**2.3 Hot injection method**

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),

#### **Figure 2.**

*(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 Ref. [26]).*

#### *Perovskite and Piezoelectric Materials*

chemical and thermal stability of Perovskite material can be increased greatly (**Figure 3**) [31, 32]. It is possible to obtain various crystal phases by changing the temperature resulting a shifting in the optical responses. The hot injection method is a widespread method for synthesizing inorganic PNSs. In a typical synthesis procedure, a solution of PbX2 (X = I/Br/Cl), in octadecene (ODE) along with oleic acid and oleyl amine is prepared. During stirring, Cs-oleate is injected into that solution quickly under dry condition at 140–200°C [32]. To quench the reaction (after 5–10 sec), the reactor is cooled with an ice bath. With this method, it is easy to obtain uniform nanocubes with the size of 4–15 nm edge length representing high PLQY, up to 50–90% and a very narrow emission band (12–42 nm) in the visible region (410–700 nm). As it was mentioned before, the optical properties of the NPSs are related to shape, size,

#### **Figure 3***.*

*Schematic illustration of Hot-injection method (left-hand), image of Cs2SnI6 samples under UV-light (righthand) and possible crystal shapes obtained by hot-injection method (reproduced with permission of Ref. [33]).*

#### **Figure 4.**

*Schematic illustration of perovskite nano-crystal preparation by the template-assisted method (reproduced with permission of Ref. [36]).*

**53**

**Figure 5.**

*Perovskite Nanoparticles*

perovskites.

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

**2.4 Template-assisted method**

applications such as lasers [36, 37].

**2.5 Emulsion method**

capping agent.

and surface chemistry of them due to the significant changes in the band structures. Therefore, by the variation of the surfactants, ligands, reaction temperature and time, the perovskite precursor composition can be adjust [33] to realize the formation of nanowires, nanoplatelets, spherical dots, and nanorods (**Figure 3**) [33–35]. A critical point for the hot injection is the reaction temperature effecting the size of the NPSs. To overcome this disadvantage, new methods have been developed for hybrid

In this synthesis approach, NP formation is induced by a specific substrate such as mesoporous silica and aluminum oxide film as a template [36–38]. NPSs is obtained on the films which exhibits intensive light. This technique is suitable for formation of mono disperse NPSs with various narrow emissions (full wind of half maximum (FWHM) is less than 40 nm) bands from green (FWHM: 22 nm) to near infrared (FWHM: 36 nm) by template optimization [37–39]. In a recent study, perovskite nanocrystals have been prepared in a nano-porous structure. By this kind of strategies, it is possible to confine PNSs (<10 nm) without any capping agents (**Figure 4**). In other words, the emission wavelength of perovskite nanoparticles can be arranged precisely for sophisticated photonic

In order to control the crystallization of perovskite and obtain uniform NPs, emulsion synthesis method was modified [40]. By using this method, it is possible to tune the size of PNSs under 10 nm with an PLQY up to 92% [41]. In this method, an emulsion is prepared with two immiscible solvents. After that, a demulsifier is added into this for initiating solvent mixing and start crystallization (**Figure 5**). For this procedure, DMF and n-hexane are very good candidates as immiscible solvents while tert-butanol or acetone is used as demulsifier solvent [41]. This method is suitable to obtain PNSs in solid state which can be used in another solvent matrix for an application later. Furthermore, long alkyl ammonium halides are used as

*(a) Schematic illustration of preparation of nano-crystals by emulsion method; (b) ternary phase diagram (DMF/OA/n-hexane); (c) image of a typical CH3NH3PbBr3 emulsion, colloidal NP solution and solid-state* 

*powder of CH3NH3PbBr3 NPs (reproduced with permission of Ref. [41]).*

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

*Perovskite and Piezoelectric Materials*

chemical and thermal stability of Perovskite material can be increased greatly (**Figure 3**) [31, 32]. It is possible to obtain various crystal phases by changing the temperature resulting a shifting in the optical responses. The hot injection method is a widespread method for synthesizing inorganic PNSs. In a typical synthesis procedure, a solution of PbX2 (X = I/Br/Cl), in octadecene (ODE) along with oleic acid and oleyl amine is prepared. During stirring, Cs-oleate is injected into that solution quickly under dry condition at 140–200°C [32]. To quench the reaction (after 5–10 sec), the reactor is cooled with an ice bath. With this method, it is easy to obtain uniform nanocubes with the size of 4–15 nm edge length representing high PLQY, up to 50–90% and a very narrow emission band (12–42 nm) in the visible region (410–700 nm). As it was mentioned before, the optical properties of the NPSs are related to shape, size,

*Schematic illustration of Hot-injection method (left-hand), image of Cs2SnI6 samples under UV-light (righthand) and possible crystal shapes obtained by hot-injection method (reproduced with permission of Ref. [33]).*

*Schematic illustration of perovskite nano-crystal preparation by the template-assisted method (reproduced* 

**52**

**Figure 4.**

*with permission of Ref. [36]).*

**Figure 3***.*

and surface chemistry of them due to the significant changes in the band structures. Therefore, by the variation of the surfactants, ligands, reaction temperature and time, the perovskite precursor composition can be adjust [33] to realize the formation of nanowires, nanoplatelets, spherical dots, and nanorods (**Figure 3**) [33–35]. A critical point for the hot injection is the reaction temperature effecting the size of the NPSs. To overcome this disadvantage, new methods have been developed for hybrid perovskites.
