Two-dimensional (2D) metal-halide perovskites with alternating cations in the interlayer space (ACI) have demonstrated great potential in photovoltaics. The balance between stability and efficiency could be tailored by varying the distance between the inorganic slabs. However, the efficiencies are still low due to the low carrier mobility and random crystal orientation in the defective ACI films. Furthermore, how the ACI multidimensional perovskites assembled in the solution-processed film is still unclear. Herein, we demonstrated nanoscale hybrid multidimensional (GA)(MA)PbI ACI (guanidinium = GA, methylammonium = MA) perovskite with vertically stacked microcrystals and preferential crystal orientation. In each microcrystal, the low-dimensional ACI are assembled within 3D perovskite nanoscale networks. Such nanoscale heterojunctions prompt ultrafast (~0.3 ps) charge carrier localization from ACI to 3D perovskite and the subsequent efficient charge carrier extraction from the 3D networks to the extraction layers. Based on optimized ACI films, record high-efficiency (>16%) and high-stability planar perovskite cells are achieved. Our results provide new insight into the crystal growth and carrier kinetics of the ACI perovskite solar cells.