Interfacial charge-transfer engineering by ionic liquid for high performance planar CH₃NH₃PbBr₃ solar cells

The energy barrier at the CH₃NH₃PbBr₃/TiO₂ interface hinders the electron transfer from CH₃NH₃PbBr₃ to compact TiO₂ (cp-TiO₂). Ionic liquid (IL), that forms dipoles pointing away from TiO₂, can adjust the work function of TiO₂ resulting in suitable energy level for charge transfer from CH₃NH₃PbBr₃ to TiO₂. The time-resolved photoluminescence spectroscopy (TRPL) measurements confirm faster electron transfer from the CH₃NH₃PbBr₃ film to TiO₂ after modification by IL. Solar cells based on IL modified cp-TiO₂ demonstrate efficiency of ∼6%, much higher than the devices (0.2%) fabricated using untreated cp-TiO₂ as the electron transport layer.