Deciphering Structure and Charge Carrier Behavior in Reduced‐Dimensional Perovskites

Reduced-dimensional perovskites (RDPs) have advanced perovskite optoelec-
tronic devices due to their tunable energy landscape, structure, and orientation.
However, the origin of structural and photophysical property changes
when moving from low-dimensional to high-dimensional RDPs remains to
be understood. This study systematically reveals structural and photophysical
properties of slot-die-coated Dion-Jacobson (DJ) and Ruddlesden-Popper
(RP) RDPs with different dimensionalities. RP RDPs with lower dimensionality
(n = 2) exhibit a dominant n = 2 phase, preferential out-of-plane orientation,
and longer charge carrier lifetime compared with DJ RDPs. In addition, the
formation kinetics of RDPs with higher dimensionality (n = 4) are unraveled by
in situ X-ray scattering, showing the favorable formation of the lower-n phase
in RP RDPs. The formation of these lower-n phases is thermodynamically
and stoichiometrically favored, while these phases are likely in the form
of an “intermediate phase” which bridges the 3D-like and lower-n phases in
DJ RDPs. DJ RDPs with higher dimensionality demonstrate comparable phase
purity, preferential orientation, spatially vertical phase homogeneity, and longer
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charge carrier lifetime. As such, DJ-based perovskite solar cells (PSCs) (n = 4)
demonstrate better photostability under operational conditions than RP-based
PSCs. Thus, the work paves the way for the utilization of RDPs to upscale PSCs.