Fully inorganic lead halide perovskites nanocrystals (NCs) are emerging as extremely interesting active materials for a wide variety of optoelectronic and photonic devices, due to their capability to combine easy synthesis in solution, high photoluminescence quantum yield, ultra-wide color gamut, very high optical gain at room temperature, simple deposition in thin films by using wet techniques and improved stability with respect to organic-inorganic NCs. Among these materials CsPbBr3 NCs are particularly interesting for light emitting devices in the visible, thanks to their bright emission in the green that candidates them as very promising semiconductors able to close the so called "green-gap" of semiconductors. A deep understanding of their photophysics is thus fundamental to properly understand the origin of the material active properties and provide strategies to improve them.

In this frame, a particularly powerful approach is the investigation of the temperature dependence of the Photoluminescence (PL) spectra and of the PL relaxation dynamics that allows to explore several features, like the interplay between radiative and non-radiative relaxation processes, the origin of the emitting states (free carriers or excitons), and the coupling with phonons.

To date the PL temperature dependence has been often used to determine fundamental quantities of CsPbBr3 NCs, like the LO phonon energy and the exciton binding energy, interestingly obtaining widely scattered, and inconsistent each other, values.

In this work we exploit the local morphology variations of a drop cast CsPbBr3 nanocrystals thin film to evidence that NCs aggregation has strong effects on the PL spectra peak wavelength, linewidth and intensity temperature dependence. We demonstrate that an analysis based on frequently used models in literature lead to completely different conclusions about the intrinsic NCs emission properties extracted from spectra measured in points with different contribution of the PL from the aggregates. A more careful analysis instead allows to ascribe the inconsistencies to the different contribution of NCs aggregates to the total PL and to determine in which conditions the PL is mainly due to the NCs and in which ones to their aggregates. Our results demonstrate that extreme care has to be used in order to correctly correlate the PL spectral features to the intrinsic emission properties of lead halide perovskites NCs films, and that the investigation of the local morphology is fundamental to avoid wrong conclusions.