  Phase segregation is a critical phenomenon that influences the stability and
performance of mixed halide perovskite based opto-electronic devices. In
addition to the underlying physical mechanisms, the spatial pattern and
randomness associated with the nanoscale morphology of phase segregation
significantly influence performance degradation a topic which, along with the
multitude of parameter combinations, has remained too complex to address so
far. Given this, with MAPbI1.5Br1.5 as a model system, here we address the
influence of critical factors like the spatial randomness of phase segregation,
influence of ion migration, and the effect of increased non radiative
recombination at material interfaces. Interestingly, our analytical model and
detailed statistical simulations indicate a unique trend morphology evolution
with increased phase segregation results, surprisingly, in a recovery in
efficiency while non-radiative recombination at grain/domain boundaries results
in efficiency degradation. Further, our quantitative and predictive estimates
identify critical parameters for interface states beyond which device
variability could be an important system level bottleneck. Indeed, these
estimates are broadly applicable to systems which undergo phase segregation and
have interesting implications to perovskite based optoelectronic devices from
stability concerns to engineering approaches that attempt to arrest phase
segregation.
