The interaction between hybrid organic–inorganic halide perovskite and selective contacts in perovskite solar cells: an infrared spectroscopy study

Abstract

The interaction of hybrid organic–inorganic halide perovskite and selective contacts is crucial to get efficient, stable and hysteresis-free perovskite-based solar cells. In this report, we analyze the vibrational properties of methylammonium lead halide perovskites deposited on different substrates by infrared absorption (IR) measurements (4000–500 cm⁻¹). The materials employed as substrates are not only characterized by different chemical natures (TiO₂, ZnO and Al₂O₃), but also by different morphologies. For all of them, we have investigated the influence of these substrate properties on perovskite formation and its degradation by humidity. The effect of selective-hole contact (Spiro-OmeTad and P3HT) layers on the degradation rate by moisture has also been studied. Our IR results reveal the existence of a strong interaction between perovskite and all ZnO materials considered, evidenced by a shift of the peaks related to the N–H vibrational modes. The interaction even induces a morphological change in ZnO nanoparticles after perovskite deposition, pointing to an acid–base reaction that takes place through the NH₃⁺ groups of the methylammonium cation. Our IR and X-ray diffraction results also indicate that this specific interaction favors perovskite decomposition and PbI₂ formation for ZnO/perovskite films subjected to humid conditions. Although no interaction is observed for TiO₂, Al₂O₃, and the hole selective contact, the morphology and chemical nature of both contacts appear to play an important role in the rate of degradation upon exposure to moisture.