Advanced materials for down-shifting of solar energy in perovskite photovoltaic cells

This thesis presents a study of lanthanide complexes as luminescent materials for performing down-shifting of UV radiation and improving the performance of perovskite solar cells (PSCs), enhancing their efficiency and photostability. Perovskite solar cells are a new and promising class of solar cells, and allow for high power conversion efficiency. However, PSCs present challenges related to long-term stability and degradation such as under UV radiation. Additionally, PSCs are not capable to absorb the whole solar spectrum: for example they are not capable to absorb UV photons; this limits their photovoltaic conversion efficiency. Down-shifting (DS) systems made of organo-lanthanide complexes represent a possible strategy to address these issues by converting UV radiation into longer wavelength radiation. The luminescent materials are embedded into a polymer matrix, creating a planar down-shifting film that is then applied to the front surface of the cells. In this study, DS films were synthesized using europium and samarium complexes embedded into a poly(methyl methacrylate) polymer matrix. The DS films were first characterized photophysically, applied to silicon solar cells (c-Si) and to PSCs with a FACs active layer, and then the integrated devices were optoelectronically characterized. Measurements of absorption, reflectance, and transmittance, of absolute photoluminescence quantum yield, and photoluminescence spectroscopy allowed for estimating the optical properties of the lanthanides complexes. Then, measurements of external quantum efficiency and current-voltage characteristics on the integrated devices quantified the impact of down-shifting on both silicon solar cells and FACs PSCs. The results have shown that DS films have great potential to enhance the efficiency of the cells. The measurements on the integrated device are encouraging and have highlighted the main relevant parameters for optimizing the coupling of down-shifting systems with solar cells.