engleski

Optimisation of the electron transport layers in lead-free perovskite solar cells

Modern multi-layer perovskite solar cells repose on the active layer between two charge transfer layers ; the electron transfer layer (ETL) and the hole transfer layer (HTL). For the ETL layers semiconducting metal oxides are commonly used, such as zinc oxide, titanium oxide or tin oxide. Among them titania is widely established, zincite is a viable alternative and tin oxide is substantially underrated. All these can be derived relatively easy, furthermore zincite can be chemically derived at room temperature conditions. Further upgrading the ETLs by reaching out to nanolevel by means of nanostructured thin films can further improve the efficiency of solar cells. Even though the zincite nanorods ETLs are tailored to increase specific surface area and facilitate a vectorised electron path towards the electrodes, only a limited increase of efficiency is evidenced due to considerable recombination. In addition to that a thermally induced degradation occurs on the boundary of zincite and the active perovskite layer. This can be overcome by using a methyl ammonium cation free lead perovskite. In this work we prepared perovskite solar cells. For ETL film ordered array of zincite nanorods were employed. Standard (lead-based) MAI-FAI (methylammonium and formamidinium iodide) perovskite and just FAI perovskite were used for photoabsorbers. The solar cells were prepared in protective atmosphere on conductive glass substrates, with gold electrode on the other side, and were characterized immediately upon fabrication using electrical (current-voltage cycles and external quantum efficiency), structural (grazing incidence X-ray diffraction) and morphological (electron microscopy) characterisation. By removing the MAI cation from the active layer overall better fill factors and lower hysteresis rates were achieved. The solar cells based on MAI free perovskite also showed improved stability upon atmosphere exposure. Further work will focus on optimizing the zincite nanorod thin films to understand fully the effect of synthesis on the solar cell performance.

zinc oxide, 1D nanostructures, solar cells

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