Browsing by Author "Kirchartz, Thomas"

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    Characterizing the influence of charge extraction layers on the performance of triple‐cation perovskite solar cells
    (2023) Siekmann, Johanna; Kulkarni, Ashish; Akel, Samah; Klingebiel, Benjamin; Saliba, Michael; Rau, Uwe; Kirchartz, Thomas
    Selecting suitable charge transport layers and suppressing non-radiative recombination at interfaces with the absorber layer is vital for maximizing the efficiency of halide perovskite solar cells. In this study, high-quality perovskite thin films and devices are fabricated with different fullerene-based electron transport layers and different self-assembled monolayers as hole transport layers. Then, a comparative study of a significant variety of different electrical, optical, and photoemission-based characterization techniques is performed to quantify the properties of the solar cells, individual layers, and, importantly, the interfaces between them. In addition, the limitations and problems of the different measurements, the insights gained by combining different methods, and the different strategies for extracting information from the experimental raw data, are highlighted.
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    A universal strategy of perovskite ink‐substrate interaction to overcome the poor wettability of a self‐assembled monolayer for reproducible perovskite solar cells
    (2023) Kulkarni, Ashish; Sarkar, Ranjini; Akel, Samah; Häser, Maria; Klingebiel, Benjamin; Wuttig, Matthias; Wiegand, Simone; Chakraborty, Sudip; Saliba, Michael; Kirchartz, Thomas
    Perovskite solar cells employing [4-(3,6-dimethyl-9H-carbazol-9-yl)butyl]phosphonic acid (Me-4PACz) self-assembled monolayer as the hole transport layer have been reported to demonstrate a high device efficiency. However, the poor perovskite wetting on Me-4PACz caused by poor perovskite ink interaction with the underlying Me-4PACz presents significant challenges for fabricating efficient perovskite devices. A triple co-solvent system comprising dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and N-methyl-2-pyrrolidone (NMP) is employed to improve the perovskite ink-Me-4PACz coated substrate interaction and obtain a uniform perovskite layer. In comparison to DMF- and DMSO-based inks, the inclusion of NMP shows considerably higher binding energies of the perovskite ink with Me-4PACz as revealed by density-functional theory calculations. With the optimized triple co-solvent ratio, the perovskite devices deliver high power conversion efficiencies of >20%, 19.5%, and ≈18.5% for active areas of 0.16, 0.72, and 1.08 cm2, respectively. Importantly, this perovskite ink-substrate interaction approach is universal and helps in obtaining a uniform layer and high photovoltaic device performance for other perovskite compositions such as MAPbI3, FA1-xMAxPbI3-yBry, and MA-free FA1−xCsxPbI3-yBry.