**6. Conclusions**

Lead is known to damage the nervous system and cause brain disorders. In this direction, a theoretical study carried out by De Angelis and group [137] has replaced Pb by Sn (**Figure 11**) with effective development of the GW method with spin‐orbit coupling to accurately model

**Figure 11.** Pictorial representation of replacement of lead by strontium in perovskite solar cells [138].

and then compared it to the CH3

carried out by Jesper Jacobsson and group [138] has provided deep physical insights into the photophysical nature of a metal‐halogen perovskite by removing lead with strontium, which is relatively nontoxic and inexpensive. CCSD calculations and DFT study were performed on

structures and the optical properties. This is based on the fact that the ionic radii of Sr2+ and Pb2+ are almost identical, so the exchange could be made as it will not affect the crystal struc‐

reported to be around 1.55 eV [5, 42]. The second effect that was caused by shifting Sr for Pb is that the shape of the pdos graphs for both the halogen and the organic ion is shifted and slightly distorted. The lower electronegativity of Sr compared to Pb shifts the electronic cloud closer to the iodine atoms in the lattice, which perturb the local dipole moment as well as the bonding angles between the iodine octahedra and consequently their columbic interaction with the methylammonium dipoles. The charge distribution is similar to the two structures, with higher charge density around lead compared to strontium due to the higher atomic

The Perovskite solar cell (PSC) field has now become an emerging field and reports on fur‐ ther improvement in performance are expected in the near future, achieving PCE of more than 30% efficiency has now become a realistic goal. Furthermore, PSC can be used as top cells in two‐level tandem configurations using crystalline silicon or copper indium gallium

NH3 PbI3

gives a bandgap of 1.6 eV, which is fairly close to the experimental value

and CH3

NH3 PbI3

by the SR‐DFT method. Another study

to extract and compare the electronic

. They predicted that

the properties of CH3

264 Nanostructured Solar Cells

the two basic structures of CH3

NH3 SrI3

MASnI3

ture. CH3

number of lead.

**5. Roadmap**

NH3 SnI3

is a better electron transporter than MAPbI3

NH3 SrI3 The intense appeal of hybrid organic‐inorganic perovskite materials such as solar cells is exceptionally promising. Their enhance optoelectronic properties, deposition techniques, and device structure have led to the higher power conversion efficiencies. Due to the high absorp‐ tion coefficients and panchromatic absorptions of perovskite, they have become ideal materi‐ als for thin film solar cells. However, some complexities as the poor stability in humid air and the toxicity of lead used are a matter of concern. In some perovskite materials, the hysteresis is also pronounced due to the strong dependence of photocurrent to the voltage scan condi‐ tions. Still the exceptional performance of hybrid perovskite materials has created revolution in the field of renewable energy with cheap solar cells. Highly efficient solar cells with record performance are still an important milestone to be achieved. The highly innovative and new elegant designs, deep insights into the photophysics and mechanisms of cell operation should now be the main focus of future research.

Finally, we can conclude that the recent advances with perovskite materials will motivate the researchers to expand their horizons to other inorganic or organic pigments, for which the power of mesoscopic solar‐cell architectures will emerge to offers more promising opportunities.

The author acknowledges the financial assistance by the DST WOS‐A (CS‐1005/2014). The author is also thankful to her mentors Dr. G. Narahari Sastry, Head, Center for Molecular Modeling and Dr. K. Bhanuprakash, Chief Scientist, I& PC division, CSIR‐Indian Institute of Chemical Technology for the useful discussions and suggestions.
