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

Abstract

Agradecimientos:Agradezco a Cienciactiva y al Consejo Nacional de Ciencia y Tecnología (CONCYTEC) por financiar este trabajo en el marco de una beca completa de maestría (233-2015-1). Reconozco adicionalmente a la Oficina de Internacionalización de la PUCP, y al Servicio de Intercambio Alemán (DAAD) en conjunción con el Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT), por facilitar y financiar dos pasantías a Alemania, las cuales fueron vitales para la producción de este trabajo. A su vez, extiendo mi gratitud al Dr. Jan Amaru Palomino Töfflinger y Dr. Jorge Andrés Guerra Torres, del lado peruano, y al Dr. Lars Korte, Dr. Bernd Stannowski, Dr. Steve Albrecht y Prof. Dr. Bernd Rech, del lado alemán, por hacer posibles mis visitas y trabajos en el Helmholtz-Zentrum Berlin (HZB), así como a Lukas Kegelmann y al Dr. Steffen Braunger por su labor en los trabajos realizados. Finalmente reitero mi agradecimiento al Dr. Jorge Andrés Guerra Torres por su fuerte apoyo y guía en cada etapa de este trabajo. Resumen:Los índices de refracción complejos de películas delgadas de perovskitas de haluros mixtos de formamidinio-cesio de plomo (FA0.83Cs0.17Pb(I1 − xBrx)3), con composiciones variando de x = 0 a 0.4, y para topografías planas y de textura rugosa, son reportadas. Las películas se caracterizan por medio de una combinación de elipsometría espectral de ángulo variable y transmitancia espectral en el rango de longitudes de onda de 190 nm a 850 nm. Las constantes ópticas, espesores de las películas y las capas de microrugosidad, son determinadas con un método "punto a punto", minimizando una función de error global, sin hacer uso de modelos de dispersión, e incluyendo información topográfica proporcionada por un microscopio confocal láser. Para evaluar el potencial de ingeniería del ancho de banda del material, sus anchos de banda y energías de Urbach son determinadas con exactitud haciendo uso de un modelo de fluctuaciones de banda para semiconductores directos. Este considera las colas de Urbach y la región de absorción banda a banda fundamental en una sola ecuación. Con esta información, la composición que brindaría el ancho de banda óptimo de 1.75 eV para una celda solar tándem Siperovskita es determinada. Abstract:The complex refractive indices of formamidinium cesium lead mixed-halide (FA0.83Cs0.17Pb(I1 − xBrx)3) perovskite thin films of compositions ranging from x = 0 to 0.4, with both flat and wrinkle-textured surface topographies, are reported. Films are characterized using a combination of variable angle spectroscopic ellipsometry and spectral transmittance in the wavelength range of 190 nm to 850 nm. Optical constants, film thicknesses and roughness layers are obtained point-by-point by minimizing a global error function, without using optical dispersion models, and including topographical information supplied by a laser confocal microscope. To evaluate the bandgap engineering potential of the material, the optical bandgaps and Urbach energies are then accurately determined by applying a band flu...

Multimodal Microscale Imaging of Textured Perovskite–Silicon Tandem Solar Cells

“…The optical parameters for this perovskite are from ref ( 43 ), and a table of their values is listed as Table S1 ( Supporting Information ). In the simulation, only the perovskite and Si materials were included, as the hole and electron transport materials are much thinner than the photon wavelength of interest and do not strongly absorb in this part of the electromagnetic spectrum and are therefore negligible.…”

CsxFA1–xPb(I1–yBry)3 Perovskite Compositions: the Appearance of Wrinkled Morphology and its Impact on Solar Cell Performance

“…Most recently we reported on the investigation of optical constants and band gaps of flat and wrinkled Cs 0.17 FA 0.83 Pb(I 1-x Br x ) 3 perovskite layers with x = 0-0.4 by variable angle spectroscopic ellipsometry and spectral transmittance. 39 That work and the present study were conducted simultaneously to a study on the appearance of wrinkles in Cs 0. 17 Figure 1a.…”

High-performance wide bandgap perovskite solar cells fabricated in ambient high-humidity conditions

“…As suggested in the literature, the wrinkled-shaped structures are a consequence of compact stress during the film formation, depending on the precursor solution, antisolvent washing and annealing step [53][54][55]. Although the wrinkled surface morphology does not significantly affect the optical properties of the films, the device performance was reduced mainly due to the less conformal deposition of the hole transport layer [49,56]. As shown in SI (Figure S3), higher x leads to relatively deeper cracks in the films, which causes higher density of recombination centers, short-circuits and overall loss in the PSCs' performance [57].…”

“…where α is the absorption coefficient, α 0 is a fitting constant and E U is the Urbach energy. The calculated E U values (see Table 1) are inversely proportional to the Br content, indicating that the crystallinity properties were enhanced with Br ratio (x) [49]. As x increases the Urbach tail energy (attributed to lattice disorder) decreases [49], thus lower values of E U correspond to higher order in the crystal structure.…”

“…The calculated E U values (see Table 1) are inversely proportional to the Br content, indicating that the crystallinity properties were enhanced with Br ratio (x) [49]. As x increases the Urbach tail energy (attributed to lattice disorder) decreases [49], thus lower values of E U correspond to higher order in the crystal structure. The Urbach values attained for our ambient-deposited perovskite films are slightly higher than those of stateof-the-art perovskites deposited under glovebox controlled environment [17], and this leads to relatively higher open-circuit voltage deficit as analysed in SI (Figure S4).…”