Compositional Tuning of Carrier Dynamics in Cs<sub>2</sub>Na<sub>1–<i>x</i></sub>Ag<sub><i>x</i></sub>BiCl<sub>6</sub> Double-Perovskite Nanocrystals
Dongxu Zhu, Juliette Zito, Valerio Pinchetti, Zhiya Dang, Andrea Olivati, Lea Pasquale, Aiwei Tang, Matteo L. Zaffalon, Francesco Meinardi, Ivan Infante, Luca De Trizio, Liberato Manna, Sergio Brovelli
Abstract
We devised a hot-injection synthesis to prepare colloidal double-perovskite Cs2NaBiCl6 nanocrystals (NCs). We also examined the effects of replacing Na+ with Ag+ cations by preparing and characterizing Cs2Na1–xAgxBiCl6 alloy NCs with x ranging from 0 to 1. Whereas Cs2NaBiCl6 NCs were not emissive, Cs2Na1–xAgxBiCl6 NCs featured a broad photoluminescence band at ∼690 nm, Stokes-shifted from the respective absorption by ≥1.5 eV. The emission efficiency was maximized for low Ag+ amounts, reaching ∼3% for the Cs2Na0.95Ag0.05BiCl6 composition. Density functional theory calculations coupled with spectroscopic investigations revealed that Cs2Na1–xAgxBiCl6 NCs are characterized by a complex photophysics stemming from the interplay of (i) radiative recombination via trapped excitons localized in spatially connected AgCl6–BiCl6 octahedra; (ii) surface traps, located on undercoordinated surface Bi centers, behaving as phonon-assisted nonradiative decay channels; and (iii) a thermal equilibrium between trapping and detrapping processes. These results offer insights into developing double-perovskite NCs with enhanced optoelectronic efficiency.