Improved Power Conversion Efficiency and Stability of Perovskite Solar Cells Induced by Molecular Interaction with Poly(ionic liquid) Additives

Abstract

Ionic liquid (IL) additives proved to have a positive effect on the device efficiency and stability of perovskite solar cells. However, since ILs are small molecules and undergo Coulomb interactions, they can easily aggregate and evaporate over long times, which would cause instabilities during a long-term device operation. To overcome these problems, we polymerize ILs into macromolecules and incorporate them into perovskite films as well as into the corresponding solar cells. Both cations and anions of the used poly­[1-(2-acryloylethyl)-3-methylimidazolium] bis (trifluoromethane) sulfonamides (PAEMI-TFSIs) are designed to coordinate with the Pb and I of PbI6 2– octahedra, respectively, which changes the crystallization behavior of the perovskite films. Importantly, the PAEMI-TFSI efficiently passivates electronic defects on the grain boundaries and thereby enhances the charge-carrier transport in the perovskite film. As a result, PAEMI-TFSI-modified MAPbI3 solar cells show a high power conversion efficiency of 22.4% and an excellent storage stability (92% of the initial efficiency remains after 1200 h operation in a nitrogen atmosphere for nonencapsulated devices).

Surface-anchoring fluorinated sulfonate enables efficient and stable perovskite photovoltaics

“…Interestingly, upon the deposition of TFS-TFMS, the Pb–I peaks were shifted toward higher binding energy, lying at 138.03 and 142.91 eV, which could be attributed to the formation of ionic bonding or Lewis acid–base interaction between uncoordinated Pb 2+ and TFMS − . 41,42 Moreover, the Pb 0 peaks were almost hardly recognized, demonstrating that the unbonded Pb 2+ defects were effectively coordinated by TFS-TFMS molecules. A similar shift of I 3d peaks in Fig.…”