Temperature dependent energy levels of methylammonium lead iodide perovskite

Foley, Benjamin J.; Marlowe, Daniel L.; Sun, Keye; Saidi, Wissam A.; Scudiero, Louis; Gupta, Mool C.; Choi, Joshua J.

doi:10.1063/1.4922804

Cited by 169 publications

(179 citation statements)

References 40 publications

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“…Note that, for the HEAT1 process, upon heating from 80 to 140 K, the ∼1.85-eV emission peak experiences a blue shift of 0.08 eV, which is typical behavior due to the positive temperature coefficient of bandgap in lead halide perovskites (24). However, at 160 K, the emission peak shifts back to 1.77 eV, and, upon further heating to 400 K, it experiences a blue shift of 0.14 eV.…”

Section: Significancementioning

confidence: 92%

Origin of long lifetime of band-edge charge carriers in organic–inorganic lead iodide perovskites

Chen

Foley

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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161

179

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Long carrier lifetime is what makes hybrid organic-inorganic perovskites high-performance photovoltaic materials. Several microscopic mechanisms behind the unusually long carrier lifetime have been proposed, such as formation of large polarons, Rashba effect, ferroelectric domains, and photon recycling. Here, we show that the screening of band-edge charge carriers by rotation of organic cation molecules can be a major contribution to the prolonged carrier lifetime. Our results reveal that the band-edge carrier lifetime increases when the system enters from a phase with lower rotational entropy to another phase with higher entropy. These results imply that the recombination of the photoexcited electrons and holes is suppressed by the screening, leading to the formation of polarons and thereby extending the lifetime. Thus, searching for organic-inorganic perovskites with high rotational entropy over a wide range of temperature may be a key to achieve superior solar cell performance.organic-inorganic hybrid perovskite | carrier lifetime | photoluminescence | polaron T he record efficiency of hybrid organic-inorganic perovskite (HOIP)-based solar cells has reached above 22% (1-4), which is comparable to that of silicon solar cells. The most dominant contribution to the high photovoltaic performance of HOIPs comes from their long carrier lifetimes (≥ 1 μs), which translates to large carrier diffusion lengths despite their modest charge mobilities (5). Several microscopic mechanisms behind the unusually long carrier lifetime have been proposed, such as formation of ferroelectric domains (6-9), Rashba effect (10-12), photon recycling (13), and large polarons (14-16). When the HOIPs are replaced with all inorganic perovskites in the solar cell architecture, the device can still function as a solar cell. This indicates that the photons excite electrons and holes out of the inorganic metal halide atoms, which is consistent with the density functional theory (DFT) calculations that the corner interstitial cations, whether organic or inorganic, do not directly contribute to the band-edge states (17). However, the efficiency of the purely inorganic perovskites is currently at ∼11% (18-20), which is far below 22% of HOIP-based solar cells. This suggests that the presence of organic cation may be the key for achieving high solar cell efficiency. It is, however, yet to be understood how the organic cations enhance the efficiency.Among the aforementioned microscopic mechanisms, three are based on the role of organic cations. First, in the ferroelectric domain theory, nanoscale ferroelectric domains are formed due to alignment of organic cations (6-9). Such domains can spatially separate the photoexcited electron and holes and thereby reduce their recombination. Second, in the Rashba effect theory (10-12), the spin and orbit degrees of freedom of the inorganic atoms are coupled with the electric field generated by the organic cations. This results in the electronic band splitting for different spins and leads to an effectively in...

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Section: Significancementioning

confidence: 92%

Origin of long lifetime of band-edge charge carriers in organic–inorganic lead iodide perovskites

Chen

Foley

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

161

179

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“…17,22,26,[54][55][56] We mention that the el-ph renormalization effects (which tend to reduce the band gap with increasing temperature) are not included in our calculation as we have mentioned earlier. As a reference, the el-ph renormalization is about 0.15 eV 59 in ZnO due to zero-point vibrations.…”

Section: 3651mentioning

confidence: 99%

“…10 Previous theoretical studies have shown a positive band gap deformation potential (a V = ∂E g /∂ln V ) of these materials. 61 We would like to point out, however, that one cannot compare directly the calculated volume-dependent band gap with the measured temperature-dependent band gap [54][55][56] by simply taking into account the thermal expansion effects. This is because the temperature-dependent el-ph effects (which tend to reduce the band gap with increasing temperature 62 ) cancel out partially the volume deformation effects (which tend to increase the band gap with increasing temperature as a result of thermal expansion and a positive deformation potential).…”

Section: 3651mentioning

confidence: 99%

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Quasiparticle band gap of organic-inorganic hybrid perovskites: Crystal structure, spin-orbit coupling, and self-energy effects

Gao

Abtew

et al. 2016

Phys. Rev. B

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The quasiparticle band gap is one of the most important materials properties for photovoltaic applications. Often the band gap of a photovoltaic material is determined (and can be controlled) by various factors, complicating predictive materials optimization. An in-depth understanding of how these factors affect the size of the gap will provide valuable guidance for new materials discovery. Here we report a comprehensive investigation on the band gap formation mechanism in organicinorganic hybrid perovskites by decoupling various contributing factors which ultimately determine their electronic structure and quasiparticle band gap. Major factors, namely, quasiparticle selfenergy, spin-orbit coupling, and structural distortions due to the presence of organic molecules, and their influences on the quasiparticle band structure of organic-inorganic hybrid perovskites are illustrated. We find that although methylammonium cations do not contribute directly to the electronic states near band edges, they play an important role in defining the band gap by introducing structural distortions and controlling the overall lattice constants. The spin-orbit coupling effects drastically reduce the electron and hole effective masses in these systems, which is beneficial for high carrier mobilities and small exciton binding energies.

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“…This is conflated with thermal lattice expansion, which also affect the band gap (larger lattice parameters give larger band gaps), and the combination of the two effects may explain why observed band gaps in MAPbI 3 increase with temperature. [25][26] More accurate calculations of electronic and opto-electronic properties of these structural models may be provided by many-body perturbation theory, 27-28 but we expect the trends discussed here to be robust. Our HERFD XAS is sensitive to both lattice parameters (demonstrated with P3 vs.…”

mentioning

confidence: 99%

Determining Atomic-Scale Structure and Composition of Organo-Lead Halide Perovskites by Combining High-Resolution X-ray Absorption Spectroscopy and First-Principles Calculations

et al. 2017

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Abstract:We combine high energy resolution fluorescence detection (HERFD) X-ray absorption spectroscopy (XAS) measurements with first-principles density functional theory (DFT) calculations to provide a molecular scale understanding of local structure, and its role in defining optoelectronic properties, in CH 3 NH 3 Pb(I 1-x Br x ) 3 perovskites. The spectra probe a ligand field splitting in the unoccupied d states of the material, which lie well above the conduction band minimum and display high sensitivity to halide identity, Pb-halide bond length, Pb-halide octahedral tilting, as well as the organic cation. We find that the halides in these mixed compositions are randomly distributed, rather than having preferred octahedral sites, and that thermal tilting motions dominate over any preferred structural distortions as a function of halide composition. These findings demonstrate the utility of the combined HERFD XAS and DFT approach for determining structural details in these materials and connecting them to optoelectronic properties observed by other characterization methods.

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Temperature dependent energy levels of methylammonium lead iodide perovskite

Cited by 169 publications

References 40 publications

Origin of long lifetime of band-edge charge carriers in organic–inorganic lead iodide perovskites

Origin of long lifetime of band-edge charge carriers in organic–inorganic lead iodide perovskites

Quasiparticle band gap of organic-inorganic hybrid perovskites: Crystal structure, spin-orbit coupling, and self-energy effects

Determining Atomic-Scale Structure and Composition of Organo-Lead Halide Perovskites by Combining High-Resolution X-ray Absorption Spectroscopy and First-Principles Calculations

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