2019

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We report on a reoptimization of the Tran-Blaha modified Becke-Johnson (TB-mBJ) potential dedicated to the prediction of the band gaps of 3-dimensional (3D) and layered hybrid organicinorganic perovskites (HOP) within pseudopotential-based density functional theory methods. These materials hold promise for future photovoltaic and optoelectronic applications. We begin by determining a set of parameters for 3D HOP optimized over a large range of materials. Then we consider the case of layered HOP. We design an empirical relationship that facilitates the prediction of band gaps of layered HOP with arbitrary interlayer molecular spacers with a computational cost considerably lower than more advanced methods like hybrid functionals or GW. Our study also shows that substituting interlayer molecular chains of layered HOP with Cs atoms is an appealing and cost-effective route to band gap calculations. Finally, we discuss on the pitfalls and limitations of TB-mBJ for HOP, notably its tendency to overestimate the effective masses due to the narrowing of the band dispersions. We expect our results to extend the use of TB-mBJ for other low-dimensional materials. 2 B. Traore et coll. Phys. Rev.

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“…Exciton–phonon coupling has been studied in both hybrid and all‐inorganic perovskites, with most investigations focusing on the understanding of the temperature dependence of PL linewidth broadening by such coupling . For example, Phuong et al investigated the exciton–phonon coupling in MAPbI 3 single crystals at low temperatures (15–80 K) using both temperature‐dependent photocurrent (PC) and PL spectroscopy ( Figure a) .…”

Section: Excitons and Related Phenomena In Metal Halide Perovskitesmentioning

confidence: 99%

“…The temperature dependence of the PL exciton linewidth broadening arising from acoustic phonon interaction Γ ( T ) = Γ inh + Γ AC (violet dash–dot line), LO phonon interaction Γ ( T ) = Γ inh + Γ LO (yellow dash–dot line), inhomogeneous broadening term Γ ( T ) = Γ inh (horizontal gray dotted line) and due to the presence of impurities Γ ( T ) = Γ inh + Γ imp (only in the case of CsPbBr 3 nanocrystals, orange dash–dot line in (g)) is also shown in the respective figure for each nanocrystal type. c–h) Reproduced with permission . Copyright 2017, Wiley‐VCH.…”

Section: Excitons and Related Phenomena In Metal Halide Perovskitesmentioning

confidence: 99%

“…Wide excitonic linewidth broadening was also found in perovskite nanocrystals . Saran et al attributed the PL linewidth broadening in CsPbX 3 (X = I, Br, and Cl) nanocrystals to the strong exciton–phonon coupling which also induced a giant bandgap renormalization in the materials with redshift of the bandgap by decreasing temperature . The authors examined the exciton–phonon interactions in CsPbX 3 nanocrystals by the temperature‐dependent PL studies (Figure c–e).…”

Section: Excitons and Related Phenomena In Metal Halide Perovskitesmentioning

confidence: 99%

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Properties of Excitons and Photogenerated Charge Carriers in Metal Halide Perovskites

2019

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their great success in photovoltaics (PVs), with a phenomenally rapid rise of the power conversion efficiency (PCE) from 3.8% [1] to over 23% [2,3] in the past few years. Such high PCE of perovskite solar cells has been ascribed to the ultralong carrier lifetimes, [4][5][6][7][8] long carrier diffusion lengths, [9][10][11][12][13][14] and the extraordinarily defect tolerance. [15][16][17] Following the success of perovskites in photovoltaics, research on light-emitting diodes (LEDs), [18,19] amplified spontaneous emission (ASE) or lasers, [20][21][22][23][24] and photodetectors [25][26][27][28][29] have also gained substantial interests. Meanwhile, the rapid progress of MHPs on various applications spurred a flurry of photophysical studies in order to understand the origin of the high performance of these devices, of which the nature of the photoexcitation species has been mostly debated. [5,22,30,31] Since the photoexcitation states near the bandgap affect the key processes such as charge transport and light emission of optoelectronic devices, there is no doubt that the investigation of electronic excitations near the optical band edge is crucial for MHPs. Such knowledge is essential not only for understanding the correlation between the fundamental photophysics and device performances, but also offering a guideline for their further applications with improved performances. Generally, there are two kinds of photoexcitations near the band edge for direct bandgap semiconductors: free carriers and excitons. Exciton binding energy that reflects the Coulomb interaction strength between photoexcited electrons and holes determines the balance of the populations between the two species. Typically, inorganic semiconductors are free-carrier materials with the exciton binding energies only in few meV at room temperature and their excited states being populated principally by free carriers. While organic semiconductors are excitonic materials with the exciton binding energies in hundreds of meV and thus excitons prevailing in the excited states. Whereas, MHPs that combine some merits of organic and inorganic semiconductors seem to stand for an exotic class of semiconductors between these two limiting cases, with the experimentally determined exciton binding energy varying in a wide range of 2 to more than 50 meV for the prototype perovskite MAPbI 3 . [30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45][46][47][48] Such large variations of the exciton binding energies reported for MHPs give rise to a strongly debated question, that is, whether free carriers or excitons are generated upon photoexcitation? In other words, what is the nature of the photoexcitation species Metal halide perovskites (MHPs) have recently attracted great attention from the scientific community due to their excellent photovoltaic performance as well as their tremendous potential for other optoelectronic applications such as light-emitting diodes, lasers, and photodetectors. Despite the rapid progress in device applications, a solid unders...

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Giant Bandgap Renormalization and Exciton–Phonon Scattering in Perovskite Nanocrystals

Cited by 155 publications

References 57 publications

Cooling, Scattering, and Recombination—The Role of the Material Quality for the Physics of Tin Halide Perovskites

Cooling, Scattering, and Recombination—The Role of the Material Quality for the Physics of Tin Halide Perovskites

Efficient and accurate calculation of band gaps of halide perovskites with the Tran-Blaha modified Becke-Johnson potential

Properties of Excitons and Photogenerated Charge Carriers in Metal Halide Perovskites

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