**Author details**

*Perovskite and Piezoelectric Materials*

Although reaction (3) is reversible at just 80–85°C, methylammonium iodide decomposes into more volatile compounds as represented by reactions (4) and (5):

It was found that HI(g) and CH3NH2(g) were dominant products during the decomposition of MAPbI3 and only trace amounts of CH3I and NH3 were found. Though, the ratio of CH3I and NH3 increased at higher temperature and lesser than HI(g) and CH3NH2(g). In short, HI(g) and CH3NH2(g) were the dominant decomposition products at ambient temperature under vacuum while CH3I and NH3 gases were obtained at high temperature. Both processes occurred simultaneously near ambient temperature in vacuum and the later was favored at high temperature. To find out the decomposition temperature of perovskites, Thermogravimetric analysis (TGA) was used. From the mass loss of TGA curve for MAPbI3, the decomposition onset temperature was found to be 234°C [62]. This indicates that as the practical application temperature usually is less than 100°C, so this high decomposition temperature made the stability of MAPbI3 not a big issue. The as prepared film did not show any changes in XRD patterns when stayed inside the vacuum for up to three days. This might be owing to the purer perovskite films without any exposure to the ambient atmosphere. Though, the commonly degradation of the perovskite solar cell was apparent even with encapsulation. This could be inadequate to estimate the long-term stability of a photovoltaic material, which is essential to work for a long time at temperatures lower than the decomposition temperature [72]. The fact that inert condition and encapsulation cannot completely avoid MAPbI3 perovskite degradation. At low temperature, the degradation of MAPbBr3 was found by only releasing HBr and CH3NH2 gases [69]. The encapsulation of devices is essential not only to prevent exposure to oxygen and moisture, but also to avoid leakage of volatile decomposition products. Photostability can also be increased by

replacing MA cation with more stable Cs/FA combination. Substituting organic cations with inorganic Cs<sup>+</sup>

to stabilize perovskite solar cells [73, 74]. Grancini et al. [74] stated an ultra-stable 2D/3D (HOOC(CH2)4NH3)2PbI4/CH3NH3PbI3 perovskite, presenting a PCE of 12.9% with carbon electrodes and 14.6% with the normal mesoporous structure and

By introducing n-butylammonium iodide (BAI) to MAPbI3 perovskite, a mixed 2D (BA)2PbI4 structure is formed, which probably provide an improved protection for the 3D perovskite against heat stress [75]. Octylammonium (OA) cation has also been reported to enhance the thermal stability of perovskites and keep 80% of their initial efficiency for 760 h aged at 85°C in ambient atmosphere without encapsulation [76]. Other additives, such as π-conjugated polymer, nonvolatile ionic liquids, bifunctional hydroxylamine hydrochloride guanidinium isothiocyanate, have also been reported to improve the thermal stability of various perovskites [77–79].

The discovery and development of organic inorganic perovskite materials have become a hot research topic in the field of photovoltaics. This chapter deals with a comprehensive discussion on the properties and applications of organic inorganic perovskites materials in PSCs. The extraordinarily outstanding performances of organic inorganic perovskites result of their excellent properties. Solar cells based

CH NH I CH I NH 33 3 3 → + (5)

CH NH I CH NH HI 33 32 → + (6)

or Rb+

cations is also valuable

**84**

stability of one-year.

**5. Conclusion and perspective**

Madeeha Aslam, Tahira Mahmood\* and Abdul Naeem National Centre of Excellence in Physical Chemistry, University of Peshawar, Peshawar, Pakistan

\*Address all correspondence to: tahiramahmood@uop.edu.pk

© 2020 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
