Elucidating the Role of Chlorine in Perovskite Solar Cells
It has been proposed that introducing chlorine anion in CH3NH3PbI3 perovskite material can substantially improve material property as well as solar cell performance. To elucidate the role of chlorine in perovskite solar cells (PSCs), here we introduced PbCl2 in the precursor, and studied chlorine configuration evolution during perovskite film formation and associated influence on PSC performances in detail. We found out that chlorine could be successfully incorporated into the precursor film in the form of PbICl or PbCl2 through a properly designed preparation, and it was reserved in the final perovskite film with the configuration of MAPbCl3, PbICl or PbCl2 depending on the fabrication process. However, no evidence of MAPbI3-xClx phase was observed, it is considered that MAPbI3-xClx might be metastable or possesses higher formation energy. In addition, we demonstrate that the formation of porous PbICl scaffold in the precursor film plays a key role in high quality perovskite films realization benefiting from an effective stress release during structure expansion after methylammonium iodide dripping. Moreover, we propose that residual amorphous PbCl2 can effectively passivate defects in perovskite film, and dramatically improve film electrical properties. Finally, n-i-p type planar PSCs with efficiencies up to 19.45% were achieved. It should be mentioned that the whole process for the PSCs with less 100 °C is beneficial for a wide range of applications, such as flexible and tandem solar cells.