Since the inception
of organic–inorganic hybrid perovskites
of ABX
3
stoichiometry in 2009, there has been enormous
progress in envisaging efficient solar cell materials throughout the
world, from both the theoretical and experimental perspectives. Despite
achieving 25.5% efficiency, hybrid halide perovskites are still facing
two main challenges: toxicity due to the presence of lead and device stability. Two particular families
with A
3
B
2
X
9
and A
2
MM′X
6
stoichiometries have emerged to address these two prime concerns,
which have restrained the advancement of solar energy harvesting.
Several investigations, both experimental and theoretical, are being
conducted to explore the holy-grail materials, which could be optimum
for not only efficient but also stable and nontoxic photovoltaics
technology. However, the trade-off among stability, efficiency, and
toxicity in such solar energy materials is yet to be completely resolved,
which requires a systematic overview of A
3
B
2
X
9
- and A
2
MM′X
6
-based solar
cell materials. Therefore, in this timely and relevant perspective,
we have focused on these two particular promising families of perovskite
materials. We have portrayed a roadmap projecting the recent advancements
from both theoretical and experimental perspectives for these two
exciting and promising solar energy material families while amalgamating
our critical viewpoint with a future outlook.