**4. Mixed 2D/3D perovskites**

Downsides of 2D-perovskites can be reduced by mixing 2D with the ordinary 3D-perovskites to form 2D/3D perovskite. 2D/3D designing intends to combine the advantages of 3D-perovskite (high optoelectronic properties) and 2D-perovskite (high stability) [88] to produce an efficient and stable perovskite material that could contribute to the advancement of PSCs towards commercial industrialization. So, owing to these reasons, the 2D/3D perovskite attracted the researcher's attention during the last few years [89].

#### **4.1 Optoelectronic properties**

The 2D/3D, in comparison to 2D-perovskite, has higher charge mobility, less non-radiative charge recombination, smaller bandgap as illustrated in **Figure 10**, higher power conversion efficiency, long-term stability, and in some cases, do not even need encapsulation.

**175**

*Mixed 2D-3D Halide Perovskite Solar Cells DOI: http://dx.doi.org/10.5772/intechopen.97684*

the best efficiency (η =15.3%).

*Reprinted with permission from Ref. [89].*

**Figure 10.**

**4.2 Device fabrication methods**

parameters (as the 2D/3D perovskite gets closer to 3D). Moreover, 2D in 2D/3D can work as a capping layer to protect the 3D layer from air, moisture, heat; It serves as a hydrophobic encapsulation layer. In 2014, Karunadasa et al. introduced the mixed dimensional perovskite in the PSCs for the first time [77]. In this work [77], a mixture of phenylethylammonium (PEA) and MA cations was prepared to obtain a Ruddlesden–Popper structure of (PEA)2(MA)2[Pb3I10] at (n = 3) with an achieved efficiency of 4.73% [77]. The bandgap of the corresponding 2D and 3D-perovskite was 2.10, and 1.63 eV, respectively. After that, Sargent et al. investigated the efficiency and stability of (PEA)2(MA)*n* − 1[Pb*n*I3*n* + 1] perovskites with higher n (*n* = 6, 10, 40, 60, and ∞) [78], the stability of this 2D/3D perovskites was improved compared to the 3D equivalents. The encapsulated device with lower value of n (i.e., closer to 2D) has the highest stability, but the devices with n < 40 have poor performances due to the lower carrier mobility and high radiative recombination losses. For perovskites with (n < 10), a wider bandgap and lower carrier transport lead to inferior performances. On the other hand, the perovskite with (n = 60) recorded

*A schematic illustrates the effect of increasing the dimensionality on the bandgap and the binding energy.* 

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

=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.)

a, FF

The number of inorganic layers (n) affects the performance parameters of 2D/3D perovskite. The higher the (n) number, the better the performance

#### **Figure 10.**

*Solar Cells - Theory, Materials and Recent Advances*

the obtained XRD spectra corresponding to in-plane and out-of-plane orientations. In contrast, (111) and (222) reflections were noticed for n = 3 and n = 4 quasi 2D-perovskite films (110) and (220) analogously for n = ∞, which implies the vertical growth orientation (n = 3, 4), increasing towards 3D-perovskite; The preferential layer alignment vanished because few BA cations doped in 3D-perovskite and no influence on orientations **(Figure 9)** [65]. From (SEM, GIWAXS) it was concluded that the hot-cast films grew along certain orientations, confirmed by the most remarkable reflections of (111) and (202) planes. The inorganic crystal plates <(MA)n − 1PbnI3n + 1 > 2− are perpendicular to the substrate, forming continuous charge transfer channels favorable to charge transport for optoelectronic applica-

*The generalized concept of the Q.W. morphology in both PEA-based and BA-based spin-cast films. Reprinted* 

Downsides of 2D-perovskites can be reduced by mixing 2D with the ordinary 3D-perovskites to form 2D/3D perovskite. 2D/3D designing intends to combine the advantages of 3D-perovskite (high optoelectronic properties) and 2D-perovskite (high stability) [88] to produce an efficient and stable perovskite material that could contribute to the advancement of PSCs towards commercial industrialization. So, owing to these reasons, the 2D/3D perovskite attracted the researcher's attention

The 2D/3D, in comparison to 2D-perovskite, has higher charge mobility, less non-radiative charge recombination, smaller bandgap as illustrated in **Figure 10**, higher power conversion efficiency, long-term stability, and in some cases, do not

The number of inorganic layers (n) affects the performance parameters of 2D/3D perovskite. The higher the (n) number, the better the performance

**174**

tions [66].

**Figure 9.**

*with permission from Ref. [87].*

**4. Mixed 2D/3D perovskites**

during the last few years [89].

**4.1 Optoelectronic properties**

even need encapsulation.

*A schematic illustrates the effect of increasing the dimensionality on the bandgap and the binding energy. Reprinted with permission from Ref. [89].*

parameters (as the 2D/3D perovskite gets closer to 3D). Moreover, 2D in 2D/3D can work as a capping layer to protect the 3D layer from air, moisture, heat; It serves as a hydrophobic encapsulation layer. In 2014, Karunadasa et al. introduced the mixed dimensional perovskite in the PSCs for the first time [77]. In this work [77], a mixture of phenylethylammonium (PEA) and MA cations was prepared to obtain a Ruddlesden–Popper structure of (PEA)2(MA)2[Pb3I10] at (n = 3) with an achieved efficiency of 4.73% [77]. The bandgap of the corresponding 2D and 3D-perovskite was 2.10, and 1.63 eV, respectively. After that, Sargent et al. investigated the efficiency and stability of (PEA)2(MA)*n* − 1[Pb*n*I3*n* + 1] perovskites with higher n (*n* = 6, 10, 40, 60, and ∞) [78], the stability of this 2D/3D perovskites was improved compared to the 3D equivalents. The encapsulated device with lower value of n (i.e., closer to 2D) has the highest stability, but the devices with n < 40 have poor performances due to the lower carrier mobility and high radiative recombination losses. For perovskites with (n < 10), a wider bandgap and lower carrier transport lead to inferior performances. On the other hand, the perovskite with (n = 60) recorded the best efficiency (η =15.3%).
