High performance wide-bandgap perovskite and semi-transparent solar cells manufactured by Flash Infrared Annealing

Single-junction and multi-junction (tandem) perovskite solar cells represent in today’s photovoltaic (PV) field one of the most investigated technologies. The promising results reached during the past two decades led to efficiencies up to 26.1 % for single-junction and up to 33.7 % for perovskite/silicon tandem solar cells, higher than the widely diffused single-junction silicon solar cells. Nevertheless, the market share of PV is still dominated by the well-established silicon technology since organic-inorganic perovskites are sensitive to atmospheric environmental conditions such as exposure to moisture. The lab-scale perovskite processing methods typically employed are challenging to scale up and not environmentally friendly due, among other reasons, to the high amount of harmful solutions they exploit. In this scenario, Flash InfraRed Annealing (FIRA) represents a promising alternative to avoid toxic solvents and prolonged annealing times incurring high energy consumption. This photonic annealing method enables the crystallization of pinhole-free perovskite thin films with an irradiation time of less than 1 second and yields single-junction solar cell efficiencies of up to 20%. The goal of this thesis work is to realize an efficient and stable wide-bandgap perovskite solar cell for multi-junction devices using FIRA processing. To carry out the envisioned project, the composition of the deposited organic-inorganic hybrid perovskite thin films was adjusted to achieve an optimal optical bandgap and obtain devices with satisfactory performance. Different anionic and cationic stoichiometries were tested in the solution precursor to identify the best candidate to manufacture perovskite halide solar cell devices. The results showed that FIRA could be successfully applied to realize thin films with different iodine-bromine ratios with external quantum efficiency (EQE) comparable to the already optimized FAPbI3 composition. Instead, chlorine-containing films showed a less performant behavior than the iodine-bromine counterpart. Indeed, the presence of chlorine seems to be leading to phase segregation phenomena that hinder the quality of the grown layers. The devices underwent comprehensive characterization using spectroscopy techniques, optical and electron microscopy, morphological surface analyses, and standard solar cell characterization methods such as current-voltage (JV) and EQE measurements. Lastly, the electrode responsible for hole extraction was optically optimized by realizing a highly transparent dielectric/metal/dielectric stack. This optimization allows non-absorbed radiation from the top cell's active area to reach the bottom cell in a multi-junction configuration.