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

Ionic liquid (IL) additives proved to have a positiveeffect onthe device efficiency and stability of perovskite solar cells. However,since ILs are small molecules and undergo Coulomb interactions, theycan easily aggregate and evaporate over long times, which would causeinstabilities during a long-term device operation. To overcome theseproblems, we polymerize ILs into macromolecules and incorporate theminto 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 tocoordinate with the Pb and I of PbI6 (2-) octahedra, respectively, which changes the crystallization behaviorof the perovskite films. Importantly, the PAEMI-TFSI efficiently passivateselectronic defects on the grain boundaries and thereby enhances thecharge-carrier transport in the perovskite film. As a result, PAEMI-TFSI-modifiedMAPbI(3) solar cells show a high power conversion efficiencyof 22.4% and an excellent storage stability (92% of the initial efficiencyremains after 1200 h operation in a nitrogen atmosphere for nonencapsulateddevices).