Implications of TiO2 surface functionalization on polycrystalline mixed halide perovskite films and photovoltaic devices

Abstract

We exploit TiO₂ surface functionalization as a tool to induce the crystallization process of CH₃NH₃PbI_3−xCl_x perovskite thin films resulting in a reduction of the degree of orientation of the (110) crystallographic planes. Notably, the variation of the film crystalline orientational order does not affect the photovoltaic performances of the perovskite-based devices, whose efficiency remains mostly unchanged. Our findings suggest that other factors are more significant in determining the device efficiency, such as the non-homogenous coverage of the TiO₂ surface causing charge recombination at the organic/TiO₂ interface, defect distribution on the perovskite bulk and at the interfaces, and transport in the organic or TiO₂ layer. This observation represents a step towards the comprehension of the perovskite film peculiarities influencing the photovoltaic efficiency for high performance devices.