Speaker
Description
Photovoltaics play a central role in climate change mitigation. Perovskite solar cells are a promising future technology with respect to sustainability and scalability towards the terawatt scale. Current research is focusing on long-term stability and their application in tandem solar cells.
Low dimensional perovskites (LDPs) are being investigated as surface passivation and charge blocking layers for stable perovskite solar cells. LDPs consist of alternating organic cation layers between inorganic perovskite-like slabs. The former are hydrophobic and prevent moisture-induced degradation enhancing the long-term stability. LDPs also show great promise as high-bandgap perovskite photoabsorbers for tandem solar cells. The high bandgap arises from quantum confinement effects rather than from the mixing of halides, thereby minimizing the risk of phase separation. One of the biggest remaining challenges is the control of the orientation and dimensionality n (i.e. thickness of inorganic slabs between the organic cations) of LDPs. Especially low-n LDPs preferably orientate themselves parallel to the substrate, hindering charge transport and limiting the performance of the solar cell.
In this work, we fabricated thin film perovskite samples and characterized them using spectral and spatial photoluminescence, UV-Vis and XRD. We present two approaches for controlling the dimensionality and orientation of LDPs, respectively: By adding lead iodide to the LDP precursor and selecting a poorly-dissolving solvent, it was possible to adjust the stoichiometry and thus the dimensionality of the LDP passivation layer on top of the 3D perovskite substrate.
In pure LPD absorbers with a high bandgap for application in all-perovskite tandem solar cells, the preferred orientation was changed from horizontal to vertical by employing partial halide substitution, which leads to a compressed unit cell and induced crystal growth in the desired direction.
