Abstract
Metal halide perovskites exhibit a fairly linear increase of the bandgap with increasing temperature, when crystallized in a tetragonal or cubic phase. In general, both thermal expansion and electron-phonon interaction effects contribute equally to this variation of the gap with temperature. Herein, we have disentangled both contributions in the case of colloidal CsPbBr(3) nanocrystals (NCs) by means of photoluminescence (PL) measurements as a function of temperature (from 80 K to ambient) and hydrostatic pressure (from atmospheric to ca. 1 GPa). At around room temperature, CsPbBr(3) NCs also show a linear increase of the bandgap with temperature with a slope similar to that of the archetypal methylammonium lead iodide (MAPbI(3)) perovskite. This is somehow unexpected in view of the recent observations in mixed-cation Cs (x) MA(1-x) PbI(3) single crystals with low Cs content, for which Cs incorporation caused a reduction by a factor of 2 in the temperature slope of the gap. This effect was ascribed to an anomalous electron-phonon interaction induced by the coupling with vibrational modes admixed with the Cs translational dynamics inside the cage voids. Thus, no trace of anomalous coupling is found in CsPbBr(3) NCs. However, we managed to show that the linear temperature renormalization exhibited by the gap of CsPbBr(3) NCs is shared with most metal halide perovskites, due to a common bonding/antibonding and atomic orbital character of the electronic band-edge states. In this way, we provide a deeper understanding of the gap temperature dependence in the general case when the A-site cation dynamics is not involved in the electron-phonon interaction.