Dear Huiyu,

I think MAPbI2 is the best behaving perovskite material found till now. It has good optoelectronic properties for solar cell application. It has relatively high dielectric constant, a direct bandgap near the optimum value for the highest conversion efficiency, a high absorption coefficient as Ga AS and better in some wavelengths, high mobility and small effective masses with the electron and hole mobility in the same range enhancing the bipolar conduction, relatively high diffusion length in the order of one micrometer, highest stability compared to the other perovskites,easy to synthesize at produce in thin films at low temperatures. It gave till now PCE photoconvertion efficeincy of more than 20 percent approaching that of single crystal silicon solar cells

There is research efforts to substitute Pb or to mitigate its toxicity by tight encapsulation

of the solar cells and end of life recycling.

For mor information please follow the paper in the link: http://pubs.acs.org/doi/abs/10.1021/acsenergylett.6b00499

Best wishes 

Dear Abdelhalim,

Thank you for your detailed answer.

Best wishes

Dear Huiyu 

Of course you can use another Pb-based salts, not only PbI2 as staring material for CH3NH3PbI3. Some another candidates such as PbCl2, Pb(CH3COO)2, Pb(NO3)... + CH3NH3I you can obtain the final perovskite film.  CH3NH3PbI3 is special material with excellent optoelectronic proprieties. At this moment only this compounds CH3NH3PbI3  gives high power conversion efficiencies with relatively easy processable technique for low cost solar cells. 

Regards

LC

Dear Ludmila, thank you for your answer. It is clear that CH3NH3PbI3 is a very good PV material. I was curious why CH3NH3PbI3 is so good for PV from the view of materials science. To me, its advantages include diect semiconductor, proper band gap, defect-tolerant, ease to fabricate, low cost. But there are huge amount of materials including natural and artificial compounds, I doubt CH3NH3PbI3 is the only choice. Why not is the community taking the main efforts in looking for another environment-friendly compounds?

That right ! Its take time until the researcher in the field found another excellent material. All of as are looking for new materials.