Project Details
Projekt
Two-dimensional perovskites: from fundamental understanding to their application at interfaces in perovskite solar cells (2D-FASOL)
Subject Area
Experimental Condensed Matter Physics
Term
since 2022
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 506699365
Halide perovskites have revolutionized the field of thin film solar cells with a remarkable increase in performance yielding efficiencies that are on par with single crystalline silicon. Aside from the perovskite material itself, interfaces to charge transport layers critically influence not only the overall performance but also the device stability. Recently, two dimensional (2D) perovskites have gained more and more attention as a strategy to tailor the interfaces in devices. They have turned out to be a key to unlock high efficiencies and improved stability in perovskite solar cells, in particular when employed at the interface between the photoactive 3D perovskite and the charge transport layers. The reasons for these improvements are a subject of a vigorous ongoing debate and a clear understanding of the nature of these 2D/3D interfaces is still in its infancy.In this project, we will start off with a systematic investigation of pure 2D perovskites and study changes in their electronic structure, optical properties, and their stability depending of the choice and size of the bulky A-site cation. In comparison to their 3D analogues, their ability to form stable interfaces with charge transport materialswill be studied in detail. This is particularly important, as no research on the chemical interaction between 2D perovskites and metal-oxides has been published so far. Next, 2D perovskites will be integrated as thin layers on top and/or below an optimized 3D perovskite absorber material. Detailed analysis of these heterostructures will allow us to unravel how these bulky cations and the specific processing parameters affect the formation, electronic structure, and dimensionality of the respective interlayer. The insights gained from these fundamental studies will be correlated to the electrical characteristics of unipolar (hole-only; electron only) devices based on 2D/3D perovskite interfaces. Ultimately, the most promising combinations of 2D and 3D perovskites will be integrated in solar cells. We are in particular interested in comparing the open circuit voltage with the quasi Fermi level splitting to understand the contribution of parasitic recombination and limited charge extraction to the overall losses in device performance. This will help to clarify whether the presence of 2D interfacial layers can suppress recombination that would otherwise occur if the 3D material is in direct contact with other charge transport layers, such as fullerenes, metal-oxides, etc. Aside from shelf-life under various conditions (inert, ambient, heat), the operational stability of pure and mixed-halide systems is of paramount interest. In the latter systems, we will directly study the impact of 2D/3D interfaces to potentially mitigate the notorious halide segregation. The fundamental understanding that will be gained in this project will be indispensable for further substantial improvements of efficiency and long-term stability of perovskite solar cells.
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