Lead-Free Silver-Bismuth Halide Double Perovskite Nanocrystals.

Lead-free perovskite nanocrystals (NCs) were obtained mainly by substituting a Pb2+ cation with a divalent cation or substituting three Pb2+ cations with two trivalent cations. The substitution of two Pb2+ cations with one monovalent Ag+ and one trivalent Bi3+ cations was used to synthesize Cs2 AgBiX6 (X=Cl, Br, I) double perovskite NCs. Using femtosecond transient absorption spectroscopy, the charge carrier relaxation mechanism was elucidated in the double perovskite NCs. The Cs2 AgBiBr6 NCs exhibit ultrafast hot-carrier cooling (<1 ps), which competes with the carrier trapping processes (mainly originate from the surface defects). Notably, the photoluminescence can be increased by 100 times with surfactant (oleic acid) added to passivate the defects in Cs2 AgBiCl6 NCs. These results suggest that the double perovskite NCs could be potential materials for optoelectronic applications by better controlling the surface defects.