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Garnet Li7La3Zr2O12 (LLZO) is a promising solid-state electrolyte due to its wide electrochemical stability window and high Li-ion conductivity. This electrolyte has potential to be employed in the form of thin films for solid-state batteries, a promising approach in the quest for safer batteries with higher energy densities at lower fabrication costs. In this study, we use a scalable cosputtering process to fabricate LLZO thin films with subsequent postannealing at a temperature of 700 °C, significantly below the sintering temperatures employed in ceramic pellet processing. We investigate the roles that Li excess and incorporation of Al play in the film’s crystalline phase, microstructure, phase stability, and, ultimately, ionic conductivity. Our results reveal that improving the conductivity of LLZO thin films requires not only the stabilization of the cubic phase but especially the densification of the film and the minimization of the proton exchange degradation mechanism in the presence of moisture an...

In this work, we realized a flexible electrolyte-gated field-effect transistor (EG-FET) based on a spray-coated semi-conducting single-walled carbon nanotube (SWCNTs) network. The device was functionalized with anti-spermidine antibodies for a specific detection of polyamine spermidine - a well-known chemical indicator of food quality. The spray-coated SWCNTs films were modified with a bifunctional molecule, which binds to the nanotubes via non-covalent π−π interactions and leaves a free NHS-ester group for amide coupling of the antibodies, ensuring controlled immobilization. Transfer and output curves were recorded for device characterization, showing a typical p-type behavior with an on–off ratio of 190 A/A and a threshold voltage around 0 V. The calibration curve of the fabricated EG-FET immunosensor shows a linear detection range for spermidine from 0.001 to 100 nM, with 99.83% coefficient of determination.

In this work, we present a novel flexible amperometric sensor for nitrate detection, based on a silver (Ag) working electrode modified with single-walled carbon nanotubes (SWCNTs) and copper (Cu). A simple and low-cost fabrication technique combining printing and electrochemical deposition was used: after spray deposition of SWCNTs on the screen-printed Ag working electrode, Cu was electrodeposited. The electrochemical performance of our sensors was analyzed and compared to reference sensors fabricated without SWCNTs (Cu/Ag), proving the capability of SWCNTs to improve the sensitivity and the performance of the sensors thanks to the increased electroactive surface area. In fact, the Cu/SWCNTs/Ag sensors showed higher catalytic activity towards the electro-reduction of nitrate (sensitivity: 18.19 µA/mM), as well as a lower limit of detection (LOD: 0.281 nM) in comparison to the Cu/Ag sensors (sensitivity: 12.19 µA/mM and LOD: 0.381 nM). Full sensor functionality after repetitive mechanical bending to 5 mm radius was also proven.

Structural defects such as voids and compositional inhomogeneities may affect the performance of Cu(In,Ga)Se2 (CIGS) solar cells. We analyzed the morphology and elemental distributions in co-evaporated CIGS thin films at the different stages of the CIGS growth by energy-dispersive x-ray spectroscopy in a transmission electron microscope. Accumulation of Cu-Se phases was found at crevices and at grain boundaries after the Cu-rich intermediate stage of the CIGS deposition sequence. It was found, that voids are caused by Cu out-diffusion from crevices and GBs during the final deposition stage. The Cu inhomogeneities lead to non-uniform diffusivities of In and Ga, resulting in lateral inhomogeneities of the In and Ga distribution. Two and three-dimensional simulations were used to investigate the impact of the inhomogeneities and voids on the solar cell performance. A significant impact of voids was found, indicating that the unpassivated voids reduce the open-circuit voltage and fill factor due to the introduction of free surfaces with high recombination velocities close to the CIGS/CdS junction. We thus suggest that voids, and possibly inhomogeneities, limit the efficiency of solar cells based on three-stage co-evaporated CIGS thin films. Passivation of the voids’ internal surface may reduce their detrimental effects., Graphical Abstract

In this work, we demonstrate the advantages and the potentials of dispense printing (V-One, Voltera) for the realization of conductive contacts of flexible electronics. Printing parameters were optimized for Ag inks on different substrates (PCB, Si/SiO 2 and polyimide), leading to straight homogeneous printed lines with minimum feature size of $159\pm 22\mu \mathrm{m}$ . Hybrid-manufactured Ag/InGaZnO Schottky diodes, with an average rectification ratio of 80 and an ON voltage of 0.63 V, were successfully demonstrated on flexible foils.

The underlying beneficial mechanism of heavy alkali postdeposition treatment (PDT) of Cu(In,Ga)Se

Within the analysis of solar cells with multi-modal X-ray microscopy, X-ray fluorescence (XRF) measurements have become a reliable source for evaluating elemental distributions. While XRF measurements can unveil the elemental distribution at unparalleled sensitivity and spatial resolution, the quantitative analysis is challenged by effects such as self-absorption and further complicated by the inclusion of multiple detector modules. Here, we showcase the exemplary analysis of XRF spectra obtained from a Cu(In, Ga)Se2 solar cell utilizing four detector modules. After cataloging typical features found in XRF spectra, we demonstrate the inclusion of detector modules with individual absorption correction. This results in quantitative stoichiometric ratios of the critical absorber elements Cu, In, and Ga that are in good agreement with the nominal ratios. These results are particularly relevant in view of future measurements at diffraction-limited synchrotron beamlines: in order to profit from the boost of nano-focused photon flux, XRF measurements will require multiple detector modules, for which we demonstrate an approach of quantitative analysis.

Heterocyclic amine histamine is a well-known foodborne toxicant (mostly linked to &ldquo, scombroid poisoning&rdquo, ) synthesized from the microbial decarboxylation of amino acid histidine. In this work, we report the fabrication of a flexible screen-printed immunosensor based on a silver electrode coated with single-walled carbon nanotubes (SWCNTs) for the detection of histamine directly in fish samples. Biosensors were realized by first spray depositing SWCNTs on the working electrodes and by subsequently treating them with oxygen plasma to reduce the unwanted effects related to their hydrophobicity. Next, anti-histamine antibodies were directly immobilized on the treated SWCNTs. Histamine was detected using the typical reaction of histamine and histamine-labeled with horseradish peroxidase (HRP) competing to bind with anti-histamine antibodies. The developed immunosensor shows a wide linear detection range from 0.005 to 50 ng/mL for histamine samples, with a coefficient of determination as high as 98.05%. Average recoveries in fish samples were observed from 96.00% to 104.7%. The biosensor also shows good selectivity (less than 3% relative response for cadaverine, putrescine, and tyramine), reproducibility, mechanical and time stability, being a promising analytical tool for the analysis of histamine, as well as of other food hazards.

Chalcopyrite solar cells achieve efficiencies above 23%. The latest improvements are due to post-deposition treatments (PDT) with heavy alkalis. This study provides a comprehensive description of the effect of PDT on the chemical and electronic structure of surface and bulk of Cu(In,Ga)Se-2. Chemical changes at the surface appear similar, independent of absorber or alkali. However, the effect on the surface electronic structure differs with absorber or type of treatment, although the improvement of the solar cell efficiency is the same. Thus, changes at the surface cannot be the only effect of the PDT treatment. The main effect of PDT with heavy alkalis concerns bulk recombination. The reduction in bulk recombination goes along with a reduced density of electronic tail states. Improvements in open-circuit voltage appear together with reduced band bending at grain boundaries. Heavy alkalis accumulate at grain boundaries and are not detected in the grains. This behavior is understood by the energetics of the formation of single-phase Cu-alkali compounds. Thus, the efficiency improvement with heavy alkali PDT can be attributed to reduced band bending at grain boundaries, which reduces tail states and nonradiative recombination and is caused by accumulation of heavy alkalis at grain boundaries. This work was supported by the European Union's Horizon 2020 research and innovation program under grant agreement no. 641004 (Sharc25) and by the Swiss State Secretariat for Education, Research and Innovation (SERI) under contract number 15.0158. Siebentritt, S (reprint author), Univ Luxembourg, Lab Photovolta, Phys & Mat Sci Res Unit, 41 Rue Brill, L-4422 Belvaux, Luxembourg. susanne.siebentritt@uni.lu

Cu In,Ga Se2 CIGSe is a promising absorber material for thin film photovoltaic devices. A key procedure to achieve high efficiencies is the application of alkali fluoride postdeposition treatments PDT of the CIGSe surface. While the effects of the PDT on the directly impacted CIGSe front surface have been subject to extensive studies, less is known about the impact on the deeply buried CIGSe Mo interface. Exposing the CIGSe absorber backside by stripping it off the Mo back contact allows to use surface sensitive photoelectron spectroscopy to study the chemical and electronic structure of this interface in unprecedented detail. CIGSe Mo stacks prepared using NaF only and combined NaF RbF with optimal and excess amount of RbF PDT are studied. Rb is detected accumulating at the backside of the RbF treated CIGSe absorbers in conjunction with a depletion of Na. The exposed CIGSe backsides display a Cu deficient surface region, with increased presence of Rb correlating with a decreased Cu content. Rb appears to be incorporated into the Cu deficient absorber region as previously detected on the front surface. However, in contrast to the front surface, no distinct, secondary Rb amp; 63743;In amp; 63743;Se type phase is found at the back surface

In-situ Se flux control system is applied for the growth of Cu(In,Ga)Se 2 (CIGS) absorber layers by a multi stage thermal co-deposition of elements at low substrate temperature below 500 °C. It was revealed that the composition depth profile of the [Ga]/([In]+[Ga]) (GGI) ratio is affected by the [Se]/[Metal] flux ratio. It was observed for the solar cell properties that the change in the depth profiles of GGI induced by the change of [Se]/[Metal] resulted in an increase in the J SC and a decrease in the FF, and hence little influence on the efficiency. Under control of [Se]/[Metal] ratio during the deposition process, the effect of CIGS layer thickness on the solar cell properties was investigated. With increase in the thickness up to 2.8 μm, the short circuit current density was increased to over 35 mA/cm 2 w/o AR coating, resulting in conversion efficiency above 18% using low temperature deposition method.

Highly efficient thin film solar cells based on co-evaporated Cu(In,Ga)Se2 (CIGS) absorbers are typically grown with a [Ga]/([Ga] + [In]) (GGI) gradient across the thickness and a Cu-poor composition. Upon increasing the Cu content towards the CIGS stoichiometry, lower defect density is expected, which should lead to increased absorption in the near-infrared (NIR), diffusion length and carrier collection. Further, optimization of the GGI grading is expected to increase the NIR response. In this contribution [Cu]/([In] + [Ga]) (CGI) values are increased by shortening the deposition stage after the first stoichiometric point. In order to obtain comparable Ga contents at the interface for proper band alignment, the front GGI gradings were actively modified. With a relative CGI increase of 7%, we observe an increased photocurrent, originating from an improved NIR external quantum efficiency response. By characterizing the modified absorber properties by reflection-transmission spectroscopy, we attribute the observed behavior to changes in the optical properties rather than to improved carrier collection. Cu-dependent modifications of the NIR-absorption coefficients are likely to be responsible for the variations in the optical properties, which is supported by device simulations. Adequate re-adjustments of the co-evaporation process and of the alkali-fluorides post-deposition treatments allow maintaining Voc and FF values, yielding an overall increase of efficiency as compared to a reference baseline. © 2016 The Authors. Progress in Photovoltaics: Research and Applications published by John Wiley & Sons Ltd.

Multi-junction solar cells are known to have a considerably increased efficiency potential over their typical single junction counterparts. In order to produce low cost and lightweight multi-junction devices, the availability of suitable narrow ( In this contribution we report on the RbF post deposition treatment of narrow bandgap CIGS absorbers grown with a single bandgap grading approach. We discuss the necessary deposition conditions and the observed improvements on solar cells performance. A certified record efficiency of 18.0% for an absorber with 1.00 eV optoelectronic bandgap is presented and its suitability for perovskite/CIGS tandem devices is shown.

This review summarizes the current status of Cu(In,Ga)(S,Se)2 (CIGS) thin film solar cell technology with a focus on recent advancements and emerging concepts intended for higher efficiency and novel applications. The recent developments and trends of research in laboratories and industrial achievements communicated within the last years are reviewed, and the major developments linked to alkali post deposition treatment and composition grading in CIGS, surface passivation, buffer, and transparent contact layers are emphasized. Encouraging results have been achieved for CIGS-based tandem solar cells and for improvement in low light device performance. Challenges of technology transfer of lab's record high efficiency cells to average industrial production are obvious from the reported efficiency values. One section is dedicated to development and opportunities offered by flexible and lightweight CIGS modules. Copyright © 2016 John Wiley & Sons, Ltd.

The electrical properties of polycrystalline ZnO thin films with grain boundary limited charge transport depend significantly on the degree of chemisorbed adsorbate (CxOyHz) coverage at grain boundaries and on the surface. Here we report the evolution of carbon adsorbates in chemical bath deposited (CBD) aluminum doped ZnO (AZO) thin films during post-deposition UV light exposure and degradation in humid atmosphere. As CBD AZO intrinsically contains carbon impurities stemming from the addition of citrate during the deposition, sputtered AZO is examined in parallel as a nominally carbon-free reference. UV illumination decomposes citrate impurities in CBD AZO, but the residual carbon compounds are not effectively removed from the bulk part of the layer. At the same time, charge-trapping oxygen species at grain boundaries are desorbed, increasing the carrier density and mobility. Exposure to humid atmosphere decreases the electrical conductivity of CBD AZO, which is caused by the chemisorption of environmental oxygen species and the formation of zinc carbonate.

The influence of sodium and rubidium postdeposition treatment on the quality of Cu(In,Ga)Se2 thin-film absorbers is investigated. The quasi-Fermi level splitting (QFLS), measured via photoluminescence (PL), is used as the metric of quality of the absorber. To evaluate the QFLS values in the graded absorber of state-of-the-art devices, it is necessary to know at which location the luminescence is generated. Here we show, by measuring the PL in different geometries, that the photons originate from the global band gap minimum inside the bulk. We use this knowledge to compare the QFLS in different absorbers, where our results show that the QFLS is higher in absorbers that were treated with NaF + RbF than in absorbers that were only treated with NaF or not treated at all. We attribute this increase to a reduced nonradiative recombination, even before cadmium sulfide deposition. A decreased difference between QFLS and open-circuit voltage in the corresponding finished solar cells also reveals an improved CdS/CIGS interface. Both effects ultimately lead to a higher efficiency.

The introduction of a KF postdeposition treatment (KF PDT) of Cu(InGa)Se2 (CIGS) thin films has led to the achievement of several consecutive new world record efficiencies up to 21.7 for the CIGS solar cell technology. The beneficial effect of the KF PDT on the photovoltaic parameters was observed by several groups in spite of differing growth methods of the CIGS layer. For CIGS evaporated at lower temperature on alkali free flexible plastic substrates a postdeposition treatment to add Na was already successfully applied. However with the introduction of additional KF under comparable conditions distinctly different influences on the final absorber alkali content as well as surface properties are observed. In this work we discuss in more detail the intrinsically different role of both alkali treatments by combining several microstructural and compositional analysis methods. The ion exchange of Na by K in the bulk of the absorber is carefully analyzed and further evidence for the formation of a K containing layer on the CIGS surface with increased surface reactivity is given. These results shall serve as a basis for the further understanding of the effects of alkali PDT on CIGS and help identify research needs to achieve even higher efficiencies. (Figure Presented). © 2015 American Chemical Society.

Cu(In,Ga)Se2 based solar cells have reached efficiencies close to 23%. Further knowledge-driven improvements require accurate determination of the material properties. Here, we present refractive indices for all layers in Cu(In,Ga)Se2 solar cells with high efficiency. The optical bandgap of Cu(In,Ga)Se2 does not depend on the Cu content in the explored composition range, while the absorption coefficient value is primarily determined by the Cu content. An expression for the absorption spectrum is proposed, with Ga and Cu compositions as parameters. This set of parameters allows accurate device simulations to understand remaining absorption and carrier collection losses and develop strategies to improve performances.

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This work investigates the effect of Cu content and Ga grading on the performance of CIGS cells, by means of numerical simulations and comparison with corresponding experiments. Different Ga profiles and Cu average concentrations are considered. We show that the optical effect of Cu content must be properly taken into account to model NIR absorption. As far as the GGI profile is concerned, we show that the main improvement can be obtained by increasing the GGI ratio toward the back-side; an optimized notch bandgap profile can be designed with the help of these indications.

Quantum efficiency measurements of state of the art Cu(In,Ga)Se2 (CIGS) thin film solar cells reveal current losses in the near infrared spectral region. These losses can be ascribed to inadequate optical absorption or poor collection of photogenerated charge carriers. Insight on the limiting mechanism is crucial for the development of more efficient devices. The electron beam induced current measurement technique applied on device cross-sections promises an experimental access to depth resolved information about the charge carrier collection probability. Here, this technique is used to show that charge carrier collection in CIGS deposited by multistage co-evaporation at low temperature is efficient over the optically active region and collection losses are minor as compared to the optical ones. Implications on the favorable absorber design are discussed. Furthermore, it is observed that the measurement is strongly affected by cross-section surface recombination and an accurate determination of the collection efficiency is not possible. Therefore it is proposed and shown that the use of an Al2 O3 layer deposited onto the cleaved cross-section significantly improves the accuracy of the measurement by reducing the surface recombination. A model for the passivation mechanism is presented and the passivation concept is extended to other solar cell technologies such as CdTe and Cu2 (Zn,Sn)(S,Se)4 .

In this work we use numerical simulations to study how the doping profile extracted by the commonly used C-V technique is influenced by the solar cell main features, as the doping and thickness of different layers, or the conduction band offsets at hero-interfaces. The doping profiles dependence on temperature is also investigated. The effect of both acceptor and donor deep defects of different energy and density on the simulated doping profile has been analyzed and correlated with experimental results, in order to give indications for the correct interpretation of measured doping profile.

Semi-transparent perovskite solar cells are highly attractive for a wide range of applications, such as bifacial and tandem solar cells; however, the power conversion efficiency of semi-transparent devices still lags behind due to missing suitable transparent rear electrode or deposition process. Here we report a low-temperature process for efficient semi-transparent planar perovskite solar cells. A hybrid thermal evaporation–spin coating technique is developed to allow the introduction of PCBM in regular device configuration, which facilitates the growth of high-quality absorber, resulting in hysteresis-free devices. We employ high-mobility hydrogenated indium oxide as transparent rear electrode by room-temperature radio-frequency magnetron sputtering, yielding a semi-transparent solar cell with steady-state efficiency of 14.2% along with 72% average transmittance in the near-infrared region. With such semi-transparent devices, we show a substantial power enhancement when operating as bifacial solar cell, and in combination with low-bandgap copper indium gallium diselenide we further demonstrate 20.5% efficiency in four-terminal tandem configuration., Perovskite solar cells already exhibit large efficiencies above 20%. Here, the authors use a low temperature sputtering process to fabricate semi-transparent perovskite solar cells, demonstrating bifacial operation and a 4-terminal tandem with CIGS solar cells surpassing single junction cells.

A promising way to enhance the efficiency of CIGS solar cells is by combining them with perovskite solar cells in tandem devices. However, so far, such tandem devices had limited efficiency due to challenges in developing NIR-transparent perovskite top cells, which allow photons with energy below the perovskite band gap to be transmitted to the bottom cell. Here, a process for the fabrication of NIR-transparent perovskite solar cells is presented, which enables power conversion efficiencies up to 12.1% combined with an average sub-band gap transmission of 71% for photons with wavelength between 800 and 1000 nm. The combination of a NIR-transparent perovskite top cell with a CIGS bottom cell enabled a tandem device with 19.5% efficiency, which is the highest reported efficiency for a polycrystalline thin film tandem solar cell. Future developments of perovskite/CIGS tandem devices are discussed and prospects for devices with efficiency toward and above 27% are given.

The underlying beneficial mechanism of heavy alkali postdeposition treatment (PDT) of Cu(In,Ga)Se2 thin-film solar cell absorbers that led to new record efficiencies in recent years is studied using photoelectron spectroscopy. Excitation energies between 40.8 eV and 6 keV were used to examine the near-surface region of Cu(In,Ga)Se2 thin-film solar cell absorbers that underwent NaF and combined NaF/RbF PDT. The already Cu-deficient surface region after NaF PDT, which is modeled as a Cu:(In + Ga):Se = 1:5:8 phase, shows further depletion after NaF/RbF PDT and seems to incorporate some Rb. Additionally, we have found strong indications for the NaF/RbF PDT-induced formation of a Rb-In-Se-type compound with a 1:1:2 stoichiometry partially covering the absorber surface. The electronic Cu(In,Ga)Se2 structure is modified due to the RbF treatment, with a pronounced shift in the valence band maximum away from the Fermi level in the immediate vicinity of the surface.

Postdeposition treatments (PDTs) with sodium fluoride (NaF) and potassium fluoride (KF) were introduced as a way to improve the efficiency of Cu(In,Ga)Se2 (CIGS) based solar cells. Here, we apply postdeposition treatments with rubidium fluoride (RbF) to low-temperature coevaporated CIGS absorbers after a first PDT with NaF and compare the effects of the addition of Rb and K on the solar cell performance and material properties of the CIGS films. KF and RbF PDTs lead to similar improvements in the open-circuit voltage (Voc) and fill factor (FF), while allowing a reduction of the thickness of the cadmium sulfide (CdS) buffer layer without loss in electronic performance. KF and RbF PDTs lead to comparable modifications of the morphology and composition of the CIGS films. After the PDT, K and Rb accumulate in a nanopatterned copper-poor secondary phase at the CIGS surface, while also diffusing within the CIGS layer and strongly reducing the concentration of lighter alkali element sodium. These findings corrob...

Knowledge of the absorber bandgap is often needed for assessing the junction quality of a thin film solar cell, for example when computing the open-circuit voltage deficit. The bandgap is typically estimated from the routine measurement of the external quantum efficiency (EQE) of finished devices. However the extraction becomes ambiguous in the case of very thin absorbers, or in presence of bandgap gradients or collection issues of charge carriers. This work reviews several methods for the determination of the bandgap from EQE measurements and discusses their validity conditions. The numerical results are compared based on experimental EQE of several different thin film solar cells such as CuInGaSe2, CuInSe2, CdTe, CuZnSnSe and perovskite, and systematic trends are identified. Numerical simulations are also performed to illustrate the behavior of the different bandgap extraction methods in presence of a bandgap gradient and different magnitudes of the exponential tail states.

Time-resolved photoluminescence (TRPL) is applied to determine an effective lifetime of minority charge carriers in semiconductors. Such effective lifetimes include recombination channels in the bulk as well as at the surfaces and interfaces of the device. In the case of Cu(In,Ga)Se2 absorbers used for solar cell applications, trapping of minority carriers has also been reported to impact the effective minority carrier lifetime. Trapping can be indicated by an increased temperature dependence of the experimentally determined photoluminescence decay time when compared to the temperature dependence of Shockley–Read–Hall (SRH) recombination alone and can lead to an overestimation of the minority carrier lifetime. Here, it is shown by technology computer-aided design (TCAD) simulations and by experiment that the intentional double-graded bandgap profile of high efficiency Cu(In,Ga)Se2 absorbers causes a temperature dependence of the PL decay time similar to trapping in case of a recombinative front surface. It is demonstrated that a passivated front surface results in a temperature dependence of the decay time that can be explained without minority carrier trapping and thus enables the assessment of the absorber quality by means of the minority carrier lifetime. Comparison with the absolute PL yield and the quasi-Fermi-level splitting (QFLS) corroborate the conclusion that the measured decay time corresponds to the bulk minority carrier lifetime of 250 ns for the double-graded CIGS absorber under investigation., Graphical Abstract

In this work, we realized a printed immunosensor based on a competitive enzyme-linked immunosorbent assay (ELISA) to allow histamine detection. We investigated the effect of modifying the immunosensor electrodes with spray-deposited poly(3,4-ethyldioxythiophene)poly(styrenesulfunate) (PEDOT:PSS) and single walled carbon nanotube (SWCNT) films. Cyclic voltammetry (CV) was used to characterize the sensor performance in terms of electron transfer kinetics and to prove an enhancement of the electrode active surface area up to 29.1%, due to the use of the additional PEDOT:PSS/SWCNT film. The calibration curve of the so-realized immunosensor (obtained by chronoamperometry measurements) shows a linear detection range of histamine from 0.05 to 50 ng/ml, with 95.03% coefficient of determination.