First-Principles Investigation of the TiO2/Organohalide Perovskites Interface: The Role of Interfacial Chlorine.

We investigate the prototypical interface between organohalide perovskites and TiO2 by first-principles electronic structure calculations. The investigated heterointerface is representative of conventional dye-sensitized solar cells based on a mesoporous TiO2 scaffold and of flat devices in which a compact TiO2 film is used as electron selective layer. We find that the MAPbI3 and MAPbI3-xClx perovskites tend to grow in (110)-oriented films on TiO2, due to the better structural matching between rows of adjacent perovskite surface halides and TiO2 undercoordinated titanium atoms. Interfacial chlorine atoms further stabilize the (110) surface, due to an enhanced binding energy. We find that the stronger interaction of MAPbI3-xClx with TiO2 modifies the interface electronic structure, leading to a stronger interfacial coupling and to a slight TiO2 conduction band energy upshift. Our modeling study may constitute the basis for a further exploitation of perovskite solar cells.