**1.3 CsSnI3-typed perovskite**

With Kanatzidis's group, we introduce p-typed CsSnI3 semiconductor, which is a distorted three-dimensional perovskite structure that crystallizes in the orthorhombic *Pnma* space group at room temperature (RT) (**Figure 1(a)**) [11]. The Sn2+ center sits in a distorted octahedral environment with six I anions, resulting in stereochemically inactive so-called 6s<sup>2</sup> lone pair of electrons. The {SnI6/2} octahedra condense to form a three-dimensional framework via corner-sharing with the Cs+ countercations residing at 12 coordinate interstices within the network made by eight {SnI6/2} octahedra. This structure exhibits direct bandgap properties of 1.3 eV and very high hole mobility of *μ<sup>h</sup>* = 585 cm2 V<sup>1</sup> s <sup>1</sup> with p-type conduction behavior at RT. Thermoelectric power measurements gave positive Seebeck coefficients over the entire temperature range with linear dependence on temperature, suggesting p-type conduction (**Figure 1(b)**). The hole mobility can be estimated from the electrical conductivity using the equation *μ<sup>h</sup>* = *σp*<sup>1</sup> *e* <sup>1</sup> (where *μ<sup>h</sup>* is the hole mobility, *σ* is the electrical conductivity, *p* is the hole concentration, and *e* is the electronic charge). The calculated value is close to that obtained from the Hall effect measurements. Therefore, this compound can be considered as being an excellent candidate material for replacing lead-based perovskite. In 2012, a related inorganic *CsSnI3* perovskite was used as a hole conductor by combining the ruthenium dyes, reaching 8.5% efficiency [12]. From these properties and initial works, the field of p-typed perovskite material has attracted great attention. After these initial works, the field of perovskite-based solar

*Lead-Free Perovskite and Improved Processes and Techniques for Creating Future… DOI: http://dx.doi.org/10.5772/intechopen.106256*

**Figure 1.**

*(a) Distorted three-dimensional perovskite structure of CsSnI3 at RT. red polyhedron, {SnI6/2} : Yellow, Cs. (b) Crystal structure of Cs2SnI6 from the VESTA program. (c) DTA and graphs for Cs2SnI6 for temperature maxima of 400–600°C. reprinted from [8–10].*

cells has literately exploded, with extremely exciting very recent results. CsSnI3 successfully also was demonstrated as light absorber [13]. The high photocurrent densities of more than 22 mAcm<sup>2</sup> can be attained by utilizing CsSnI3 due to its favorable bandgap, optical properties, and low exciton binding energies (BEs) (18 meV) [14]. Nonetheless, an improvement of open-circuit voltage (0.24 V) is still required [15]. Also, the fabrication of tin-based *ASnI3* perovskite cells is highly unstable in the ambient due to the tendency for Sn to get oxidized, and its easy oxidation creates Sn4+ that originates a metal-like behavior in the semiconductor which lowers the photovoltaic performance [5, 16]. Therefore, a clear improvement on the stability remains an objective.
