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Time-resolved photoemission spectroscopy of electronic cooling and localization in CH3NH3PbI3 crystals

Zhesheng Chen, Min-i Lee, Zailan Zhang, Hiba Diab, Damien Garrot, Ferdinand Lédée, Pierre Fertey, Evangelos Papalazarou, Marino Marsi, Carlito Ponseca, Emmanuelle Deleporte, Antonio Tejeda, and Luca Perfetti
Phys. Rev. Materials 1, 045402 – Published 26 September 2017
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  • INTRODUCTION
  • SAMPLE CHARACTERIZATION
  • TWO-PHOTON PHOTOEMISSION
  • ULTRAFAST COOLING OF HOT ELECTRONS
  • DIFFUSION IN THE AS-GROWN SAMPLE
  • ELECTRONIC LOCALIZATION IN ANNEALED…
  • RADIATIVE AND SURFACE RECOMBINATION
  • CONCLUSIONS
  • ACKNOWLEDGMENTS
    • References

    Abstract

    We measure the surface of CH3NH3PbI3 single crystals by making use of two-photon photoemission spectroscopy. Our method monitors the electronic distribution of photoexcited electrons, explicitly discriminating the initial thermalization from slower dynamical processes. The reported results disclose the fast-dissipation channels of hot carriers (0.25 ps), set an upper bound to the surface-induced recombination velocity (<4000 cm/s), and reveal the dramatic effect of shallow traps on the electrons dynamics. The picosecond localization of excited electrons in degraded CH3NH3PbI3 samples is consistent with the progressive reduction of photoconversion efficiency in operating devices. Minimizing the density of shallow traps and solving the aging problem may boost the macroscopic efficiency of solar cells to the theoretical limit.

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    • Received 21 April 2017

    DOI:https://doi.org/10.1103/PhysRevMaterials.1.045402

    ©2017 American Physical Society

    Physics Subject Headings (PhySH)

    1. Research Areas
    DiffusionElectronic structureLocalizationSurface & interfacial phenomena
    1. Physical Systems
    Organic semiconductorsSemicrystalline polymers
    1. Techniques
    PhotoionizationPhotoluminescenceTwo-photon photoelectron spectroscopy
    Condensed Matter, Materials & Applied Physics

    Authors & Affiliations

    Zhesheng Chen1, Min-i Lee2, Zailan Zhang3, Hiba Diab4, Damien Garrot5, Ferdinand Lédée4,6, Pierre Fertey7, Evangelos Papalazarou2, Marino Marsi2, Carlito Ponseca8, Emmanuelle Deleporte4,6, Antonio Tejeda2, and Luca Perfetti1

    • 1Laboratoire des Solides Irradiés, Ecole Polytechnique, CNRS, CEA, Université Paris-Saclay, 91128 Palaiseau Cedex, France
    • 2Laboratoire de Physique des Solides, CNRS, Université Paris-Saclay, Université Paris-Sud, 91405 Orsay, France
    • 3Institut de Minéralogie et de Physique des Matériaux et de Cosmochimie (IMPMC), UMR CNRS 7590, Université Pierre et Marie Curie - Case 115, 4, Place Jussieu, 75252 Paris Cedex 05, France
    • 4Laboratoire Aimé Cotton, Ecole Normale Supérieure ENS Paris-Saclay, CNRS, Université Paris-Sud, Université Paris-Saclay, 91405 Orsay, France
    • 5Groupe d'Etudes de la Matière Condensée (GEMaC), CNRS, Université de Versailles, Saint-Quentin-en-Yvelines, Université Paris-Saclay, 45 Avenue des Etats-Unis, 78035 Versaille Cedex, France
    • 6Laboratoire de Photophysique et Photochimie Supramoléculaires et Macromoléculaires de l'Ecole Normale Supérieure de Cachan, 61 Avenue du Président Wilson, 94235 Cachan, France
    • 7Société Civile Synchrotron SOLEIL, L'Orme des Merisiers, Saint-Aubin - BP 48, 91192 Gif-sur-Yvette, France
    • 8Division of Chemical Physics, Lund University, Box 124, 221 00 Lund, Sweden

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    Issue

    Vol. 1, Iss. 4 — September 2017

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    Images

    • Figure 1
      Figure 1

      (a) Image of a single MAPbI3 crystal acquired by scanning electron microscope. (b) X-ray diffraction of Bragg peaks in the {0,k⊥,k||} plane of the tetragonal phase. (c) Intensity map of photoluminescence as function of photon energy and sample temperature. The abrupt transition around 160 K is due to the tetragonal to orthorhombic phase transition. (d) Photoluminescence spectrum of MAPbI3 measured at 130 K.

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    • Figure 2
      Figure 2

      (a) Photoelectron intensity map acquired with photon energy of 94 eV in the {k||,k⊥∼0, 0} direction of the tetragonal phase. (b) Wave-vector-integrated photoelectron spectrum acquired with photon energy of 94 eV. The maximum of the valence band is located 1.6 eV below the chemical potential.

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    • Figure 3
      Figure 3

      (a) Band structure of MAPbI3 freely adapted from Filip et al. [18]. The green arrows stand for direct transitions induced by photons with hν1=3.15eV. (b) Energetics of the 2PPE experiment with pump photon energy hν1, probe photon energy hν2, band gap Δg, chemical potential μF, and analyzer work function ϕ.

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    • Figure 4
      Figure 4

      (a) Photoelectron intensity map in the as-grown sample as a function of kinetic energy and pump-probe delay. (b) Energy distribution curves acquired at different values of the pump-probe delay and normalized to their maximum value. (c) Evolution of the average kinetic energy as a function of time. The solid line is an exponential fit with time constant τ1=0.25 ps.

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    • Figure 5
      Figure 5

      (a) The density profile of photoexcited electrons is calculated by the diffusion model of Eq. (1) for selected delay times. (b) The integrated intensity of the 2PPE signal (black marks) as a function of time is compared with the diffusion model (red line). The dotted blue line at t=3τ1 indicates the delay time when electrons have fully thermalized.

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    • Figure 6
      Figure 6

      (a) Photoluminescence spectra acquired as grown, 100∘C annealed, and 200∘C samples. The dashed line is a guide to the eye showing the development of trapped states upon annealing. Photoelectron intensity map in samples annealed at 100∘C (b) and 200∘C (c). (d) Temporal evolution of the integrated 2PPE signal in the pristine and annealed samples. The arrows indicate the characteristic time scale when electronic trapping takes place.

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    • Figure 7
      Figure 7

      Photoluminescence emitted in the visible spectral range from the MA200 sample at 10 K. The peak centered at 2.45 eV arises from carrier recombination in PbI2 inclusions.

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    • Figure 8
      Figure 8

      Temporal evolution of the integrated 2PPE signal in the sample annealed at 100∘C (blue marks) and 200∘C (green marks). The red line is a fitting curve with bimolecular recombination rate γ=4±1×10−10cm3/s whereas the yellow line (which is almost indistinguishable from the red line) is the fit obtained by Eq. (2) with S=4000 cm/s and DT=0.05cm2/s.

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