La₂O₃ interface modification of mesoporous TiO₂ nanostructures enabling highly efficient perovskite solar cells

Perovskite solar cell performance is critically dependent on the characteristics of the electron transporting layer (ETL) and its interface. This work demonstrates the importance of interface modification in which the charge transport kinetics is improved through band gap engineering of the interfaces in perovskite solar cells with La₂O₃. The surface of a mesoporous TiO₂ ETL (mp-TiO₂) on CH₃NH₃PbI₃-based solar cells is modified using a simple dip-coating method involving a lanthanum salt solution. The layer thickness of La₂O₃ was optimized, and its effects on the conduction band position, interfacial charge recombination, and photovoltaic performance were investigated. Modifying the mp-TiO₂ ETL with La₂O₃ resulted in a nearly 46% enhancement of the power conversion efficiency because of the energetically favourable band gap engineering, which allowed the fast transfer of photo-generated electrons from the perovskite absorber layer to the ETL. Our simple interfacial control approach uses a new efficient interface-modifying material, demonstrating that interface engineering could be a key strategy for improving the performance of perovskite solar cells.