Screening in crystalline liquids protects energetic carriers in hybrid perovskites

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Science  23 Sep 2016:
Vol. 353, Issue 6306, pp. 1409-1413
DOI: 10.1126/science.aaf9570

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  • RE: “Hot carriers in hybrid perovskites”
    • Alexander P. Kirk, Scientist, MicroLink Devices, Inc.
    • Other Contributors:
      • Drew W. Cardwell, Scientist, MicroLink Devices, Inc.
      • Joshua D. Wood, Scientist, MicroLink Devices, Inc.

    The authors of the Report “Screening in crystalline liquids protects energetic carriers in hybrid perovskites” correlate time-resolved photoluminescence (TR-PL) and time-resolved optical Kerr effect (TR-OKE) data and assert that the photogenerated hot carriers in cubic, organic lead bromide perovskites are protected by molecular reorientation of organic cation cages. They then speculate—without actual device modeling or measured I-V data—that these lead bromide perovskites could enable up to 66% efficient, Shockley-Queisser limit-breaking solar cells. Nevertheless, achieving that would require extraction of the protected hot carriers in a real solar cell, a discussion which is absent.

    Most notable is the Report’s omission of the crucial electronic band structure and phonon dispersion plots necessary to rule out conventional phonon cooling and bolster the authors’ polaron screening model. It is plausible that the lead bromide perovskites possess inherent electronic and phononic properties that promote ephemeral delays in hot carrier relaxation. Electronic—including even “defect”—quantum states that give rise to the weak “hot” luminescence could also exist. This could then explain the reported three orders of magnitude weaker above band gap (versus band-edge) luminescence in CH3NH3PbBr3 and CH(NH2)2PbBr3, but not in CsPbBr3. Without rigorous electronic band structure calculations and a detailed knowledge of the phonon dispersion, it appears impossible to eliminate wea...

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    Competing Interests: None declared.