Solar Cells (SCs) energy-conversion technologies have been widely studied from their physical fundamentals to potential commercial applications. In particular, SCs Fill Factors (FFs) are a key factor ...for evaluating the transport efficiency of the photo-generated current and consequently the potential photovoltaic of the device. However, FF dependence on other solar cell relevant electronic properties is not entirely clear, blearing the physical meaning of this factor. In this context, this work reports the derivation of a self-consistent and generalized analytical equation by using simple Shockley diode equation and Lambert W-function that explicitly relates solar cells FFs with simple key electronic parameters. The photo-generated (JL)-to-reverse saturation (J0) current density ratio (JL/J0) was the key parameter considered for this approach because of its considerable limiting impact on FF magnitude. The accuracy of this equation was tested by an exhaustive contrast with a wide variety of experimental data for different solar cells technologies.
•A generalized equation to estimate solar cells Fill Factors (FFs) was proposed.•Shockley diode model and Lambert W-function were used as theoretical basis.•Photo-generated and reverse saturation currents effects on FFs were considered.•Theoretical approach was contrasted with different solar cells experimental data.•Theoretical FFs were estimated with errors <3% concerning the experimental ones.
•Depth Sensing Indentation (DSI) data analysis procedures were critically discussed.•Uncertainty propagation theory to study different error sources in DSI was used.•Experimental and theoretical ...error sources in DSI data analysis were considered.•The effect of error sources on the sample Young´s modulus uncertainty was studied.•Both error sources can considerably impact on the Young´s modulus uncertainty.
A systematic and critical review about the propagation of uncertainties related to the Depth Sensing Indentation data analysis standard procedures and its effect on the estimation of Young´s modulus of materials is reported. Uncertainties related to experimental issues like calibration of indenter area profile and determination of effective applied force and their propagation in estimating the indenter-sample reduced elastic modulus were discussed. On the other hand, theoretical uncertainties related to the contact mechanics fundamentals used for calculating the Young´s modulus of materials by using experimentally determined reduced elastic modulus in indentation experiments were also discussed. Theoretical uncertainties associated to assume fixed values for the mechanical properties of the indenter (Poisson´s ratio and Young´s modulus) and sample (Poisson´s ratio) to estimate the sample Young´s modulus were studied. In general, all the results suggest the experimental uncertainties are the main source of error in estimating the sample Young´s modulus, however the uncertainties associated to theoretical procedures can be comparable with them in some cases.
We report a systematic study about the thickness and microstructure influence on the mechanical properties of nanocrystalline Cu thin films grown by DC sputtering. Mechanical properties were ...determined by using atomic force microscopy-assisted nanoindentation. Results showed a clear decrease of the elastic modulus and indentation hardness as the film thickness and grain size increase. Annealing time as well as the temperature seem to affect the mechanical behavior of the films by inducing microstructural changes, producing comparable changes to those produced by size effects (film thickness). Results suggest that both effects are important to explain the mechanical behavior of polycrystalline thin films. This work helps understanding what physical mechanisms play a fundamental role on the mechanical behavior of thin films.
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•A novel analysis to study the solids’ energy dissipation capacity was proposed.•Analysis based on Depth-Sensing Indentation (DSI) data was considered.•An equation for the elastic (Ue)-to-total (Ut) ...strain energy ratio is proposed.•Maximum displacement (hm) and plastic hysteresis (hp) were the considered parameters.•Ue/Ut was set in terms of the hp/hm ratio, observing an uncertainty of about 8 %.
In emergent nanotechnology areas like Micro Electro-Mechanical Systems (MEMS) the components capacity to dissipate strain energy is a key factor to evaluate their potential lifespan. In this context, we present the direct derivation of an analytical expression to estimate the elastic–plastic solids energy dissipation capacity from Depth Sensing Indentation (DSI) data. An expression to the fast calculation of the elastic (Ue)-to-total (Ut) strain energy ratios (Ue/Ut) from loading and unloading curves was particularly proposed. Assuming reasonable power law behaviors for these curves this expression allows calculating the strain energy ratios only considering the maximum displacement (hm) and plastic hysteresis (hp), which are experimentally easy to estimate. The simplifications and assumptions taken in this work ensure, in the worst of the cases, Ue/Ut ratios with uncertainties about 8 %. Despite this, the results could represent an interesting improvement in the time spending-to-accuracy relation for estimating these ratios.
Lead selenide (PbSe) thin films deposited by aqueous-based chemical methods have recently reached considerable importance for the production of different low cost and good quality optoelectronic ...devices. Applications in infrared devices as well as in low cost photovoltaic technologies as efficient absorbent layers have been extensively studied. In this work, the synthesis of homogeneous, polycrystalline, low-roughness, electrically conductive and narrow band gap PbSe thin films by using Chemical Bath Deposition (CBD) on glass substrates is reported. The effects of using different NaOH concentrations on the films physical and chemical properties were studied. Structural analysis realized by X-Ray Diffraction (XRD) technique showed the polycrystalline nature of the films, particularly observing a preferred texture. Atomic Force Microscopy (AFM) studies revealed a compact and homogeneous growth of the thin films. A well-defined microstructure and low roughness (varying between 5 and 35 nm) were generally observed. Scanning Electron Microscopy (SEM) imaging studies showed the good growth quality of the thin films, observing well-defined film-to-substrate interfaces. Film thickness values between 138 ± 9 and 277 ± 20 nm were estimated. Chemical composition analysis realized by Energy Dispersive X-Ray Spectroscopy (EDS) exposed the non-stoichiometric nature of the PbSe films. An atomic concentration predominance of Se with respect to Pb in all samples was observed, suggesting a possible p-type conductivity. Infrared spectrophotometry measurements indicated energy band gaps in the Mid-Infrared Range (MIR), estimating values from 0.326 up to 0.393 eV. The thin films generally presented high electrical conductivities with respect to the typical ranges for semiconductors, estimating values in the order of 101 (Ω·cm)−1. Results show that the low cost and simple synthesis CBD based procedures can be used to produce high structural and morphological quality PbSe thin films with attractive optoelectronic properties (narrow band gap and electrically conductive) for the potential development of devices in infrared detection industry.
•Polycrystalline PbSe thin films by simple chemical bath procedure were synthesized.•Influence of NaOH on the films structural and morphological properties was studied.•Films presented high growth quality, being homogeneous, adhesive and low-roughness.•MIR band gaps and exceptional electrical conductivity in the films was observed.•Films properties suggest their potential for application in IR detection devices.
Freestanding thin films of Cu–Al–Ni shape memory alloys (SMAs) have attracted interests in recent years for the development of next generation micro-scaled sensors and actuators in MEMS. Thin films’ ...capacity to recover stress-induced strain is critical to assess their potential for applications in these technologies. In this work, we report for the first time a quantitative study of this capacity in a freestanding Cu–Al–Ni thin film by Atomic Force Microscopy (AFM)-assisted nanoindentation. Stress-induced pseudoelastic (or superelastic) effects were successfully observed by this technique for relatively high strains up to a relative indentation depth of 30% concerning the film thickness. This effect highlights a clear shape memory effect, suggesting a sample's high mechanical performance for potential applications in the design of micro actuators for MEMS technologies. Results enable to set new perspectives of the use of this technique as an efficient methodology for future study of pseudoelasticity in micro/nanostructured SMAs.
•Stress-induced superelasticity was studied in a freestanding Cu–Al–Ni thin film.•Atomic Force Microscopy assisted nanoindentation was used for mechanical testing.•Superelastic (or shape memory) effects were successfully observed by this technique.•These effects were observed for high strains up to 30% concerning film thickness.•Results show the potential of this technique for studying shape memory effects.
In this work, we report a systematic study on the Stopping Power Spectra (SPS) of 4He ions in different metal chalcogenide semiconductors. SPS in II (Zn, Cd) – VI (O, S, Se, Te) and IV (Pb) – VI ...binary semiconductors were studied by using SRIM (2013) simulation software for analyzing the energy dissipation profiles of 4He ions. Ions’ energies from 0.1 to 10 MeV were considered for simulations. Stopping powers were generally estimated between 0.1 and 0.6 keV/nm. Results are particularly useful for analytical data processing in Rutherford Backscattering Spectrometry (RBS) experiments focused on an accurate estimation of the thickness of thin films and multilayer structures based on metal chalcogenide semiconductors.
•Stopping powers (SPs) of 4He ions II-VI and IV-VI semiconductors are reported.•Zn, Cd and Pb-based binary semiconductors were particularly considered.•Elements' SPs were calculated by SIMNRA software using the Bethe-Bloch model.•Compounds' SPs were well modeled by Bragg's rule for high energies (>0.1 MeV).•SPs varied between 0.1 and 0.6 keV/nm for energies between 0.1 and 10 MeV.
A systematic finite element analysis (FEA) of conical indentation in different isotropic elastic-plastic bulk solids was realized. In particular, the relation between the indentation Hardness ...(H)-to-Reduced Elastic Modulus (Er) ratio and the Elastic (Ue)-to-Total (Ut) strain energy ratio was studied. Results showed a linear dependency between both ratios as predicted by analytical studies, being the proportionality constant mainly dependent on cone semi-angle (θ) and material Poisson´s ratio (ν). A well-agreement with experimental data reported in the literature was observed for a wide variety of materials. By a simple analysis of the Oliver & Pharr method and our results, we proposed two analytical equations to calculate the H and Er parameters overcoming the indenter contact area (AC) dependence in indentation data analysis. AC-independent analytical procedures can become interesting to simplify the data analysis and overcome considerable uncertainties due to possible pile-up effects associated with different plastic deformation phenomena.
•A rigorous finite element study of conical indentation in bulk solids was realized.•Different isotropic and homogenous elastic-plastic materials were considered.•A linear relation between the strain energy and H/Er ratios was validated.•Validation by comparing analytical, numerical and experimental data was done.•An area-independent procedure was proposed to estimate the mechanical properties.
Atomic Force Microscopy (AFM)-nanoindentation is one of the most popular techniques for characterizing the nanomaterials' mechanical properties. A good calibration of the indenter area profile is ...essential to achieve quantitatively reliable calculations of these properties. Accurate profile estimation is particularly critical to minimize uncertainties in key mechanical properties like hardness and elastic modulus. In this work, we report the use of indium as a potential candidate for assessing the nanoindenters’ area profiles by imaging analysis of nanoindentation-induced plastic footprints. AFM-nanoindentation technique was particularly used for inducing plastic strain. A systematic and rigorous profiles study was carried out at the apex neighborhood, considering heights lower than 200 nm for an accurate estimation at the nanoscale. Results suggest that this methodology is useful to characterize the indenter real geometry shape at the nanoscale, representing a “fast” and low-cost alternative to other popular imaging methods like those based on electron microscopy techniques.
This research focuses on the study of the growth quality, by means of the chemical profile analysis, of good structural and morphological quality chemical bath deposited PbSe thin films on glass ...substrates (SiO2) by Rutherford Backscattering Spectroscopy (RBS). RBS results with other complementary techniques like XRD and SEM were contrasted. Thin films by using different NaOH concentrations during the growth process were synthesized. XRD studies showed the films polycrystalline nature and their good structural quality. Pure structural effects of amorphous SiO2 and PbSe face-cubic-centered structure were observed. SEM imaging analysis revealed the good morphological growth quality of the PbSe films, observing well-defined films dimensions (thickness), a clear film-to-substrate transition at the interface and good microstructural homogeneity. According to XRD and SEM results, RBS experiments contrasted with theoretical simulations evidenced the good growth quality of the PbSe films. A good agreement between experimental data and theoretical modelling by assuming a simple film/substrate structure with a perfectly defined interface and negligible film roughness for the PbSe/SiO2 samples was achieved. RBS experimental-theoretical analysis reveal the non-stoichiometric nature of the PbSe films, being consequent with preliminary EDS based chemical studies. In particular, a predominance of Se with respect to Pb (considering the atomic concentration) in all samples was observed, suggesting a possible p-type conductivity. By stopping power analysis, thin films thicknesses between 141 and 296 nm were also estimated, being comparable to those obtained from SEM imaging analysis of the samples cross-sections. General results show that some aspects (chemical profile of the structure and interfaces quality) related to the growth quality of the chemical bath deposited PbSe thin films, studied by RBS experiments, are considerably intercorrelated to those analyzed by other techniques like XRD and SEM. This suggests RBS method as a suitable technique for a complete and rigorous analysis of thin films growth quality.
•Homogeneous and adhesive PbSe films were synthesized by chemical bath deposition.•Rutherford Backscattering Spectroscopy (RBS) was used to study the films growth quality.•RBS revealed the good growth quality, which was supported by XRD and SEM studies.•Samples presented well-defined film-to-substrate interfaces and low roughness.•Results suggest RBS as a suitable technique to analyze the films growth quality.
