*2.3.3 Thermal annealing*

In hot-casting technique, Yang et al. described the Volmer-Weber growth mechanism for the creation of island-like grains and the transition to a compact perovskite film. Thermodynamic energy is important in accelerating perovskite crystallisation and precursor diffusion, which directly affects the film shape (**Figure 2b**) [46].

Thermal energy can lower the surface tension between the precursor solution and the substrate, increasing the probability of large grain domain with fewer surface defects. As the temperature rises, isolated like grains get larger and begin to form bonds with one another, finally generating a high-quality perovskite film with no pinholes. Thermal annealing not only increases material transport inside the film and facilitates solvent evaporation, it also improves charge extraction in the active layer [47]. Through


#### **Table 2.**

*Photovoltaic parameters of various hot-casted PSCs.*

#### *Thin Film Solution Processable Perovskite Solar Cell DOI: http://dx.doi.org/10.5772/intechopen.106056*

quick solvent removal, flash infrared annealing (FIRA) can enhance the development and crystallisation of perovskite films. In comparison to the traditional thermal annealing, short heating pulses, compared to traditional thermal annealing, can greatly minimise the deterioration of organic components, even at extremely high temperatures [48]. The grain size distribution along the periphery of the perovskite film made by hot casting is greater than the core size distribution, and the particle size distribution is annular, as proposed by Ren et al. During the evaporation of the solvent, a compensatory flow from the centre of the solution to the edge is thought to occur spontaneously, resulting in a greater concentration and larger particle size near the edges.

### **2.4 Precursor chemistry**
