Enhanced Self Assembled Monolayer Surface Coverage by ALD NiO in p i n Perovskite Solar Cells

Metal halide perovskites have attracted tremendous attention due to their excellent electronic properties. Recent advancements in device performance and stability of perovskite solar cells PSCs have been achieved with the application of self assembled monolayers SAMs , serving as stand alone hole transport layers in the p i n architecture. Specifically, phosphonic acid SAMs, directly functionalizing indium tin oxide ITO , are presently adopted for highly efficient devices. Despite their successes, so far, little is known about the surface coverage of SAMs on ITO used in PSCs application, which can affect the device performance, as non covered areas can result in shunting or low open circuit voltage. In this study, we investigate the surface coverage of SAMs on ITO and observe that the SAM of MeO 2PACz [2 3,6 dimethoxy 9H carbazol 9 yl ethyl]phosphonic acid inhomogeneously covers the ITO substrate. Instead, when adopting an intermediate layer of NiO between ITO and the SAM, the homogeneity, and hence the surface coverage of the SAM, improve. In this work, NiO is processed by plasma assisted atomic layer deposition ALD with Ni MeCp 2 as the precursor and O2 plasma as the co reactant. Specifically, the presence of ALD NiO leads to a homogeneous distribution of SAM molecules on the metal oxide area, accompanied by a high shunt resistance in the devices with respect to those with SAM directly processed on ITO. At the same time, the SAM is key to the improvement of the open circuit voltage of NiO MeO 2PACz devices compared to those with NiO alone. Thus, the combination of NiO and SAM results in a narrower distribution of device performance reaching a more than 20 efficient champion device. The enhancement of SAM coverage in the presence of NiO is corroborated by several characterization techniques including advanced imaging by transmission electron microscopy TEM , elemental composition quantification by Rutherford backscattering spectrometry RBS , and conductive atomic force microscopy c AFM mapping. We believe this finding will further promote the usage of phosphonic acid based SAM molecules in perovskite P

Deconvolution analysis for classifying gastric adenocarcinoma patients based on differential scanning calorimetry serum thermograms

Recently, differential scanning calorimetry (DSC) has been acknowledged as a novel tool for diagnosing and monitoring several diseases. This highly sensitive technique has been traditionally used to study thermally induced protein folding/unfolding transitions. In previous research papers, DSC profiles from blood samples of patients were analyzed and they exhibited marked differences in the thermal denaturation profile. Thus, we investigated the use of this novel technology in blood serum samples from 25 healthy subjects and 30 patients with gastric adenocarcinoma (GAC) at different stages of tumor development with a new multiparametric approach. The analysis of the calorimetric profiles of blood serum from GAC patients allowed us to discriminate three stages of cancer development (I to III) from those of healthy individuals. After a multiparametric analysis, a classification of blood serum DSC parameters from patients with GAC is proposed. Certain parameters exhibited significant differences (P < 0.05) and allowed the discrimination of healthy subjects/patients from patients at different tumor stages. The results of this work validate DSC as a novel technique for GAC patient classification and staging, and offer new graphical tools and value ranges for the acquired parameters in order to discriminate healthy from diseased subjects with increased disease burden.Peer Reviewe

The interaction between hybrid organic-inorganic halide perovskite and selective contacts in perovskite solar cells: An infrared spectroscopy study

The interaction of hybrid organic-inorganic halide perovskite and selective contacts is crucial to get efficient, stable and hysteresis-free perovskite-based solar cells. In this report, we analyze the vibrational properties of methylammonium lead halide perovskites deposited on different substrates by infrared absorption (IR) measurements (4000-500 cm). The materials employed as substrates are not only characterized by different chemical natures (TiO, ZnO and AlO), but also by different morphologies. For all of them, we have investigated the influence of these substrate properties on perovskite formation and its degradation by humidity. The effect of selective-hole contact (Spiro-OmeTad and P3HT) layers on the degradation rate by moisture has also been studied. Our IR results reveal the existence of a strong interaction between perovskite and all ZnO materials considered, evidenced by a shift of the peaks related to the N-H vibrational modes. The interaction even induces a morphological change in ZnO nanoparticles after perovskite deposition, pointing to an acid-base reaction that takes place through the NH groups of the methylammonium cation. Our IR and X-ray diffraction results also indicate that this specific interaction favors perovskite decomposition and PbI formation for ZnO/perovskite films subjected to humid conditions. Although no interaction is observed for TiO, AlO, and the hole selective contact, the morphology and chemical nature of both contacts appear to play an important role in the rate of degradation upon exposure to moisture.We thank the Regional Government of Andalusia for financial support via grants FQM1851 and FQM2310 and Ministerio de Economia y Competitividad under grants MAT2013-47192-C3-3-R and MAT2013-42900-P. MINECO/ICTI2013-2016/MAT2013-42900-

Organic dyes for the sensitization of nanostructured ZnO photoanodes: effect of the anchoring functions

International audienceAmong all n-type metal oxide semiconductors that can be used in solar cells as photoanode, ZnO is one of the most appealing aEternatives to the ubiquitous TiO2. This material offers some potentially favourable characteristics with respect to TiO2, such as higher eEectron mobility in the bulk and a rich variety of nanostructures. However, ZnO has certain drawbacks as photoanode material for example, a poor chemical stability and a slower charge separation process at the ZnO interface that reduces the eEectron injection rate. Therefore, in the case of dye-sensitized solar cells, the search of new dyes with a higher Eight harvesting efficiency and specifically designed to bind to ZnO can be considered as a possible strategy to improve performance in systems characterized by a Low eEectron injection rate. In this work the optical eEectrochemical and photovoltaic properties of a family of purely organic sensitizers with various anchoring groups have been investigated and compared with the most commonly used ruthenium dye N719. In particuar, we have shown that the structurally simple organic dye coded RK1 is an excellent sensitizer for ZnO photoanodes. Thanks to this molecule, the energy conversion efficiency under standard conditions (1 sun AM 1.5 illumination) empEoying ZnO-based photoanodes reached 3.7%, which is more than two times higher than obtained with the N719 dye studied under the same conditions

Towards a universal approach for the analysis of impedance spectra of perovskite solar cells equivalent circuits and empirical analysis

Impedance spectroscopy is a powerful electrochemical small-perturbation technique that provides dynamic electrical data in solar cells. This technique has been widely used to characterize dye-sensitized solar cells and perovskite solar cells (PSCs). Physical parameters are normally obtained by fitting to an equivalent circuit, composed of electrical elements which theoretically correspond to physical processes involved in the photoconversion process. A variety of equivalent circuits to model the impedance spectra of PSCs are commonly used by different research groups. In this work, we evaluate their performance and adequacy. We demonstrate the analytical and numerical equivalence of impedance expressions for Voight, matryoshka, and hybrid circuits, which are used to fit a typical impedance spectrum of a PSC and compare the resulting parameters to the empirical values obtained without any equivalent circuit. The numerical equivalence can be demonstrated by using two- and three-component impedance spectra. In contrast, Maxwell-type equivalent circuits reveal parameters that have a more complex relation to empirical values. The presence of inductive effects such as “loops” and “negative tails” in impedance spectra are also discussed in terms of negative values of resistances and capacitances. We propose a general protocol to analyze impedance data of PSCs and to extract useful information from them

Universal Features of Electron Dynamics in Solar Cells with TiO₂ Contact: From Dye Solar Cells to Perovskite Solar Cells

The electron dynamics of solar cells with mesoporous TiO₂ contact is studied by electrochemical small-perturbation techniques. The study involved dye solar cells (DSC), solid-state perovskite solar cells (SSPSC), and devices where the perovskite acts as sensitizer in a liquid-junction device. Using a transport-recombination continuity equation we found that mid-frequency time constants are proper lifetimes that determine the current–voltage curve. This is not the case for the SSPSC, where a lifetime of ∼1 μs, 1 order of magnitude longer, is required to reproduce the current–voltage curve. This mismatch is attributed to the dielectric response on the mid-frequency component. Correcting for this effect, lifetimes lie on a common exponential trend with respect to open-circuit voltage. Electron transport times share a common trend line too. This universal behavior of lifetimes and transport times suggests that the main difference between the cells is the power to populate the mesoporous TiO₂ contact with electrons

Universal Features of Electron Dynamics in Solar Cells with TiO₂ Contact: From Dye Solar Cells to Perovskite Solar Cells

The electron dynamics of solar cells with mesoporous TiO₂ contact is studied by electrochemical small-perturbation techniques. The study involved dye solar cells (DSC), solid-state perovskite solar cells (SSPSC), and devices where the perovskite acts as sensitizer in a liquid-junction device. Using a transport-recombination continuity equation we found that mid-frequency time constants are proper lifetimes that determine the current–voltage curve. This is not the case for the SSPSC, where a lifetime of ∼1 μs, 1 order of magnitude longer, is required to reproduce the current–voltage curve. This mismatch is attributed to the dielectric response on the mid-frequency component. Correcting for this effect, lifetimes lie on a common exponential trend with respect to open-circuit voltage. Electron transport times share a common trend line too. This universal behavior of lifetimes and transport times suggests that the main difference between the cells is the power to populate the mesoporous TiO₂ contact with electrons

Insights into the morphological pattern of erythrocytes' aging: coupling quantitative AFM data to microcalorimetry and Raman spectroscopy

Erythrocytes (RBCs) constitute a very interesting class of cells both for their physiological function and for a variety of peculiarities. Due to their exceptionally strong relationship with the environment, the morphology and nanoscale characteristics of these cells can reveal their biochemical status and structural integrity. Among the possible subjects of investigations, the RBCs' ageing is of the utmost importance. This is a fundamental phenomenon that, in physiological conditions, triggers the cell turnover and ensures the blood homeostasis. With these premises, in recent years, we have presented an atomic force microscopy–based methodology to characterize the patterns of RBC ageing from the morphological point of view. In the present work, we used an ageing protocol more similar to the physiological conditions and we used differential scanning calorimetry and atomic force microscopy to probe the cross correlation between important structural and functional proteins. We also assessed the role played by fundamental structural and membrane proteins in the development of the most relevant morphological intermediates observed along the ageing. Furthermore, we coupled the morphological ageing patterns to the (bio)chemical alterations detected by Raman spectroscopy. This allowed identifying the chronology of the ageing morphologies and the metabolic pathways most involved in their development. As a whole, the present study provides the base to correlate specific molecular alterations to the development of structural anomalies, and these latter to the functional status of blood cells

Impact of moisture on efficiency-determining electronic processes in perovskite solar cells

Moisture-induced degradation in perovskite solar cells was thoroughly investigated by structural (SEM, EDS, XRD and XPS) and device characterization (impedance and intensity modulated photocurrent spectroscopy) techniques. Both the influence of the perovskite composition and the nature of the hole selective material were analyzed. The degradation rate was found to be significantly slower for mixed perovskites and P3HT-based devices. However, for a fixed degradation degree (defined as a 50% drop from the initial photocurrent), all configurations show similar features in small-perturbation analysis. Thus, a new mid-frequency signal appears in the impedance response, which seems to be related to charge accumulation at the interfaces. In addition, faster recombination, with a more important surface contribution, and slower transport were clearly inferred from our results. Both features can be associated with the deterioration of the contacts and the formation of a higher number of grain boundaries