Effect of lead thiocyanate ions on performance of tin-based perovskite solar cells

Perovskite solar cells (PSCs) have a high efficiency, and their price is relatively low; thus, they are attracting considerable attention as a substitute for expensive Si solar cells. However, highly efficient PSCs are not ecofriendly, because they contain toxic metals such as Pb. Therefore, we develop Sn-based PSCs to reduce the Pb content. First, 11 different perovskite precursors are synthesized by increasing the amount of Pb(SCN)(2) from 0 to 0.5 M in CH(NH2)(2)SnI3. Then, PSCs are fabricated, and their characteristics are compared. Scanning electron microscopy confirms that the proper amount of Pb(SCN)(2) uniformizes the grain size of the perovskite layer and reduces the amounts of pinholes. The crystallization and optical absorption of each pemvskite layer are confirmed by X-ray diffraction analysis and ultraviolet-visible spectra, and the characteristics of the PSCs are confirmed by the current density-voltage graph. The Sn-based PSCs with 0.25 M Pb(SCN)(2) exhibit a high efficiency of 8.4%, which is significantly higher than that (1.6%) of Sn-based PSCs without Pb(SCN)(2). The calculated Pb concentration of CH3NH3PbI3 is 0.37 g/mL, while that of CH(NH2)(2)SnI3 containing Pb(SCN)(2) is 0.08 g/mL. These results indicate the possibility of producing highly efficient PSCs with reduced lead content.