Spatial Localization of Excitons and Charge Carriers in Hybrid Perovskite Thin Films

Simpson, Mary Jane; Doughty, Benjamin; Yang, Bin; Xiao, Kai; Zhao, Ying

doi:10.1021/acs.jpclett.5b01050

Cited by 59 publications

(75 citation statements)

References 40 publications

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“…Diffraction peaks of MAPbBr 3 at 14.79° for (100) plane, 30.06° for (200) plane, 45.85° for (300) plane, reveal the characteristics of the perovskite square phase according to the previous work . The linear absorption spectrum is shown in Figure f, a sharp peak at 2.35 eV can be ascribed to the excitonic absorption, the spectrum is then simulated by Elliott's formula, where the linear absorption can be described by the continuum and excitonic states' absorption. Two‐photon absorption coefficient was calculated from pump–probe differential transmission spectra (Figure S2, Supporting Information).…”

Section: Resultsmentioning

confidence: 56%

“…Unlike the confirmed excitonic emission in MAPbBr 3 NCs, due to the extremely large exciton binding energy (≈375 meV), it is a bit misty to understand the light emission origin in 3D MAPbBr 3 due to this wide spread of reported exciton binding energies. Considering the thermal energy at room temperature ( k B T ≈ 26 meV), excitons and free carriers could coexist in this 3D MAPbBr 3 perovskite . Excitons conform to the Bose–Einstein statistics, while free carriers follow the Fermi–Dirac statistics.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Two‐Photon Optical Properties in Individual Organic–Inorganic Perovskite Microplates

Wei

et al. 2017

Advanced Optical Materials

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yield [15][16][17] make these metal-halide perovskites also promising for applications in light emitting diodes (LEDs) and lasers. [18][19][20][21][22][23] Specifically speaking, amplified spontaneous emission (ASE) has been demonstrated in metal-halide perovskite thin films. Multiphoton pumped upconverted photoluminescence (PL) and coherent light emission have been achieved with perovskite single crystals and nanocrystals (NCs). [24][25][26][27][28][29][30][31][32][33][34] Metal-halide perovskite lasing has been demonstrated with various microcavity structures. [35][36][37][38] For use as coherent light source, the lasing threshold obtained is also highly dependent on the optical cavity, which is formed by the close loop light reflection from the nanostructure surfaces that becomes a standing wave cavity resonator. The regular shape of the perovskite microstructures with various sizes differs in various optical confinement abilities, which suggests that lasing in perovskite microstructures possesses size-dependent behavior. [39][40][41][42] Hence, a clearer understanding of the size-dependent coherent light emission behavior is crucial for developing metal-halide perovskite on chip nanolasers. Furthermore, the photogenerated species (especially in CH 3 NH 3 PbBr 3 (MAPbBr 3 )) and their contribution to the lasing performance in these perovskites have not been fully revealed. [43] The exciton binding energy in 3D MAPbBr 3 has been estimated with various techniques. However, the reported values are highly controversial and covered a wide range from 25 to 150 meV. [44][45][46][47][48] Unlike the confirmed excitonic emission in MAPbBr 3 NCs, due to the extremely large exciton binding energy (≈375 meV), [49] it Metal-halide perovskites are recently extensively investigated as light absorbing material in solar cells. The outstanding optoelectronic properties and tunable light emission of the perovskites also make them promising candidates for light emitting diodes and lasers. However, understanding the relevant mechanisms and processes of the dependence of perovskite light emission on temperature and crystal size is still challenging. Herein, the CH 3 NH 3 PbBr 3 monocrystals of different sizes are uniformly excited by two-photon absorption at 800 nm (100 fs, 1 KHz). In contrast to the reported relative large exciton binding energy (≈76 meV) and spectrum clearly resolved excitonic absorption, the light emission origin in CH 3 NH 3 PbBr 3 microcrystals at room temperature is unambiguously determined to be dominated by free electron-hole bimolecular recombination. The coherent light emission threshold of CH 3 NH 3 PbBr 3 microcrystal increases with temperature, which is closely related to the temperature induced transition from exciton gas to free charge carriers. In addition, the coherent light emission threshold is found to decrease with the microcrystal size, which could be well interpreted by the interaction between the optical confinement, defect density, and cavity quantum electrodynamics effect. These results pre...

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Section: Resultsmentioning

confidence: 56%

Section: Introductionmentioning

confidence: 99%

Two‐Photon Optical Properties in Individual Organic–Inorganic Perovskite Microplates

Wei

et al. 2017

Advanced Optical Materials

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“…[44,45] Besides the phenomenon of lightinduced halide migration discussed above, films synthesized from Cl-containing precursors typically contain a tiny amount of residual chlorine dopants (m < 0.12 in MAPbI 3−m Cl m ). [44,45] Besides the phenomenon of lightinduced halide migration discussed above, films synthesized from Cl-containing precursors typically contain a tiny amount of residual chlorine dopants (m < 0.12 in MAPbI 3−m Cl m ).…”

Section: Resultsmentioning

confidence: 99%

How Methylammonium Cations and Chlorine Dopants Heal Defects in Lead Iodide Perovskites

Nan

Zhang

Abdi‐Jalebi

et al. 2018

Advanced Energy Materials

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Lead tri‐iodide methylammonium (MAPbI3) perovskite polycrystalline materials show complex optoelectronic behavior, largely because their 3D semiconducting inorganic framework is strongly perturbed by the organic cations and ubiquitous structural or chemical inhomogeneities. Here, a newly developed time‐dependent density functional theory‐based theoretical formalism is taken advantage of. It treats electron–hole and electron–nuclei interactions on the same footing to assess the many‐body excited states of MAPbI3 perovskites in their pristine state and in the presence of point chemical defects. It is shown that lead and iodine vacancies yield deep trap states that can be healed by dynamic effects, namely rotation of the methylammonium cations in response to point charges, or through slight changes in chemical composition, namely by introducing a tiny amount of chlorine dopants in the defective MAPbI3. The theoretical results are supported by photoluminescence experiments on MAPbI3−mClm and pave the way toward the design of defect‐free perovskite materials with optoelectronic performance approaching the theoretical limits.

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“…The task has been pursued using an array of time‐resolved optical spectroscopy techniques. Many reports investigated the photoexcitation dynamics by differential femtosecond transmission or reflection spectroscopy . This technique detects small changes in the linear absorption/reflection spectrum near the optical gap induced by a population of photoexcitations, but it is not very selective to the nature of photoexcitations.…”

Section: Introductionmentioning

confidence: 99%

Perovskite Excitonics: Primary Exciton Creation and Crossover from Free Carriers to a Secondary Exciton Phase

Sarritzu

Sestu

Marongiu

et al. 2017

Advanced Optical Materials

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opposite charges toward opposite electrodes. On the other hand, light-emitting diodes (LEDs) require high rates of radiative recombination at low injection levels, in order to operate efficiently. This condition is best satisfied if the emitting species are excitons, as their radiative recombination rate is proportional to the exciton density. Conversely, light emission from free charges is quite inefficient at low carrier concentrations, since radiative decay is a second order process in the carrier density. Understanding exciton formation processes is therefore of importance to design perovskite materials that bolster light emission.However, exciton formation in hybrid perovskites has been elusive so far. The mass-action law, known as Saha equation, [12] foresees an equilibrium with predominance of free carriers for excited state densities relevant to devices, despite the fact that the measured exciton binding energy is larger than the ambient thermal energy, as for CH 3 NH 3 PbBr 3 (E b = 60 meV). [13] Saha equation also predicts the formation of a majority population of excitons at large excitation densities, but such crossover has not been observed yet, hinting that thermodynamic equilibrium between bound and unbound states may not be assumed. In order to identify the exciton formation processes, the determination of the photoexcitation kinetics becomes the central issue. The task has been pursued using an array of time-resolved optical spectroscopy techniques. Many reports investigated the photoexcitation dynamics by differential femtosecond transmission or reflection spectroscopy. [5,[14][15][16][17][18][19][20][21][22][23][24] This technique detects small changes in the linear absorption/reflection spectrum near the optical gap induced by a population of photoexcitations, but it is not very selective to the nature of photoexcitations. Terahertz (THz) pump-probe spectroscopy overcomes this limitation and directly measures the absorption spectrum due the internal quantum transitions of the exciton population (1s→2p,3p, and so on) and free electronhole plasma. In hybrid perovskites, the THz absorption spectrum also contains interfering contributions from phonon modes. Most experiments reported to date agree that free carriers are the only photoexcitations in hybrid perovskites; [3,[25][26][27] however, two recent studies suggest that transitions between excitonic Rydberg states are also observed in CH 3 NH 3 PbI 3 ; yet, the ensuing estimates of Understanding exciton formation is of fundamental importance for emerging optoelectronic materials, like hybrid organic-inorganic perovskites, as excitons are the lowest-energy photoexcitations in semiconductors, are electrically neutral, and do not directly contribute to charge transport, but can emit light more efficiently than free carriers. However, despite the increasing attention toward these materials, experimental results on the processes of formation of an exciton population in perovskites are still elusive. Here, an ultrafast differential photoluminescence ...

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Spatial Localization of Excitons and Charge Carriers in Hybrid Perovskite Thin Films

Cited by 59 publications

References 40 publications

Two‐Photon Optical Properties in Individual Organic–Inorganic Perovskite Microplates

Two‐Photon Optical Properties in Individual Organic–Inorganic Perovskite Microplates

How Methylammonium Cations and Chlorine Dopants Heal Defects in Lead Iodide Perovskites

Perovskite Excitonics: Primary Exciton Creation and Crossover from Free Carriers to a Secondary Exciton Phase

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