Nanoplasmonic Sensing of CH₃NH₃PbI₃ Perovskite Formation in Mimic of Solar Cell Photoelectrodes

The formation of methylammonium lead iodide (CH₃NH₃PbI₃) perovskite into mesoporous titania (TiO₂) scaffold via a sequential deposition method is known to offer high quality films for good photovoltaic device performance. The growth reactions at the mesoporous TiO₂ film depend on reactants concentration in the host matrix and the reaction activation energy. Here, we have used a NanoPlasmonic Sensing (NPS) approach with gold (Au) nanosensors to monitor the formation of CH₃NH₃PbI₃ perovskite at the lower interface of 350 nm mesoporous TiO₂, typical thickness used in a photovoltaic device. This technique provides time-resolved spectral shifts of the localized surface plasmon resonance at different operating temperatures and methylammonium iodide (CH₃NH₃I₃) concentrations by recording changes in the local vicinity of the Au nanosensors at the mesoporous TiO₂ film interface. Analytical studies included Ellipsometry, Scanning Electron Microscopy, and X-ray diffraction. The results show that perovskite conversion can be obtained at lower CH₃NH₃I₃ concentrations if reaction activation energy is lowered. A significant finding is that the NPS response at 350 nm mesoporous TiO₂ can widely change from red shifts to blue shifts depending on extent of conversion and morphology of perovskite formed at given reaction conditions.