Research ArticlePHYSICS

Strong self-trapping by deformation potential limits photovoltaic performance in bismuth double perovskite

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Science Advances  17 Feb 2021:
Vol. 7, no. 8, eabd3160
DOI: 10.1126/sciadv.abd3160
  • Fig. 1 Basic properties of Cs2AgBiBr6 and solar cell performance.

    (A) Crystal structure of Cs2AgBiBr6. (B) XRD pattern of powdered Cs2AgBiBr6 SC. Inset: An image of Cs2AgBiBr6 SCs of several millimeters. a.u., arbitrary units. (C) SEM image of Cs2AgBiBr6 PC film. Inset: Zoom-in SEM image. (D) Absorption (Abs) and emission spectra of Cs2AgBiBr6 PC film and SC. UV-vis, ultraviolet-visible; DR, diffuse reflectance. (E) J-V and (F) IPCE curves of a typical Cs2AgBiBr6 solar cell with ITO/compact TiO2/Cs2AgBiBr6/Spiro-MeOTAD/Au planar structure. EQE, external quantum efficiency.

  • Fig. 2 The PL characteristics of Cs2AgBiBr6 SC and PC films.

    (A) Schematic of the phonon-assisted transitions at the indirect band edge for a typical indirect semiconductor. VB, valence band; CB, conduction band; Egd, direct band gap; Egi, indirect band gap. (B) Carrier density–dependent initial PL intensity of Cs2AgBiBr6 SC with 530-nm excitation. (C) The PLQYs of Cs2AgBiBr6 SC and PC film. The SC was excited using 532-nm (blue) and 473-nm (green) lasers at room temperature (RT). The PC film was excited using a 473-nm laser. (D) Fluence-dependent PL decays of Cs2AgBiBr6 SC upon 530-nm laser excitation. (E) Excitation energy–dependent PL kinetics of Cs2AgBiBr6 SC. Lines: Fitted curves with the model in the main text. (F) Temperature-dependent PL linewidth of Cs2AgBiBr6 SC. Dashed line, fitting with the conventional model for weak coupling; solid line, fitting with the model proposed by Toyozawa (39) for strong coupling.

  • Fig. 3 Strong coherent phonons and ultrafast polaron formation.

    (A) Pseudo color map of the TR profile of Cs2AgBiBr6 SC. (B) Top: The TR spectrum of Cs2AgBiBr6 SC monitored at 1-ps delay upon 500-nm excitation. Bottom: The transformed TA spectrum of Cs2AgBiBr6 SC using the Kramers-Kronig relations. (C) The recovery from the blue shift of the TR spectra at early delay time. (D) The TR kinetics of Cs2AgBiBr6 SC probed near the DE resonance at 440 nm in TRS measurement. (E) The terahertz transmission kinetics of Cs2AgBiBr6 PC in TRTS measurement. (F) Strong optical and acoustic modes coupled to the electronic dynamics probed near the isochromatic point (~2.83 eV). At room temperature (292 K), only the optical mode is obvious. At low temperature (78 K), the acoustic mode becomes apparent. Blue and red lines, fitted curves using Eq. 3; green line, extracted optical mode oscillations at 78 K; yellow line, extracted acoustic mode oscillations at 78 K.

  • Fig. 4 Strong CAP and self-trapping by deformation potential.

    (A) Normalized TR kinetics at 740 nm for Cs2AgBiBr6 SC upon different excitations (300, 400, and 500 nm) showing different relative CAP amplitudes. (B) A linear fit of the relative CAP amplitudes versus excitation energy to extract the deformation potentials. (C) A schematic of the self-trapping of charge carriers by acoustic phonons (deformation potential). The dots between adjacent perovskite octahedra represent the omitted lattice units for simplicity. (D) A schematic of the energy diagram for carrier self-trapping under the generalized coordinate.

Supplementary Materials

  • Supplementary Materials

    Strong self-trapping by deformation potential limits photovoltaic performance in bismuth double perovskite

    Bo Wu, Weihua Ning, Qiang Xu, Manukumara Manjappa, Minjun Feng, Senyun Ye, Jianhui Fu, Stener Lie, Tingting Yin, Feng Wang, Teck Wee Goh, Padinhare Cholakkal Harikesh, Yong Kang Eugene Tay, Ze Xiang Shen, Fuqiang Huang, Ranjan Singh, Guofu Zhou, Feng Gao, Tze Chien Sum

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