Exciton Features in 0-, 2-, and 3-Dimensional Networks of [PbI<sub>6</sub>]<sup>4-</sup>Octahedra

Hirasawa, Masahiro; Ishihara, Teruya; Goto, T.

doi:10.1143/jpsj.63.3870

Cited by 154 publications

(160 citation statements)

References 11 publications

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“…31 The pale yellow color of macroscopic MAPI hydrate needles reported previously may originate from defects, disorder or impurities, for example traces of elemental iodine which can evolve in the mother liquor from oxidation of concentrated HI solutions, or from We reiterate that the MAPI film hydration process did not initially lead to the formation of a substantial amount of crystalline lead iodide. We speculate that the mechanism of irreversible decomposition of MAPI into HI, PbI 2 and CH 3 NH 2 can only happen in the presence of excess or liquid water which can dissolve the methylammonium ions.…”

Section: Figure 3bmentioning

confidence: 72%

Reversible Hydration of CH₃NH₃PbI₃ in Films, Single Crystals, and Solar Cells

et al. 2015

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Solar cells comprising methylammonium lead iodide perovskite (MAPI) are notorious for their sensitivity to moisture. We show that hydrated crystal phases are formed when MAPI is exposed to water vapour at room temperature and that these phase changes are fully reversed when the material is subsequently dried. The reversible formation of CH 3 NH 3 PbI 3 •H 2 O followed by (CH 3 NH 3 ) 4 PbI 6 •2H 2 O (upon long exposure times) was observed using time resolved XRD and ellipsometry of thin films prepared using 'solvent engineering', single crystals, and state of the art solar cells. In contrast to water vapour, the presence of liquid water results in the irreversible decomposition of MAPI to form PbI 2 . MAPI changes from dark brown to transparent on hydration; the precise optical constants of CH 3 NH 3 PbI 3 •H 2 O formed on single crystals were determined, with a bandgap at 3.1 eV. Using the single crystal optical constants and thin film ellipsometry measurements, the time dependent changes to MAPI films exposed to moisture were modelled. The results suggest that the mono-hydrate phase forms independently of the depth in the film suggesting rapid transport of water molecules along grain boundaries. Vapour phase hydration of an unencapsulated solar cell (initially J sc ≈ 19 mA cm -2 and V oc ≈ 1.05 V at 1 sun) resulted in more than a 90 % drop in short circuit photocurrent and around 200 mV loss in open circuit potential, but these losses were fully reversed after the cell was exposed to dry nitrogen for 6 hours. Hysteresis in the current-voltage characteristics was significantly increased after this dehydration, which may be related to changes in the defect density and morphology of MAPI following recrystallization from the hydrate. Based on our observations we suggest that irreversible decomposition of MAPI in the presence of water vapour only occurs significantly once a grain has been fully converted to the hydrate phase.

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Section: Figure 3bmentioning

confidence: 72%

Reversible Hydration of CH₃NH₃PbI₃ in Films, Single Crystals, and Solar Cells

et al. 2015

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“…The optical analysis presented above suggests the presence of an excitonic transition, probably very close to the continuum. Indeed, the presence of a Wannier-Mott exciton with a binding energy of about 45 meV has been predicted in the single crystal of CH 3 NH 3 PbI 3 at low temperatures 17,18 . Temperature-dependent, time-resolved photoluminescence (PL) is one approach for estimating the exciton binding energy in a semiconductor.…”

Section: Resultsmentioning

confidence: 96%

Excitons versus free charges in organo-lead tri-halide perovskites

et al. 2014

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Excitonic solar cells, within which bound electron-hole pairs have a central role in energy harvesting, have represented a hot field of research over the last two decades due to the compelling prospect of low-cost solar energy. However, in such cells, exciton dissociation and charge collection occur with significant losses in energy, essentially due to poor charge screening. Organic-inorganic perovskites show promise for overcoming such limitations. Here, we use optical spectroscopy to estimate the exciton binding energy in the mixed-halide crystal to be in the range of 50 meV. We show that such a value is consistent with almost full ionization of the exciton population under photovoltaic cell operating conditions. However, increasing the total photoexcitation density, excitonic species become dominant, widening the perspective of this material for a host of optoelectronic applications.

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“…Squares and triangles represent those for the PL bands which appear at lower energies beside the predominant PL band, as seen at P ¼ 4.5-6.5 GPa in Fig. 2 formed for 2D lead-iodide perovskites [10,11]. However, the electronic band structure does not seem to be fully understood yet.…”

Section: Resultsmentioning

confidence: 99%