Research ArticleCHEMICAL PHYSICS

Protecting hot carriers by tuning hybrid perovskite structures with alkali cations

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Science Advances  23 Oct 2020:
Vol. 6, no. 43, eabb1336
DOI: 10.1126/sciadv.abb1336
  • Fig. 1 Structural and optoelectronic properties modulated by alkali cations.

    (A) XRD patterns, (B) the lattice constants, and (C) the FWHM of the perovskite peak. The lattice constants and FWHM were extracted from the peak at around 14°. a.u., arbitrary unit. (D) Steady-state PL spectra. (E) Time-resolved PL decay curves for samples with different cation combinations. Elongation of PL lifetime is observed with the addition of alkali cations.

  • Fig. 2 Hot carrier cooling modulated by alkali cations.

    (A and B) Normalized TA spectra of pump at 3.10 eV with excitation density of 1.3 × 1018 cm−3 at different pump-probe delays for MAFA (A) and RbCsKMAFA (B), respectively. Spectral broadening at early delay time indicates hot carrier distributions. The black dashed lines are fits to the high-energy bleach tail with the Maxwell-Boltzmann distribution to extract effective carrier temperature Tc, as described in the main text. (C and D) Extracted Tc of MAFA and RbCsKMAFA as a function of delay time at different carrier densities. (E) Carrier cooling curves for different samples at N0 of 1.3 × 1018 cm−3, displaying strong dependence on alkali cations. (F) Similar initial Tc and cooling behavior can be achieved in RbCsKMAFA with an order of magnitude lower N0 than the reference MAFA (3 × 1017 versus 3 × 1018 cm−3). Solid lines are the fitted with biexponential or triexponential functions, and the fitting parameters are given in table S1.

  • Fig. 3 Ab initio calculations on the effect of Ivs on carrier cooling.

    (A and B) Atom-projected DOS for pristine MAPbI3 (A) and lattice with Iv (B) for representative structures at 300 K. The zero of energy is at the Fermi level. The insets show atomic structures, with the red circle indicating the defect location. The Iv introduces a strong peak in the DOS near the CBM, highlighted with the blue oval. The increased DOS accelerates hot electron cooling. (C) Hot electron relaxation. The relaxation is accelerated by Iv due to the increased DOS near the CBM.

  • Fig. 4 Enhancing hot carrier transport by alkali cations.

    (A) The TAM images of the carrier transport in RbCsKMAFA at various delay times. Probe energy = 1.65 eV, pump energy = 3.10 eV, and N0 = 5.0 × 1017 cm−3. The color scale represents the intensity of pump-induced differential transmission (ΔT) of the probe, and every image has been normalized by peak value. Scale bar, 500 nm. (B) Cross sections of the TAM images shown in (A) fitted with Gaussian functions, with the maximum ∆T signal normalized. (C) σt2 plotted as a function of pump-probe delay time, comparing hot carrier transport in MAFA, RbCsMAFA, and RbCsKMAFA. Probe energy = 1.65 eV. The dashed lines are guide to the eye. More rapid hot carrier transport is observed in RbCsMAFA and RbCsKMAFA than in MAFA. The error bars of σt2 indicate the uncertainties of the Gaussian fitting. (D) Transport of cooled carriers; σt2 at time delay >500 ps for MAFA, RbCsMAFA, and RbCsKMAFA at N0 = 5.0 × 1017 cm−3. (E and F) Longer-range hot carrier transport is observed at higher carrier density for RbCsKMAFA (E) and RbCsMAFA (F). σt2 plotted as a function of pump-probe delay time under different excitation densities.

Supplementary Materials

  • Supplementary Materials

    Protecting hot carriers by tuning hybrid perovskite structures with alkali cations

    Ti Wang, Linrui Jin, Juanita Hidalgo, Weibin Chu, Jordan M. Snaider, Shibin Deng, Tong Zhu, Barry Lai, Oleg Prezhdo, Juan-Pablo Correa-Baena, Libai Huang

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    This PDF file includes:

    • Notes S1 to S3
    • Figs. S1 to S10
    • Table S1
    • References

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