  Perovskite solar cell (PSC) is one of the most promising next generation
photovoltaic technologies, and there are considerable interests in the role of
possible polarization of organic-inorganic halide perovskites (OIHPs) in
photovoltaic conversion. The polarity of OIHPs, however, is still hotly
debated. In this review, we examine recent literature on the polarity of OIHPs
from both theoretical and experimental points of view, and argue that they can
be both polar and nonpolar, depending on compositions, processing, and
environments. Implications of OIHP polarity to photovoltaic conversion is also
discussed, and effort in answering these questions continues to render us new
insights. In the future, integrating local scanning probe with global
macroscopic measurements in-situ will provide invaluable microscopic insight
into the intriguing macroscopic phenomena, while synchrotron diffractions and
scanning transmission electron microscopy on more stable samples may ultimately
settle the debate.
