Based on density function theory calculations and molecular dynamics simulations, the chemical potential-dependent formation energies of various defects and the most detrimental point defect for the ra-diative recombination of charge carriers in targeted systems can be known. Using these critical information as a guidline, colloidal synthesis strategies that benifit the suppression of defect formation are designed. By this means, I have sucessfully synthesized highly luminescent tin halide perovskite nanocrystals, and will use the concept of "theory-guided synthetic chemistry" to synthesize more nanocrystals with excellent optical properties.