<p>Hybrid
organic-inorganic perovskites have attracted immense interest as a promising
material for the next-generation solar cells; however, issues regarding
long-term stability still require further study. Here, we develop automated
experimental workflow based on combinatorial synthesis and rapid throughput
characterization to explore long-term stability of these materials in ambient
conditions, and apply it to four model perovskite systems: MA<sub>x</sub>FA<sub>y</sub>Cs<sub>1-x-y</sub>PbBr<sub>3</sub>,
MA<sub>x</sub>FA<sub>y</sub>Cs<sub>1-x-y</sub>PbI<sub>3</sub>, (Cs<sub>x</sub>FA<sub>y</sub>MA<sub>1-x-y</sub>Pb(Br<sub>x+y</sub>I<sub>1-x-y</sub>)<sub>3</sub>)
and (Cs<sub>x</sub>MA<sub>y</sub>FA<sub>1-x-y</sub>Pb(I<sub>x+y</sub>Br<sub>1-x-y</sub>)<sub>3</sub>).
We also develop a machine learning-based workflow to quantify the evolution of
each system as a function of composition based on overall changes in
photoluminescence spectra, as well as specific peak positions and intensities. We
find the
stability dependence on composition to
be extremely non-uniform within the composition space, suggesting the presence
of potential preferential compositional regions. This proposed workflow
is universal and can be applied to other perovskite systems and
solution-processable materials. Furthermore, incorporation of experimental
optimization methods, e.g., those based on Gaussian Processes, will enable the
transition from combinatorial synthesis to guide materials research and
optimization.</p>