Halide double perovskites,
A
2
M
I
M
III
X
6
, offer a vast
chemical space for obtaining unexplored
materials with exciting properties for a wide range of applications.
The photovoltaic performance of halide double perovskites has been
limited due to the large and/or indirect bandgap of the presently
known materials. However, their applications extend beyond outdoor
photovoltaics, as halide double perovskites exhibit properties suitable
for memory devices, indoor photovoltaics, X-ray detectors, light-emitting
diodes, temperature and humidity sensors, photocatalysts, and many
more. This Perspective highlights challenges associated with the synthesis
and characterization of halide double perovskites and offers an outlook
on the potential use of some of the properties exhibited by this so
far underexplored class of materials.