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Through the analysis of scales on the drift–diffusion device model of a planar-structured perovskite solar cell, we have obtained accurate-analytical expressions that capture the recombination losses within the cell. The recombination losses are resolved into the radiative and Shockley–Read–Hall mechanisms, as well as interfacial recombination between the perovskite and electron/hole-transporting layers. After parameter calibration with the state of the art planar perovskite solar cell of 23.5% efficiency, the percentage contribution of various recombination loss channels within a planar-structured perovskite solar cell is analytically determined through derived scales and numerically verified at the condition of an open-circuit voltage and a short-circuit current, as well as gives a good prediction of a dominant recombination mechanism within the cell. On this basis, a comparison of loss analysis between the estimated scales and numeric results is carried out at the condition of an open-circuit voltage when a wide range of parameters influencing the recombination current is deviated simultaneously, and a good agreement is obtained. [ABSTRACT FROM AUTHOR]

Meso-structured perovskite solar cells (PSC), utilizing a mesoporous absorber layer consisting of mesoporous metal oxide and the perovskite material inside, are still delivering the highest solar cell efficiency for perovskite-based solar cells up to date. Their outstanding performance critically depends on the nanoscopic morphology formed inside the mesoporous absorber layer. This, however, is not accounted for in most of the perovskite device models, as they are based on an effective-medium formulation for the mesoporous absorber layer, and the details of its underlying morphology are ignored. The mesoporous absorber layer is treated as a two-phase model that describes intrinsic solar cell physics such as free charge carrier generation, carrier transport, and recombination within the two phases, as well as at the interface between the two phases. We derive a spatially smoothed device model for meso-structured PSCs based on volume-averaging of electric potential and electron and hole concentrations of the two-phase model, and this spatially smoothed formulation captures two essential morphological descriptors that are not found in existing effective-medium formulations for meso-structured PSCs, namely, surface-to-volume ratio and porosity inside the mesoporous layer. Furthermore, we determine the explicit functional forms of the effective parameters in the spatially smoothed model for the case of an ideal "Spaghetti" blend morphology. [ABSTRACT FROM AUTHOR]

A mathematical model for meso-structured perovskite solar cells is derived and calibrated towards measured intensity dependent current-voltage characteristics. This steady-state device model describes the transport of free carriers, carrier recombination and optical generation. The optical part considers internal transmission, reflection, and absorption of light, using a transfer matrix approach. The carrier recombination in the form of radiative, Auger and Shockley-Read-Hall mechanisms is accounted for inside the perovskite capping layer, as well as interfacial recombination between the perovskite and electron/hole-transporting layers. After calibration by best-fitting the unknown parameters towards intensity dependent current-voltage measurements of an in-house fabricated meso-structured perovskite solar cell, we identify the dominant recombination mechanisms and their locations inside the cell. A subsequent loss analysis indicates that, in our fabricated solar cell, the interfacial recombination between the perovskite/mesoporous titanium dioxide within the mesoporous absorber layer constitutes the main loss channel. This interfacial recombination accounts for up to 46% of all recombination losses at maximum power, thereby exceeding the recombination inside the perovskite capping layer with 31% loss. Furthermore, the thickness of the perovskite capping layer and the mesoporous layer is varied by means of simulation between 50 and 500 nm, in order to predict the optimum device geometry for the calibrated recombination parameters. [ABSTRACT FROM AUTHOR]

In this paper, strain transfer efficiencies from a single crystalline piezoelectric lead magnesium niobatelead titanate substrate to a GaAs semiconductor membrane bonded on top are investigated using state-of-the-art x-ray diffraction (XRD) techniques and finite-element-method (FEM) simulations. Two different bonding techniques are studied, namely, gold-thermo-compression and polymer-based SU8 bonding. Our results show a much higher strain-transfer for the "soft" SU8 bonding in comparison to the "hard" bonding via gold-thermo-compression. A comparison between the XRD results and FEM simulations allows us to explain this unexpected result with the presence of complex interface structures between the different layers. [ABSTRACT FROM AUTHOR]

Coplanar high-resolution x-ray diffraction is used for the characterization of size, chemical composition, and strain of Ge/Si (001) islands in a three-dimensional island crystal grown using self-assembly on a prepatterned (001) Si substrate. The Ge content in the islands is found to be on the average 40%, while the island shape does not change dramatically during capping.

Lateral composition modulation in InAs/AIAs short-period superlattices was investigated by x-ray grazing-incidence diffraction and coplanar x-ray diffraction at a 'normal' wavelength and at an anomalous wavelength, for which diffraction from the (200) planes does not exhibit a chemical contrast. The experimental data were compared with theoretical simulations assuming that the interfaces consist of a periodic sequence of monoatomic steps.

Research is presented concerning the use of nonspecular and specular x-ray reflectivity to investigate multilayers of SiGe/Si for interface morphology. The techniques used to grow the multilayers are discussed.

A new concept, using a negatively charged tunnel layer as a hole collector, is proposed and theoretically investigated for application in amorphous silicon thin-film solar cells. The concept features a glass/transparent conductive oxide/ultra-thin negatively charged tunnel layer/intrinsic a-Si:H/n-doped a-Si:H/metal structure. The key feature of this so called t+-i-n structure is the introduction of a negatively charged tunnel layer (attracting holes from the intrinsic absorber layer), which substitutes the highly recombination active p-doped a-Si:H layer in a conventional p-i-n configuration. Atomic layer deposited aluminum oxide (ALD AlOx) is suggested as a potential candidate for such a tunnel layer. Using typical ALD AlOx parameters, a 27% relative efficiency increase (i.e., from 9.7% to 12.3%) is predicted theoretically for a single-junction a-Si:H solar cell on a textured superstrate. This prediction is based on parameters that reproduce the experimentally obtained external quantum efficiency and current-voltage characteristics of a conventional processed p-i-n a-Si:H solar cell, reaching 9.7% efficiency and serving as a reference. Subsequently, the p-doped a-Si:H layer is replaced by the tunnel layer (studied by means of numerical device simulation). Using a t+-i-n configuration instead of a conventional p-i-n configuration will not only increase the short-circuit current density (from 14.4 to 14.9 mA/cm2, according to our simulations), it also enhances the open-circuit voltage and the fill factor (from 917mV to 1.0V and from 74% to 83%, respectively). For this concept to work efficiently, a high work function front electrode material or a high interface charge is needed. [ABSTRACT FROM AUTHOR]

The structure and quality of intrinsic hydrogenated amorphous silicon thin films are studied with intended use as passivation layer in heterojunction silicon wafer solar cells. The thin film layers are formed by radio-frequency parallel-plate plasma-enhanced chemical vapor deposition. While the passivation quality of the films is found to improve steadily with increasing deposition temperature, a very narrow process window in terms of pressure variation is observed. The best effective lifetime is obtained at a hydrogen to silane dilution ratio of 1 and a pressure of 66.7 Pa for the used tool configuration. Raman crystallinity and Urbach energy obtained from fitting ellipsometry data confirm that the degradation of the passivation quality outside the process window is due to a phase change into microcrystalline silicon with different growth mechanisms and an increase in bonding related defects. Film growth mechanisms are proposed to account for the observed narrow process window, which are verified by optical emission spectroscopy measurements. [ABSTRACT FROM AUTHOR]

The thermoelectric and physical properties of superlattices consisting of modulation doped Ge quantum wells inside Si1-yGey barriers are presented, which demonstrate enhancements in the thermoelectric figure of merit, ZT, and power factor at room temperature over bulk Ge, Si1-yGey, and Si/Ge superlattice materials. Mobility spectrum analysis along with low temperature measurements indicate that the high power factors are dominated by the high electrical conductivity from the modulation doping. Comparison of the results with modelling using the Boltzmann transport equation with scattering parameters obtained from Monte Carlo techniques indicates that a high threading dislocation density is also limiting the performance. The analysis suggests routes to higher thermoelectric performance at room temperature from Si-based materials that can be fabricated using micro- and nano-fabrication techniques. [ABSTRACT FROM AUTHOR]

Electroplated Cu films exhibit a microstructure evolution at room temperature, called self-annealing. The kinetics of this recrystallization process is strongly influenced by plating conditions in the form of Cu film thickness, current density, and additive content in the electrolyte. Existing models have been used and improved to describe the kinetics of self-annealing. This gives the possibility to evaluate the influence of processing parameters and predict self-annealing behavior of electroplated Cu thin films. [ABSTRACT FROM AUTHOR]

A comprehensive study of the biaxial strain-induced shift of the Si1-xGex Raman active phonon modes is presented. High-resolution Raman measurements of Si1-xGex/Si heterostructures have been compared to x-ray diffraction data. Our approach, unlike previous works, is effective to decouple and quantify separately the effect of strain and composition on the phonon frequencies, yielding an accurate determination of the phonon strain shift coefficients in the entire composition range. Our results show that the strain shift coefficients are independent of the composition, a result which is in good agreement with theoretical calculations, performed within the framework of valence force-field theory. [ABSTRACT FROM AUTHOR]

Lateral composition modulation in InAs/AlAs short-period superlattices was investigated by x-ray grazing-incidence diffraction and coplanar x-ray diffraction at a “normal” wavelength and at an anomalous wavelength, for which diffraction from the (200) planes does not exhibit a chemical contrast. The experimental data were compared with theoretical simulations assuming that the interfaces consist of a periodic sequence of monoatomic steps. The displacement field in the superlattice was calculated by continuum elasticity and using a valence-force field method. From the fit of the experimental data to the theory, the lengths of individual atomic terraces were determined. [ABSTRACT FROM AUTHOR]

We have investigated the structural properties of Si/SiGe electroluiminescent quantum-cascade structures, by means of x-ray reflectivity and diffraction. The cascade structures were grown at a comparatively low temperature of T = 350 °C to avoid misfit dislcoation formation. Despite an overall thickness of the cascade structures of about 9000 Å and Ge contents of up to more than 40% in some of the SiGe wells, the entire stack of layers is indeed pseudomorphic with respect to the Si substrate. The analysis of x-ray reflectivity data yields a rather small rms interface roughness, which increases only slightly from 2 to 2.9 Å from the bottom to the top of the cascade structures. From x-ray reflectivity maps we obtain in addition the vertical and lateral correlation of the interface roughness. It turns out that for long range interface fluctuations the vertical correlation length is larger than for short range fluctuations. [ABSTRACT FROM AUTHOR]

Several high-resolution Raman measurements are conducted to determine the photon strain shift coefficients found in the [Si.sub.1-x][Ge.sub.x] alloys. The results demonstrate that the discussed strain shift coefficients are completely independent of the composition of the heterostructures.

We have investigated the elastic properties of epitaxial MnTe layers using triple axis high resolution x-ray diffraction and reciprocal space mapping. A series CdTe/MnTe superlattices (SLs) grown by molecular beam epitaxy and nearly strain compensated, were deposited on [001] Cd[sub 1 − x]Zn[sub x]Te substrates. In order to obtain the MnTe content of these SLs without an a priori knowledge of the elastic properties of cubic MnTe, annealing experiments were performed to interdiffuse the individual layers into a mixed Cd[sub 1 − x]Mn[sub x] Te alloy layer. For a precise analysis of the data, it was found to be important to determine the in-plane strain of the superlattice layers using reciprocal space maps around symmetric and asymmetric reciprocal lattice points. The value for the Poisson ratio of zinc-blende MnTe was determined to be v = C[sub 11]/2C[sub 12] = 0.77±0.15. [ABSTRACT FROM AUTHOR]