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    Hybrid perovskite degradation from an optical perspective: a spectroscopic ellipsometry study from the deep ultraviolet to the middle infrared
    (Wiley, 2021-11-21)
    A quantitative analysis of the thermally induced degradation of various device‐relevant multi‐cation hybrid perovskite films is performed using spectroscopic ellipsometry, for temperatures between 80 and 120 °C. The studied compositions are a triple cation perovskite Cs0.05(MA0.17FA0.83)0.95Pb(Br0.17I0.83)3, a Rb‐containing variant Rb0.05Cs0.05(MA0.17FA0.83)0.90Pb(Br0.17I0.83)3, and a methylammonium‐free Rb0.05Cs0.10FA0.85PbI3 composition. A very wide combined spectral range of 200 nm to 25 μm is covered by combining the data from two separate instruments. The relative changes in organic cation concentrations are quantified from the middle infrared molecular absorption bands, leveraging the use of point‐by‐point fitting for increased sensitivity. Additionally, the formation of PbI2 and non‐perovskite δ‐CsPbI3 phases is evidenced from Bruggemann effective medium fits to the visible and ultraviolet complex refractive indices. Methylammonium is almost completely depleted from the relevant compositions within 100 to 285 min of thermal annealing. The MA‐free perovskite degrades faster at intermediate temperatures, which is attributed to phase instability due to the formation of δ‐CsPbI3 in addition to PbI2.
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    Optical Simulations of Nanotextured All-Perovskite Tandem Solar Cells
    (John Wiley and Sons Inc, 2025-01-01)
    This numerical study investigates, how textures at various locations of all-perovskite tandem solar cells affect their optical performance. For this, hexagonal sinusoidal textures with 750 nm period and aspect ratios (height-to-period) of 27% (moderate) and 54% (pronounced) are considered. The optical simulations are performed with the finite element method and an algorithm to correct for the thick glass superstrate. The complex refractive index data of the wide-bandgap (WBG) and narrow-bandgap (NBG) perovskites with spectroscopic ellipsometry is determined. Texturing between the glass superstrate and the WBG perovskite top cell has an antireflective effect across the whole wavelength region. In contrast, texturing between the WBG perovskite top cell and the NBG perovskite bottom cell has no additional effect for a moderate texture but leads to light trapping in the NBG perovskite for a pronounced texture. Moderate texturing between the NBG perovskite absorber and the metal back contact leads to light trapping in the NBG perovskite but also excites surface plasmons in the copper back contact. Dielectric interlayers between the NBG perovskite and the metal back contact can reduce the plasmonic absorption losses. Texturing potentially allows to increase the current-matched short-circuit current density beyond 17 mA (Formula presented.).
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