Determination of the complex refractive index and optical bandgap of CH3NH3PbI3 thin films

Abstract

We report the complex refractive index of methylammonium lead iodide (CH 3 NH 3 PbI 3) perovskite thin films obtained by means of variable angle spectroscopic ellipsometry and transmittance/reflectance spectrophotometry in the wavelength range of 190 nm to 2500 nm. Film thickness and roughness layer thickness are determined by minimizing a global unbiased estimator in the region where the spectrophotometry and ellipsometry spectra overlap. We then determine the optical bandgap and Urbach energy from the absorption coefficient, by means of a fundamental absorption model based on band fluctuations in direct semiconductors. This model merges both the Urbach tail and the absorption edge regions in a single equation. In this way, we increase the fitting region and extend the conventional (α ω) 2-plot method to obtain accurate bandgap values.

High-Energy Optical Transitions and Optical Constants of CH3NH3PbI3 Measured by Spectroscopic Ellipsometry and Spectrophotometry

“…The transition energies obtained from The three transitions E C0 , E C1 and E C2 are commonly identified, 8,37,41 however, E C3 and E C4 are not often observed or remarked on. Our obtained value for the bandgap is similar to those previously determined, 10,11,41,46 which has been attributed to a direct transition at the R symmetry point of the Brillouin zone. 38, and 6.97 eV for thin films.…”

“…Guerra and colleagues also observed the transitions at ∼ 4.6 and 5.8 eV via SE but did not measure spectrophotometry data beyond 5 eV. 46 In all the above studies, the highest energy optical transition is not investigated via spectrophotometry measurements in addition to SE.…”

Optical characterization and bandgap engineering of flat and wrinkle-textured FA0.83Cs0.17Pb(I1–xBrx)3 perovskite thin films

“…This is done by the typical Bruggeman effective medium approximation (EMA), with a void fraction of 50%. [5][6][7][8][9]13 As film and roughness layer thicknesses are not known beforehand, they are determined by minimizing the total error obtained from Eq. (2) for all wavelengths, as a function of d f and d r (see Eq.…”

“…Organic-inorganic hybrid perovskite materials are currently one of the most promising materials for next generation solar cells [1][2][3][4][5][6][7][8][9][10] and other optoelectronic devices, 3,4 owing to their high cell efficiencies, high absorption, direct bandgap, long carrier diffusion length, bandgap tunability and low manufacturing costs. [1][2][3][4][5][6][7]10 The use of cesium mixed-cation lead mixed-halide perovskites (FA 1 − y Cs y Pb(I 1 − x Br x ) 3 ) has also significantly improved upon the stability issues of classical PV perovskites like MAPbI 3 .…”

“…[1][2][3][4][5][6][7]10 The use of cesium mixed-cation lead mixed-halide perovskites (FA 1 − y Cs y Pb(I 1 − x Br x ) 3 ) has also significantly improved upon the stability issues of classical PV perovskites like MAPbI 3 . 1,7,10 As such they hold great potential for single junction cells and especially for dual junction Si-perovskite tandem cells.…”