Advancing Halide Perovskite Solar Cell by Functional Interlayers

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Halide perovskite based solar cells (PSCs) mark a critical turning point for emerging photovoltaic technologies. The French-German project ALSATIAN aims at enhancing the reliability of PSCs by developing new functional thin-film coatings that will improve stability of high efficiency cells. Rapid efficiency-focused progress in PSCs risks pursuing only a particular device heterostructure which may in fact be nonideal in terms of reliability. ALSATIAN will look beyond standard interlayer materials to focus on novel thin-film materials and deposition procedures to process interlayers by atomic layer deposition (ALD) and molecular layer deposition (MLD) adjacent to the perovskite absorber in the cell to serve as transport, recombination, or passivation layer. Using in situ and operando techniques, we plan to assess the impact of the interface between functional interlayer and perovskite on the device performance and stability. A major objective is to evaluate the compatibility of the interlayer deposition process and the interlayer itself with the perovskite film, since chemical reactions can initiate rapid degradation or create defect sites that impede device functionality. However, for a stabilized interface system the functional layer can provide protection of the perovskite film and improve optoelectronic properties. Hence, we will employ advanced spectroscopic tools paired with DFT calculations to investigate chemical reaction pathways that occur during layer growth at the interfaces. In addition, we will study (photo-)electrochemical reactions between the layers that could be induced under operating conditions in various chemical environments. To this end, we will assess buried interfaces by hard X-ray photoemission and determine key electronic properties, which we will correlate to data from spatially resolved optical spectroscopy. In combination, we will investigate the impact of the interface between the functional thin-film coating and perovskite layer on the device performance and stability in-situ, i.e., in between growth steps, or operando, i.e., for operating solar cells in adapted device architectures.