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. 2020 Feb 14;6(7):eaaw7453.
doi: 10.1126/sciadv.aaw7453. eCollection 2020 Feb.

Low-frequency lattice phonons in halide perovskites explain high defect tolerance toward electron-hole recombination

Weibin Chu  1   2 , Qijing Zheng  1 , Oleg V Prezhdo  2 , Jin Zhao  1   3   4 , Wissam A Saidi  5
Affiliations

Low-frequency lattice phonons in halide perovskites explain high defect tolerance toward electron-hole recombination

Weibin Chu et al. Sci Adv. .

Abstract

Low-cost solution-based synthesis of metal halide perovskites (MHPs) invariably introduces defects in the system, which could form Shockley-Read-Hall (SRH) electron-hole recombination centers detrimental to solar conversion efficiency. Here, we investigate the nonradiative recombination processes due to native point defects in methylammonium lead halide (MAPbI3) perovskites using ab initio nonadiabatic molecular dynamics within surface-hopping framework. Regardless of whether the defects introduce a shallow or deep band state, we find that charge recombination in MAPbI3 is not enhanced, contrary to predictions from SRH theory. We demonstrate that this strong tolerance against defects, and hence the breakdown of SRH, arises because the photogenerated carriers are only coupled with low-frequency phonons and electron and hole states overlap weakly. Both factors appreciably decrease the nonadiabatic coupling. We argue that the soft nature of the inorganic lattice with small bulk modulus is key for defect tolerance, and hence, the findings are general to other MHPs.

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Figures

Fig. 1
Fig. 1. Atom-projected DOS for different defective and pristine MAPbI3.
(A to F) Defective and Pristine systems of MAPbI3. The energy reference is located at the Fermi level. Inset shows corresponding atomic structure, with blue circle indicating the defect location.
Fig. 2
Fig. 2. The time evolution of the VBM, the CBM, and the defect state for MAPbI3 systems at 300 K.
(A to F) Defective and Pristine systems of MAPbI3. The energy reference is located at the VBM of the initial configuration.
Fig. 3
Fig. 3. The e-h recombination process in MAPbI3 systems.
(A) Schematic map of the direct and by-defect e-h recombination processes. (B) e-h recombined percentage for different systems after 2 ns. The direct and by-defect e-h recombined percentages are shown by blue and green color bars. (C and D) Time-dependent e-h recombined percentage for different systems. The direct and by-defect e-h recombined percentage is shown in (C) and (D), respectively.
Fig. 4
Fig. 4. The Fourier transform spectra of the autocorrelation function of the VBM, the CBM, and the defect state energies.
(A to F) Defective and Pristine systems of MAPbI3.
Fig. 5
Fig. 5. Orbital spatial distribution of the VBM, the CBM, and the defect states of the MAPbI3 systems.
(A to F) Defective and Pristine systems. Orange circles indicate the defect location.
See this image and copyright information in PMC

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