  Cs2AgBiBr6 (CABB) has been proposed as a promising non-toxic alternative to
lead halide perovskites. However, low charge carrier collection efficiencies
remain an obstacle for the incorporation of this material in optoelectronic
applications. In this work, we study the optoelectronic properties of CABB thin
films using steady state and transient absorption and reflectance spectroscopy.
We find that optical measurements on such thin films are distorted as a
consequence of multiple reflections within the film. Moreover, we discuss the
pathways behind conductivity loss in these thin films, using a combination of
microsecond transient absorption and time-resolved microwave conductivity
spectroscopy. We demonstrate that a combined effect of carrier loss and
localization results in the conductivity loss in CABB thin films. Moreover, we
find that the charge carrier diffusion length and sample thickness are of the
same order. This suggests that the materials surface is an important
contributor to charge carrier loss.
