Equal Footing of Thermal Expansion and Electron–Phonon Interaction in the Temperature Dependence of Lead Halide Perovskite Band Gaps

Francisco‐López, Adrián; Charles, Bethan; Weber, Oliver J.; Alonso, M. I.; Garriga, M.; Campoy‐Quiles, Mariano; Weller, Mark T.; Goñi, A. R.

doi:10.1021/acs.jpclett.9b00876

Cited by 79 publications

(85 citation statements)

References 40 publications

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“…This appears to be a general trend in metal halide perovskites, [ 16,24,29,31,32 ] in frank contrast with the flat plateau exhibited by the gap of most tetrahedrally bonded semiconductors. [ 33 ] It turns out that such unusual temperature‐induced renormalization of the band gap in the perovskites is partly due to a peculiar electron–phonon interaction, [ 34 ] determined by the coupling to the very low‐frequency modes of the inorganic cage. [ 35–37 ]…”

Section: Resultsmentioning

confidence: 99%

Photoluminescence of Bound‐Exciton Complexes and Assignment to Shallow Defects in Methylammonium/Formamidinium Lead Iodide Mixed Crystals

Francisco‐López

Charles

Alonso

et al. 2021

Advanced Optical Materials

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The high defect tolerance of metal halide perovskites, in terms of their exceptional optoelectronic properties, is assumed to be due to the very fact that most native point defects are shallow, which does not contribute to the non‐radiative recombination of free carriers. Here, a systematic study is presented, which concerns the evolution of shallow‐defect signatures observed at low temperatures in the photoluminescence (PL) spectra of mixed organic‐cation lead iodide perovskite single crystals (FAxMA1−xPbI3, where MA stands for methylammonium and FA for formamidinium). Below ≈100 K, a number of peak‐like features become clearly apparent in the PL spectra at energies lower than the strong free‐exciton emission, which are related to the radiative recombination of bound exciton complexes associated with native shallow defects (donors and/or acceptors). Based on state‐of‐the‐art ab initio calculations, a tentative assignment is provided for all PL features to different shallow‐defects (Pb, I, and MA vacancies as well as I interstitials) typically present in hybrid perovskites. The defect‐related signatures exhibit a clear trend regarding the mixed‐crystal composition, indicating that the material becomes less prone to defect formation with increasing FA content.

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Section: Resultsmentioning

confidence: 99%

Photoluminescence of Bound‐Exciton Complexes and Assignment to Shallow Defects in Methylammonium/Formamidinium Lead Iodide Mixed Crystals

Francisco‐López

Charles

Alonso

et al. 2021

Advanced Optical Materials

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“…It should be noted that the red‐shifted PL does not necessarily mean an increased population of in‐band states or impurities (as those generally serve a nonradiative recombination center) but a characteristic of MAPbI 3 perovskites identified in both poly‐ or mono‐crystalline forms. [ 31,33–35 ] The indicated reduction of E g at lower T may partially contribute to the enlargement of J SC (provided that the absorption coefficient of tetragonal MAPbI 3 is roughly T ‐invariable [ 33 ] ). Given the reduced E g (with reducing T ), the saturation trend of V OC at lower T may also be reconciled.…”

Section: Resultsmentioning

confidence: 99%

Understanding Temperature‐Dependent Charge Extraction and Trapping in Perovskite Solar Cells

Zhou

Wang

Meng

et al. 2020

Adv Funct Materials

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Understanding the factors that limit the performance of perovskite solar cells (PSCs) can be enriched by detailed temperature (T)-dependent studies. Based on p-i-n type PSCs with prototype methylammonium lead triiodide (MAPbI 3 ) perovskite absorbers, T-dependent photovoltaic properties are explored and negative T-coefficients for the three device parameters (V OC , J SC , and FF) are observed within a wide low T-range, leading to a maximum power conversion efficiency (PCE) of 21.4% with an impressive fill factor (FF) approaching 82% at 220 K. These T-behaviors are explained by the enhanced interfacial charge transfer, reduced charge trapping with suppressed nonradiative recombination and narrowed optical bandgap at lower T. By comparing the T-dependent device behaviors based on MAPbI 3 devices containing a PASP passivation layer, enhanced PCE at room temperature is observed but different tendencies showing attenuating T-dependencies of J SC and FF, which eventually leads to nearly T-invariable PCEs. These results indicate that charge extraction with the utilized all-organic charge transporting layers is not a limiting factor for low-T device operation, meanwhile the trap passivation layer of choice can play a role in the T-dependent photovoltaic properties and thus needs to be considered for PSCs operating in a temperature-variable environment.

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“…Computational modeling has attributed the increase in bandgap upon temperature increase to electron-phonon coupling and thermal expansion. 197,207,208 Interestingly, we recently observed a ~30 meV red shift in the PL spectrum of MAPbI 3 across the tetragonal-cubic transition when MAPbI 3 crystals were nanoconfined in the ~20 -250 diameter pores of AAO (Figure 9), 150 opposite of the trend observed in bulk crystals. By increasing the surface area-tovolume ratio of these crystals, nanoconfinement shifted the relative Gibbs free energies of the , , and  phases such that the - transition temperature was lowered from ~330 K to between 170 -200 K. At these lower temperatures, thermal fluctuations in the M-X framework are likely suppressed, resulting in a narrowing of the bandgap upon transitioning to the cubic phase with I-Pb-I angles of 180 o .…”

Section: Materials Advances Accepted Manuscriptmentioning

confidence: 90%

Polymorphism in metal halide perovskites

et al. 2021

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Equal Footing of Thermal Expansion and Electron–Phonon Interaction in the Temperature Dependence of Lead Halide Perovskite Band Gaps

Abstract: Lead halide perovskites, which are causing a paradigm shift in photovoltaics, exhibit an atypical temperature dependence of the fundamental gap: it decreases in energy with decreasing temperature. Reports ascribe such a behavior to a strong electron-phonon renormalization

Cited by 79 publications

References 40 publications

Photoluminescence of Bound‐Exciton Complexes and Assignment to Shallow Defects in Methylammonium/Formamidinium Lead Iodide Mixed Crystals

Photoluminescence of Bound‐Exciton Complexes and Assignment to Shallow Defects in Methylammonium/Formamidinium Lead Iodide Mixed Crystals

Understanding Temperature‐Dependent Charge Extraction and Trapping in Perovskite Solar Cells

Polymorphism in metal halide perovskites

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