**Acknowledgements**

*Solar Cells - Theory, Materials and Recent Advances*

anti-solvent for a 3D/2D perovskite structure [93].

PEDOT:PSS/PEAxMA1xPb0.5Sn0.5I3/PC61BM/PEI/Ag) [96].

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

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

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

**4.3 Applications in regular or inverted structure perovskite solar cells**

Planer structures are always employed, n-i-p standard structure and p-i-n inverted structure. The researchers used 2D/3D perovskite in these two structures as follows: In 2019, Abbas and his co-workers [95] developed a way to add a 2D-layered perovskite with MAPbI3 bulk 3D-perovskite by a vertically oriented 2D-layered mixed with a bulk 3D-perovskite they select the anilinium ion as the sizeable organic cation. In this research, they used a normal n-i-p structure and recorded an efficiency up to 16%. The planar solar cell heterojunction with ITO/ PEDOT-PSS/perovskite/PCBM/BCP/Ag was fabricated [95]. In 2020, Jia Zhang and Bin Hu recorded a 15.93% efficiency with 2D/3D Pb-Sn alloyed perovskite. They applied the inverted structure p-i-n on their work with the solar cell structure (ITO/

Multi-dimensional 2D/3D hybrid perovskites have proven to be one of the most promising approaches to improving PCE and stability than pure 3D PSCs. Many novel 2D-perovskites can be synthesized in terms of materials engineering and consistent unknown properties studied. Besides, the recently proposed computational theoretical study would speed up selecting and applying 2D materials. In particular, long-chain alkyl cations seem to be suitable for stabilizing perovskite materials based on 2D-Pb-Sn or Sn. The performance can be improved by technical composition and structure. Besides, it remains essential to study the mechanism of

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oven [94].

**Figure 11.**

**5. Conclusion**

The authors acknowledge Science and Technology Development Fund (STDF) and (CMRDI) for their support to this study through the project grant no. 25250 in Egypt.
