Optimal colloidal synthesis and quality judgment of low-dimensional Cs3Cu2Cl5 nanocrystals with efficient green emission

Low-dimensional copper (I)-based ternary metal halides, having the features of nontoxicity, outstanding optical performance and great air-stability, is becoming the promising substitutes for traditional metal perovskite halides. Despite the impressive progress in copper halides, highly effective synthesis of their nanocrystals with precise shape and size control, compared to that of conventional lead halide semiconductors, is still remained to be explored. In this work, we report a systematically optimized finds for the colloidal synthesis conditions of Cs3Cu2Cl5 nanocrystals (NCs). The Cs3Cu2Cl5 NCs are modulated from nanoparticles to nanorods and to nanoplates by adjusting reaction temperature and reaction time. Cs3Cu2Cl5 nanorods give a wide emission at 510 nm, being caused by self-trapped exciton state with exciton binding energy of 137 meV and phonon–electron interaction of 25 meV as determined by temperature-dependent photoluminescence spectra. The photoluminescence quantum yield (PLQY) of the nanorods that were reacted at 150 °C for 1200 s, an optimal reaction condition, reaches up to 80.19%. We also find for the first time that the optical quality of Cs3Cu2Cl5 NCs is positively related to the full width at half maximum of main peak in X-ray diffraction pattern. The findings in this work give a view to the future planning for Cs3Cu2Cl5's colloidal synthesis and raise an intuitive criterion for the quality of as-synthesized Cs3Cu2Cl5 NCs.