**4.2 Device fabrication methods**

The 2D/3D multidimensional perovskite can be synthesized via many ways: one-step deposition, two-step deposition, anti-solvent method, the self-assembly method, vapor-assisted solution deposition approach [90], etc. In the one-step deposition process, the 2D and 3D precursors are mixed, and the layers are grown simultaneously. In a two-step process, the 3D layer is first deposited then the 2D-perovskite is grown on top of it in a consecutive step. In 2019, Zhang and his co-workers reported a 2D/3D perovskite by post-treated n-butylamine iodide (BAI) and the residual PbI2 on a one-step deposited MAPbI3 film. They added a thin 2D-perovskite layer on the top of the 3D-perovskite and grain boundaries. The formed 2D/3D perovskite has the stability of 2D (after three months the perovskite still support 80% of its initial efficiency) and the high performance of 3D (VOC = 1.09 V, JSC = 22.55 mA/cm2 a, FF =0.74, PCE = 18.3%) [91]. The anti-solvent method has been used as an ordinary recipe for getting a 3D-perovskite film [92]. The anti-solvent (e.g., C.B., toluene, etc.)

**Figure 11.**

*The process of the anti-solvent method. Reprinted with permission from Ref. [40].*

is employed as a second solvent to cause instantaneous nucleation for the 3D film's fast crystallization. When the anti-solvent is used as a solvent for the 2D organic salt, the in-situ 2D growth method can be practically combined with the usual anti-solvent method, as illustrated in **Figure 11**. The anti-solvent containing the organic salt for 2D is directly dripped on the substrate, which is wet with a precursor solution of the 3D-perovskite. The dripping process of the anti-solvent is followed by a one-step process. Toluene containing phenylethylammonium iodide (PEAI) was used as the anti-solvent for a 3D/2D perovskite structure [93].

In the low-pressure vapor assisted solution process, the larger organohalide (PEA) doped with a metal halide (PbI2) is first spin-coated on the substrate and then reacts with the smaller organohalide (MAI) vapor in a low-pressure oven [94].
