Fig. 4.

Formation process model adopted for the discussion of perovskite nanocrystal (NC) growth: Variation of the precursor concentration with time (a.u.) for four different cases (1–4). Upper frame shows positions of PL spectra for the perovskite NCs characteristic for certain discussed cases, indicated by vertical dashed lines. In the first case, the concentration of the precursors is too low (0.01×) for any nucleation process. In the second case, the precursors’ concentration (0.33×) is not yet high enough to allow for much growth of the NCs after nucleation, but will be sufficient for the formation of small NCs. In the third case, with more precursors available in the reaction mixture (1×), the probability of the formation of larger perovskite micro-particles becomes higher. There are two competing processes: nucleation with and without further growth, while the formation of larger NCs for higher precursor concentrations is more likely to happen, and the amount of the non-NC precipitate is increased. In the fourth case, at the highest employed precursor concentration (2.33×), the nucleation and growth always happen until the excess concentration of the precursor falls to a low enough level