Fig. 4: Compositional evolution of Cs–Pb–Br polymorphs and the underlying kinetics of competing reaction paths.

a ¹³³Cs MAS ssNMR spectra of samples with different milling times at 10 kHz MAS and 300 K. CsBr, Cs₄PbBr₆, CsPbBr₃, and CsPb₂Br₅ peaks are marked with semi-transparent yellow, black, red, and purple strips, respectively. The remaining peaks correspond to spinning side bands. Inset shows magnified spectra of 20 and 90-min samples (red and yellow line, respectively). The full spectra of a are given in Supplementary Fig. 19. b Weight fractions of precursors and synthesized Cs–Pb–Br perovskites for each sample calculated through Rietveld refinement process. The same graph shown in molar fraction can be found in Supplementary Fig. 21. The dividing of stages coincides with the near consumption of PbBr₂ (below 2 wt%) and different reaction paths contributing to these stages are labeled as Path A and Path B. The green gradient is marked at the same region as in Fig. 2b. c A schematic reaction kinetics diagram of two competing paths (Paths A and B) in the synthesis of 0D Cs₄PbBr₆ from the precursors. Formation enthalpy of CsPbBr₃ (22 kJ/mol) and Cs₄PbBr₆ (38 kJ/mol) are from ref. ²⁴. The inset illustrates the potential origin of difference between the two activation energies of E_0D and E_3D. Source data are provided as a Source Data file.