Synthesis\nand Optical Properties of Lead-Free Cesium\nTin Halide Perovskite Nanocrystals

Abstract

Metal\nhalide perovskite crystal structures have emerged as a class\nof optoelectronic materials, which combine the ease of solution processability\nwith excellent optical absorption and emission qualities. Restricting\nthe physical dimensions of the perovskite crystallites to a few nanometers\ncan also unlock spatial confinement effects, which allow large spectral\ntunability and high luminescence quantum yields at low excitation\ndensities. However, the most promising perovskite structures rely\non lead as a cationic species, thereby hindering commercial application.\nThe replacement of lead with nontoxic alternatives such as tin has\nbeen demonstrated in bulk films, but not in spatially confined nanocrystals.\nHere, we synthesize CsSnX₃ (X = Cl, Cl_0.5Br_0.5, Br, Br_0.5I_0.5, I) perovskite nanocrystals\nand provide evidence of their spectral tunability through both quantum\nconfinement effects and control of the anionic composition. We show\nthat luminescence from Sn-based perovskite nanocrystals occurs on\npico- to nanosecond time scales via two spectrally distinct radiative\ndecay processes, which we assign to band-to-band emission and radiative\nrecombination at shallow intrinsic defect sites.