To address the issue of instability and surface defects
in three-dimensional
lead halide perovskite solar cells (PSCs), two-dimensional (2D) pseudo-(quasi)
perovskites, such as Ruddlesden–Popper (RP) and Dion–Jacobson
(DJ) perovskites, have garnered significant attention. Controlling
the orientation of their layered crystallites is key to vertical charge
transport in 2D PSCs; however, their detailed electronic properties
are yet to be fully understood. Herein, we investigated the effect
of processing additives (ammonium salts: NH4Cl, NH4Br, NH4Cl, NH4SCN, and CH3NH3SCN with/without alkali metal salts (NaCl, KCl, RbCl,
and CsCl) in water) on the crystallographic nature and anisotropic
microwave photoconductivity of RP and DJ perovskites. Importantly,
a strong correlation (correlation coefficient, r =
0.882) was observed between the power conversion efficiencies (1–11%)
of inverted PSCs and anisotropic (both out-of-plane and in-plane to
the substrate) photoconductivities for the 34 compositions of additives
analyzed herein. In contrast, the one-dimensional photoconductivity
and crystallographic degree of orientation exhibited significantly
weaker correlations. These results underscore the importance of anisotropic
mobility in 2D PSCs and could serve as guidelines for their further
development.