**2. Synthesis of nano-crystalline perovskites**

There are many proposed methods for synthesis of PNSs by many groups in the literatures. Here we would like to express five of most common and essential methods (**Figure 1**) [21–23].

## **2.1 Solvent-induced precipitation**

The physical properties of perovskite cluster such as size of NPs can be arranged by using long alkyl chain amine derivatives while oleic acid ensures the colloid stability via preventing the aggregation. In order to initiate the solvent-induced precipitation, and obtain colloidal MAPbBr3 NPs, lead bromide (PbBr2) and methyl ammonium bromide (CH3NH3Br) were mixed with Octylammoniumbromide (OABr) in acetone with oleic acid (OAc) and octylamine and the solution were kept at 80°C. The PLQY of obtained NPSs was about 20% as well as stable over three months. After this first attempt, PLQY of NPSs was increased up to 83% by optimization of the molar ratios of starting materials [22, 24].

**51**

**Figure 2.**

*Ref. [26]).*

*Perovskite Nanoparticles*

(OA<sup>+</sup>

formation [28–30].

**2.3 Hot injection method**

*DOI: http://dx.doi.org/10.5772/intechopen.94588*

**2.2 Ligand assisted reprecipitation (LARP) technique**

processed, stable core–shell-type Methyl ammonium (MA<sup>+</sup>

In this method, a polar solvent such as dimethylformamide (DMF) which dissolve all starting materials and capping ligands have been used to prepare the precursor solution [25, 26]. This solution is added dropwise into vigorously stirred toluene which is not a good solvent for starting materials and perovskite crystal. Zhang et al. has demonstrated the synthesis of colour- tuneable PNSs (average particle size of 3.3 ± 0.7 nm) with a PLQYs of 50–70% (**Figure 2**) [25]. It was claimed that a slight descending of PLQY was observed by the ascending of the size of the perovskite crystal (2–8 μm, PLQY < 0.1%). In the nanometer scales, surface defects of the crystals can easily be passivated by ligands. Thus, most of the photo-generated charges can recombine before there are trapped by defects on the surface. However, due to the less ligand passivation, the number of defects on the bulk perovskite structure`s surface, which increased the number of trapped charges, are significantly high, resulting very low PLQY. In another study, well-defined cubic and thermally stable FAPbX3 nanocrystals (about 10 m) has been prepared by LARP method. The reported PLQY for the NPS was 75% [27]. A new procedure, which was used to obtain a core-shell shape by using the LARP approach has been recently demonstrated. With this proposed method, a solution-

) lead bromide perovskite NPs (≈5–12 nm) with good PLQY was prepared.

The stability of inorganic perovskites is significantly higher than that of hybrid perovskite crystals. By changing the organic cation with an inorganic one (e.g., Cs),

*(a) Schematic illustration of Set up for LARP; (b) starting materials and shape of perovskite nano-crystals; (c) image of typical solution containing CH3NH3PbBr3 nano-structures (reproduced with permission of* 

In addition to this, Core–shell-type NPs was accomplished by systematically changing the molar ratio of capping ligands, OABr, and MABr without altering total amount of alkylammonium bromide and synthesis conditions. The color tunability of NPs in the blue to green spectral region (438–521 nm), high PLQY, and reasonable stability under ambient condition are credited to the quantum confinement imparted by the crystal engineering associated with core–shell NP

) + Octyl ammonium

#### **Figure 1.**

*Common synthesis methods for perovskite nano-crystals.*

*Perovskite and Piezoelectric Materials*

capping ligands can reduce surface defects in the same way of the traditional NC preparation. Thus, size and shape of PNSs can be tune finely from a single perovskite layer or below the exciton Bohr radius for using the effect to quantum confinement to multilayers which exhibits bulk-like properties. With this method, it is possible to prepare nanostructures like quantum dots (QDs), nanoplatelets

In a simple PNS growth process, the methylammonium cations are embedded in the voids of the corner-sharing PbX6 octahedra, the long alkyl chain cations only at the periphery of the octahedra with their chains hanging it. Therefore, long alkylammonium ions can be used as the capping agents to limit the growth of the PNSs in three-dimension (3D). There are five common methods proposed in the literature which exhibits good prospects for obtaining various uniform and defect free PNSs. These are named as solvent-induced precipitation, hot injection, template assisted,

In order to determine the structural and optic properties of PNSs, some characterization techniques such as small angle x-ray scattering (SAXS), scanning electron microscope (SEM), absorption and emission spectroscopy have been used extensively. It is crucial to know the shape and optical response of the nanocrystals

As it is mentioned above, well-defined PNSs were used in many applications such as optical lasing and LEDs. Some of those applications have been investigated intensively by many groups all around the world. Some milestone studies have been

There are many proposed methods for synthesis of PNSs by many groups in the literatures. Here we would like to express five of most common and essential

The physical properties of perovskite cluster such as size of NPs can be arranged

by using long alkyl chain amine derivatives while oleic acid ensures the colloid stability via preventing the aggregation. In order to initiate the solvent-induced precipitation, and obtain colloidal MAPbBr3 NPs, lead bromide (PbBr2) and methyl ammonium bromide (CH3NH3Br) were mixed with Octylammoniumbromide (OABr) in acetone with oleic acid (OAc) and octylamine and the solution were kept at 80°C. The PLQY of obtained NPSs was about 20% as well as stable over three months. After this first attempt, PLQY of NPSs was increased up to 83% by optimi-

(NPLs), nanosheets (NSs), and nanowires (NWs) [19, 20].

ligand assisted reprecipitation and emulsion methods [13, 14].

for the further opto-electronic application of them.

**2. Synthesis of nano-crystalline perovskites**

zation of the molar ratios of starting materials [22, 24].

*Common synthesis methods for perovskite nano-crystals.*

presented comparatively.

methods (**Figure 1**) [21–23].

**2.1 Solvent-induced precipitation**

**50**

**Figure 1.**
