Tailoring the Bandgap of Cs₂AgInCl₆ Nanocrystals through Fe Alloying for Optoelectronic Applications

All inorganic metal–halide perovskite nanocrystals (NCs) have attracted great interest due to their potential application in optoelectronic devices. Herein, for the first time, we report the facile synthesis of Fe3+ alloyed Cs2AgInCl6 double perovskite nanocrystals using the hot injection method. In the pristine structure, Fe3+ is found to partially replace In3+ resulting in the shrinkage of the lattice while retaining the double perovskite structure up to 30% alloying. This is confirmed from both X-ray diffraction patterns (XRD) as well as electron spin resonance spectroscopy (ESR). By varying the amount of Fe3+ alloyed into the double perovskite system, the bandgap was significantly tuned from 3.05 to 2.0 eV. Photoluminescence (PL) and time-resolved photoluminescence (TRPL) measurements were carried out on Fe3+ alloyed Cs2AgInCl6 double perovskite NCs. It was found that Fe3+ alloying resulted in the formation of midgap states, which thereby reduce the PL intensity and promote nonradiative recombination pathways. Efficient photodetectors were fabricated by utilizing the reduced bandgap of the NCs, and the alloyed NCs showed a better light response along with a sharper on and off ratio over the pristine NCs.