Effect of tetrabutylphosphonium iodide as interfacial additive between titanium dioxide and methylammonium lead iodide in mesoscopic perovskite solar cells

Ionic liquids (ILs) are gradually becoming relevant within the efforts towards more stable perovskite solar cells, either by their incorporation into the perovskite active layer or as an interfacial additive. In this work, we synthesized the ionic liquid tetrabutylphosphonium iodide and applied it as an additive at the interface between the electron selective contact - mesoporous - TiO2 and the perovskite CH3NH3PbI3 active layer. Specific conditions of tetrabutylphosphonium iodide (B4PI) interfacial modification resulted in an improved device stability and a reduction of the hysteretic behavior suggesting a possible passivation of trap states and/or mitigation of ionic migration phenomena.