Absence of a polaron signature in angle-resolved photoemission of CsPbBr₃

The formation of large polarons has been proposed as reason for the high defect tolerance, low mobility, low charge carrier trapping and low nonradiative recombination rates of lead halide perovskites. In polaronic oxides TiO₂ and SrTiO₃, polarons lead to an enhanced effective mass in angle-resolved photoemission spectroscopy (ARPES). Recently, evidence for large-polaron formation in CsPbBr₃ has been reported from a 50% effective mass enhancement in ARPES relative to band structure calculations [1]. We present in-depth band dispersion measurements of CsPbBr₃ to determine the R-point in momentum space and GW calculations that lead to a realistic band gap. We obtain almost identical effective masses at the valence band maximum of 0:202+/-0:016 m₀ in experiment and 0.18 m₀ (cubic) to 0.223 m₀ (orthorhombic) in theory. This means that there is no indication for large polaron formation from ARPES data.

[1] M. Puppin et al., Phys. Rev. Lett. 124, 206402 (2020).