Lead-free halide double perovskites with the formula of quaternary $A_2^{+}{B}^{+}{B}^{{\mathrm{\prime }}^{3+}}{X}_6^{-}$ have recently attracted intense interest as alternatives to lead-halide-perovskite-based optoelectronic materials for their nontoxicity and enhanced chemical and thermodynamic stability. However, the understanding of intrinsic defect properties and their effects on carrier transport and Fermi level tuning is still limited. In this paper, we show that, by exploring the phase diagram of a halide double perovskite, one can control the effects of intrinsic defects on carrier trapping and Fermi-level pinning. We reveal the ideal growth conditions to grow p type ${\mathrm{Cs}}_2\mathrm{Ag}\mathrm{In}{\mathrm{Cl}}_6$ and ${\mathrm{Cs}}_2\mathrm{Ag}\mathrm{Bi}{\mathrm{Cl}}_6$ as well as semi-insulating ${\mathrm{Cs}}_2\mathrm{Ag}\mathrm{Bi}{\mathrm{Br}}_6$ with low trap density for targeted photovoltaic or visible light/radiation detection application.

• Received 17 December 2017
• Revised 27 March 2018

DOI:https://doi.org/10.1103/PhysRevApplied.10.041001