Colloidal Synthesis and Charge‐Carrier Dynamics of Cs2AgSb1‐yBiyX6 (X: Br, Cl; 0 ≤y ≤ 1) Double Perovskite Nanocrystals

A series of lead‐free double perovskite NCs: Cs2AgSb1‐yBiyX6 (X: Br, Cl; 0≤y≤1) NCs are synthesized. In particular, Cs2AgSbBr6 NCs is a new double perovskite material that has not been reported for the bulk form. Mixed Ag‐Sb/Bi NCs exhibit enhanced stability in colloidal solution compared to Ag‐Bi or Ag‐Sb NCs. Femtosecond transient absorption studies indicate the presence of two prominent fast trapping processes in the charge carrier relaxation. The two fast trapping processes are dominated by intrinsic self‐trapping (1~2 ps) due to giant exciton‐phonon coupling and surface defects trapping (50~100 ps), respectively. In addition, hot‐carrier relaxation is obviously slowed down at high pump fluence.

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