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Here in this paper, we demonstrate a facile technique for creating the mixed formamidinium (, FA+) and methylammonium (, MA+) cations in the lead iodide perovskite. This technique entails a facile drop-casting of formamidinium iodide (FAI) solutions on as-prepared MAPbI3 perovskite thin films under the controlled conditions, which leads to controllable displacement of the MA+ cations by FA+ cations in the perovskite structure at room temperature. Uniform and controllable mixed organic cation perovskite thin films without a "bi-layered" or graded structure are achieved. By applying this approach to photovoltaic devices, we are able to improve the performances of devices through extending their optical-absorption onset further into the infrared region to enhance solar-light harvesting. Additionally, this work provides a simple and efficient technique to tune the structural, electrical, and optoelectronic properties of the light-harvesting materials for high-performance perovskite solar cells.

Cd1−xMnxTe/CdTe superlattices and thin films were grown by molecular beam epitaxy on GaAs (001) substrates. Spectroscopic ellipsometry measurements were performed on Cd1−xMnxTe/CdTe superlattices with compositions x = 0.4, 0.8, and Cd1−xMnxTe thin films with x = 0.2, 0.4, 0.6 at room temperature in the photon energy range 1.4–5 eV. In superlattices the pseudodielectric functions measured by ellipsometry show specific features related to the exciton transition between quantized interbands. The exciton transitions related to the heavy holes of 11 H, 22 H, and 33 H are observed and identified. In thin films spectroscopic ellipsometry allows the clear identification of the energy gap E0. Additionally, critical point transitions are observable in both the spectra of the superlattices and films. Photoreflectance spectra were also performed at room temperature in order to compare with our ellipsometry results. After taking into account the strain-induced and quantum confinement effects, the theoretical calculations are in good agreement with our experimental spectra. Ellipsometry appears to be a suited technique to monitor the MBE growth, ultimately also in situ, of diluted magnetic low-dimensional systems.

Photoreflectance spectra of MBE grown GaAsAlGaAs MQWs in an intermediate electric field regime are analyzed by using a lineshape model accounting for both bulk and multilayer contributions to the Δ R R signal. The experimental spectra exhibiting the simultaneous presence of both Franz-Keldysh oscillations and quantum confinement related structures in the same spectral energy range (1.4–1.7 eV) were fitted to a lineshape model consisting of a linear combination of a modified version of the Aspnes asymptotic expression for subsidiary oscillations and first derivative functional forms typical of exciton photoreflectance in quasi-bidimensional systems. By comparing the optical data obtained in different surface field conditions it is shown that the proposed analytical procedure allows reliable information on MQW parameters to be obtained even when the spurious signal due to subsidiary oscillations originating in the buffer or substrate, is much greater than the optical response associated with quantum confinement.

In this communication we report on experimental results obtained from the combined use of ellipsometry and photoreflectance to investigate the optical response of typical MQW structures. The motivation for this approach is related to the need for a correct analysis of the lineshape of photoreflectance spectra. Ellipsometric data yield two important contributions about the nature and the degree of localization of the spectral structures in the excitonic region: (a) experimental curves instead of model profiles as starting reflectivity functions for derivations, (b) possible values of oscillator strengths of the transitions investigated. The energies of the main spectral features are compared with the quantized electronic levels obtained in the framework of the effective mass approximation in the envelope function scheme and a discussion of data previously reported in the literature is performed with the help of results obtained by the coupled techniques.

In this work reflectance (R) and thermoreflectance (TR) spectra in the infra-red of bulk P and B heavily doped silicon samples are reported and discussed. The values of the scattering time and of the effective mass, as well as the temperature derivative of the plasma frequency, scattering time and high-frequency dielectric constant are extracted from the data and analysed in terms of free-carrier-photon and free-carrier-impurity interaction.

In this paper reflectance (R) and thermoreflectance (TR) spectra in heavily doped silicon concerning both interband and intraband transitions are reported and discussed. The heavily doped sample shows a red-shift and lifetime broadening in the two singularities E1(similar 3.4eV) and E2(similar 4.5eV). The values of the scattering time τ extracted from the reflectivity fit are obtained and compared with those obtained from Hall mobility measurements.

Boron‐doped polycrystalline silicon samples containing variable amounts of iron have been investigated by means of transmission measurements, from 230 to 360 cm−1, in order to study the effect of the presence of iron on boron acceptor excitation spectrum lines. The first absorption measurements in the far infrared which indicate the formation of Fe‐B complexes and the accumulation of Fe at the grain boundaries in such samples are reported here.