  The discovery of lead free all-inorganic alloyed double perovskites have
revolutionized photovoltaic research, showing promising light emitting
efficiency and its tunability. However, detailed studies regarding optical,
exciton, polaron and transport properties remain unexplored. Here, we report a
theoretical study on the variation of carrier-lattice interaction and
optoelectronic properties of pristine as well as alloyed Cs$_2$AgInCl$_6$
double perovskites. We have employed many-body perturbation theory
(G$_0$W$_0$@HSE06) and density functional perturbation theory (DFPT) to compute
exciton binding energy (E$_\textrm{B}$) and exciton lifetime of different
alloyed double perovskites. We find that phonon scattering limits
charge-carrier mobilities and thus, plays an important role in the development
of high-efficiency perovskite photovoltaics. In view of this, dominant
carrier-phonon scattering is observed via Fr\"{o}hlich mechanism near room
temperature. Moreover, we observe a noticeable increase in hole and electron
mobilities on alloying. We believe that our results will be helpful to gain a
better understanding of the optoelectronic properties and lattice dynamics of
these double perovskites.
