optical constants of thin films

They are positive constants such that 4C-B2 > 0. Variable angle spectroscopic ellipsometry (VASE) is measured at five angles (43.9°, 48.9°, 53.9°, 58.9°, and 63.9°) to obtain the complex optical constants of the present CsPbI3 thin films. = ) As shown in Figure 2a,b, it can be seen from two SEM images taken at two locations of the same sample that the thicknesses are quite different. . a) Schematic diagram of the present sample structure (not to scale). Figure 3a shows a schematic of a perovskite thin film of nonuniform thickness on a glass substrate (note that here the drawing of nonuniform thickness is not scalable and just is used for a model illustration). B Six terms were used in the Forouhi–Bloomer equations for crystalline materials to fit the data and achieve the results. ) To test the accuracy of the theory presented here, a film with the following properties is postulated. The size of beam spot was ≈200 μm in diameter. i The diffraction peaks at 14.34°, 20.68°, 22.98°, 24.07°, 25.18°, 28.94°, 32.35°, and 35.92° correspond to (110), (020), (120), (121), (022), (220), (130), and (132) planes of the γ‐CsPbI3 perovskite. The symbol h represents Planck’s constant and c, the speed of light in vacuum. greatly thanks the Yiguang Instrument Co. of China for providing ellipsometric measurements and technical support. We do not guarantee individual replies due to extremely high volume of correspondence. + + Every term in the sum has its own values of the parameters A, B, C, Eg, as well as its own values of B0 and C0. Thin gold films are key components of modern micro- and nanoscale optical and optoelectronic devices. n Ellipsometry measured a change in polarization as light reflected from the sample of CsPbI3 thin film. 2 Ref. The measured thin film thickness and surface roughness of the CsPbI3 thin film through the cross‐sectional SEM and surface atomic force microscope (AFM) are shown in Figure 2. Often a blanket area on the trench sample with the film of interest is present for the measurement. orcid.org/http://orcid.org/0000-0002-6364-3471, I have read and accept the Wiley Online Library Terms and Conditions of Use. Science X Daily and the Weekly Email Newsletter are free features that allow you to receive your favorite sci-tech news updates in your email inbox. + The five parameters A, B, C, Eg, and n(∞) each have physical significance. As a result, the experimental complex optical constants of the CsPbI3 thin film were obtained in the wavelength range of 300–1200 nm. g C − This polarization change was represented as an amplitude ratio, Ψ, and the phase difference, Δ. Indium tin oxide (ITO) is a conducting material with the unusual property that it is transparent, so it is widely used in the flat panel display industry. Together, n and k are often referred to as the “optical constants” of a material (though they are not constants since their values depend on photon energy). ) The three fitting parameters are An (dimensionless), En (eV), and Brn (eV), where the three parameters are used for the WVASE fitting. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. This rapidly heats up the gold causing it to melt and eventually transform into vapor. It is found that the complex optical constants exhibit a good agreement with the results from the Yiguang measurement (the variation is less than 3%), as shown in Figure S1, Supporting Information. E In the simplest case, this entails depositing the film on two different substrates and then simultaneously analyzing the results using the Forouhi–Bloomer dispersion equations. Through the use of a Tauc plot, the optical bandgap can be estimated from the plotting of (Ahv)2 versus photon energy (hv), as shown in Figure 1c, where the present CsPbI3 perovskite thin film exhibits a direct bandgap at 1.738 eV. This work was partly carried out with support of the Karlsruhe Nano Micro Facility (KNMF) at Karlsruhe Institute of Technology (KIT).   The measurable quantities, R(λ) and T(λ) depend not only on n(λ) and k(λ) of the film, but also on film thickness, t, and n(λ) and k(λ) of the substrate.   C The power conversion efficiency (PCE) of the organic–inorganic hybrid perovskite solar cells (PSCs) based on lead halides progressed rapidly from 3.8% in 2009 to 24.2% in 2019.1, 2 In recent years, all‐inorganic perovskite thin films for solar cells have attracted great attention due to significantly improved stability compared with organic‐containing perovskites.3-5 Although the PCE of all‐inorganic perovskite solar cells lags somewhat behind, excellent progress is being made with the best devices reaching 18% PCE.6-10, Among all‐inorganic perovskite solar cells, those based on CsPbI3 perovskite (α, β, or γ phases) thin films are particularly attractive due to the optical bandgap lying in the range of 1.68–1.73 eV.11-17 This means that CsPbI3 perovskite thin films are well suited for the development of ultrahigh‐efficiency tandem cells, whereby a perovskite top cell is partnered together with a low‐bandgap (≈1.1 eV) solar cell such as crystalline silicon (c‐Si). 1 The measured UV–vis absorbance spectrum and photoluminescence (PL) spectrum of the CsPbI3 thin film are shown in Figure 1b. "Provided that you maintain a high vacuum, heat the metal appropriately, and otherwise follow the procedure, this technique yields films of arbitrary thickness, which is determined by the evaporation time. − . The n and k spectra of such materials can be obtained in accordance with the methodology described in this section for thin film measurements. A and Terms of Use. As expected, the k(λ) spectrum of ITO is zero in the visible wavelength range, since ITO is transparent. The n(λ) and k(λ) spectra of each film are obtained along with film thickness, over a wide range of wavelengths from deep ultraviolet to near infrared wavelengths (190–1000 nm). + Substrate refractive index S= 1.51 (constant) Film thickness d= 1000 nm Film refractive index 3 x io5 n=- + 2.6 d2 Film absorption coefficient 1.5 x lo6 8 (a in nm-I). B.S.R. i The present results of the complex optical constants can be used to help developing high‐performance the CsPbI3 perovskite‐based optoelectronic devices including high‐efficiency CsPbI3/c‐Si tandem solar cells through design and simulation. Figure 1d shows CsPbI3 surface profile across the ellipometry measurement region, where the shown scan length is 3000 μm (note that the size of beam spot is in a diameter of 200 μm). + c) The measured and fitted psi (Ψ) at the five angles of 43.9°, 48.9°, 53.9°, 58.9°, and 63.9°. The Forouhi–Bloomer dispersion equations describe how photons of varying energies interact with thin films. Before performing such tasks, however, knowledge of complex optical constants of CsPbI3 perovskite thin films is mandatory. signal, Regulating the reactivity of black phosphorous through protective chemistry. i 2 [ The reflectance and transmittance of ITO deposited on the same glass substrate were then measured simultaneously, and analyzed using the Forouhi–Bloomer equations. . Enter your email address below and we will send you your username, If the address matches an existing account you will receive an email with instructions to retrieve your username. As a material transitions toward crystallinity, the broad maximum gives way to several sharper peaks in its n(λ) and k(λ) spectra, as demonstrated in the graphics. Complex optical constants of the CsPbBr3 thin film were measured by spectroscopic ellipsometry and modeled by Tauc–Lorentz formulation with seven oscillators. Iga=-- i" 1216 thanks the financial support from the German Research Foundation (DFG) (Ref. and you may need to create a new Wiley Online Library account. The resulting optical constants can be used in optical simulations to explore different photovoltaic device designs based on CsPbI3 absorbers. ) An AFM (Bruker Dimension Icon) was used to investigate surface roughness of the sample. B

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