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In the scenario of the new emerging photovoltaics, kesterites play a lead role in the thin-film solar cell technologies. This class of compounds, mainly represented by the pure-sulfide form Cu2ZnSnS4 (CZTS) and the sulfo-selenide form Cu2ZnSn(S,Se)4 (CZTSSe), shows unique characteristics and stands as a promising p-type absorber material thanks to its high absorption coefficient, high cost-effectiveness and low toxicity. However, CdS is commonly used as the n-type partner (buffer layer) in kesterite solar cells but, beyond its toxicity, it has a nonoptimal band alignment with kesterites and exhibits parasitic absorption at low wavelengths due to its bandgap. Several efforts have been made in the last decade, to replace CdS with a suitable, Cd-free, both environmentally and economically sustainable buffer layer, and many times with successful results allowing not only to equal, but also to overcome in few cases the performances of the corresponding CdS-based reference devices. Zn1-xSnxO for instance leads to higher efficiencies than CdS when coupled with pure-sulfide CZTS, while Zn(O,S) seems to couple better with CZTSSe. TiO2 has been also considered as suitable buffer layer for kesterites and, in the last few years, several works have been reported both theoretical and experimental, showing very promising results. In this review we summarize the efforts and the improvements recorded by the scientific community working on this topic in the last ten years, with the aim to supply a landmark useful to design future experiments in a more efficient way and to push forward the related research activities, in order to fully overcome CdS limitations and to promote thin-film kesterite devices to higher performances.

Pure sulfide kesterite (Cu2ZnSnS4) is one of the most promising emerging photovoltaic technologies thanks to its excellent absorption coefficient, cost-effectiveness, and environmental sustainability. However, record efficiencies are not exceeding 11% due to several issues, such as absorber defects or a nonoptimal band alignment with the toxic but conventionally used CdS buffer layer. To get rid of it, several efforts have been made in the past few years. Among recent theoretical works, TiO2 has been suggested as a suitable buffer layer due to its optical and electrical properties, giving extremely promising results in device simulation. However, there are few experimental examples combining TiO2 with kesterite, and they generally show very modest performances. In this Letter, we report on the preliminary and promising results of our experimental procedure for the production of Cd-free kesterite photovoltaic devices featuring ALD-TiO2 as a buffer layer, leading to efficiencies comparable with our CZTS/CdS reference devices.

This work presents the design and experimental validation of a low-noise amplifier based on a ultra-low-noise JFET for noise characterization of materials samples for neural interfaces. The JFET LNA amplifies the sample noise power by 46 dB well above a lock-in amplifier noise floor, used as spectrum analyzer for noise characterization. The LNA exploits the high gm and low flicker corner frequency of JFETs to achieve 0.15 dB noise figure. The JFET LNA has been characterized in terms of frequency response and noise power spectrum and experimentally validated by characterizing the noise spectrum of a platinum silicide (PtSi) sample.

In vitro and in vivo stimulation and recording of neuron action potential is currently achieved with microelectrode arrays, either in planar or 3D geometries, adopting different materials and strategies. IrO2 is a conductive oxide known for its excellent biocompatibility, good adhesion on different substrates, and charge injection capabilities higher than noble metals. Atomic layer deposition (ALD) allows excellent conformal growth, which can be exploited on 3D nanoelectrode arrays. In this work, we disclose the growth of nanocrystalline rutile IrO2 at T = 150 °C adopting a new plasma-assisted ALD (PA-ALD) process. The morphological, structural, physical, chemical, and electrochemical properties of the IrO2 thin films are reported. To the best of our knowledge, the electrochemical characterization of the electrode/electrolyte interface in terms of charge injection capacity, charge storage capacity, and double-layer capacitance for IrO2 grown by PA-ALD was not reported yet. IrO2 grown on PtSi reveals a double-layer capacitance (Cdl) above 300 µF∙cm−2, and a charge injection capacity of 0.22 ± 0.01 mC∙cm−2 for an electrode of 1.0 cm2, confirming IrO2 grown by PA-ALD as an excellent material for neuroelectronic applications.

Cu2ZnSnS4 (CZTS) is a promising absorber material to produce thin film solar cells thanks to its high absorption coefficient, low cost and low toxicity. CdS is commonly used as a buffer layer for CZTS solar cells but, beyond its toxicity, it has a nonoptimal band alignment with CZTS. ZnxSn1−xO (ZTO), based on earth-abundant and nontoxic elements and with a large and tunable band gap, is a suitable alternative buffer layer. In this paper, the atomic layer deposition (ALD) of ZTO was employed by testing different compositions and thicknesses. ALD not only leads to very compact and homogenous ZTO layers (enabling tuning the stoichiometry of the ZTO so prepared) but also makes the i-ZnO layer (usually sandwiched between the buffer layer and the transparent contact) redundant and detrimental. Through SCAPS simulation and impedance measurements, the ZnSnO/AZO interface impact on the Cd-free kesterite solar cells’ performances has been investigated, highlighting its leading role in achieving an effective charge extraction and the detrimental effect of the i-ZnO layer. With this approach, a solar cell based on an architecture simpler and more eco-friendly than the conventional one has been produced with comparable efficiencies.

The development of efficient and stable earth-abundant water oxidation catalysts is vital for economically feasible water-splitting systems. Cobalt phosphate (CoPi)-based catalysts belong to the relevant class of nonprecious electrocatalysts studied for the oxygen evolution reaction (OER). In this work, an in-depth investigation of the electrochemical activation of CoPi-based electrocatalysts by cyclic voltammetry (CV) is presented. Atomic layer deposition (ALD) is adopted because it enables the synthesis of CoPi films with cobalt-to-phosphorous ratios between 1.4 and 1.9. It is shown that the pristine chemical composition of the CoPi film strongly influences its OER activity in the early stages of the activation process as well as after prolonged exposure to the electrolyte. The best performing CoPi catalyst, displaying a current density of 3.9 mA cm-2 at 1.8 V versus reversible hydrogen electrode and a Tafel slope of 155 mV/dec at pH 8.0, is selected for an in-depth study of the evolution of its electrochemical properties, chemical composition, and electrochemical active surface area (ECSA) during the activation process. Upon the increase of the number of CV cycles, the OER performance increases, in parallel with the development of a noncatalytic wave in the CV scan, which points out to the reversible oxidation of Co2+ species to Co3+ species. X-ray photoelectron spectroscopy and Rutherford backscattering measurements indicate that phosphorous progressively leaches out the CoPi film bulk upon prolonged exposure to the electrolyte. In parallel, the ECSA of the films increases by up to a factor of 40, depending on the initial stoichiometry. The ECSA of the activated CoPi films shows a universal linear correlation with the OER activity for the whole range of CoPi chemical composition. It can be concluded that the adoption of ALD in CoPi-based electrocatalysis enables, next to the well-established control over film growth and properties, to disclose the mechanisms beh

Electrodeposited cobalt phosphate has been reported in the literature as a robust alternative to noble metal-based electrocatalysts for the O2 evolution reaction. In parallel, atomic layer deposition (ALD) has been acknowledged as a key technology for the preparation of thin films for energy applications. With the present work, the authors have addressed the preparation of cobalt phosphate thin films by a plasma-assisted ALD process. The process developed consists of cobaltocene (step A) and trimethyl phosphate (step C) exposures alternated by O2 plasma (steps B and D) in an ABCD fashion. The process shows a linear growth with a growth per cycle of 1.12 ± 0.05 Å at 300 °C and no nucleation delay. The ALD saturation behavior has been demonstrated for each dosing step, and the process shows minimal inhomogeneity on 100 mm diameter wafers in terms of film thickness (<1.0%) and refractive index (<0.5%). The chemical characterization of the layers deposited shows that the composition is close to the stoichiometric (Co3.1P2O8.3 for a deposition temperature of 200 °C) and the oxidation states of cobalt and phosphorus and agrees with those reported in the literature. The cobalt-to-phosphorous ratio has been found to correlate with the values of absorption coefficient (k) and refractive index (n) of the layers. Furthermore, the authors have gained insights into the surface reactions occurring during each ALD step by quadrupole mass spectrometry investigation. The results suggest that cobaltocene undergoes associative adsorption and the cyclopentadienyl ligands are removed during subsequent O2 plasma exposure. Moreover, the authors have indirectly identified cyclopentadienone as an intermediate of the oxidation and removal of cyclopentadienyl ligand. On the other hand, the trimethyl phosphate dosing is characterized by chemisorption via the elimination of methanol.

Alcohol electrolysis using polymeric membrane electrolytes is a promising route for storing excess renewable energy in hydrogen, alternative to the thermodynamically limited water electrolysis. By properly choosing the ionic agent (i.e. H+ or OH−) and the catalyst support, and by tuning the catalyst structure, we developed membrane-electrode-assemblies which are suitable for cost-effective and efficient alcohol electrolysis. Novel porous electrodes were prepared by Atomic Layer Deposition (ALD) of Pt on a TiO2-Ti web of microfibers and were interfaced to polymeric membranes with either H+ or OH− conductivity. Our results suggest that alcohol electrolysis is more efficient using OH− conducting membranes under appropriate operation conditions (high pH in anolyte solution). ALD enables better catalyst utilization while it appears that the TiO2-Ti substrate is an ideal alternative to the conventional carbon-based diffusion layers, due to its open structure. Overall, by using our developmental anodes instead of commercial porous electrodes, the performance of the alcohol electrolyser (normalized per mass of Pt) can be increased up to ∼30 times.

Electrodeposited cobalt phosphate has been reported as a valid alternative to noble metals as an electrocatalyst for the Oxygen Evolution Reaction (OER). In parallel, Atomic Layer Deposition (ALD) is increasingly being used in (photo)electrocatalytic applications. In this contribution we report on the electrocatalytic activity towards OER of ALD-prepared cobalt phosphate thin films. The selected ALD approach enables tuning of the Co-to-P atomic ratio, which is found to significantly affect the activity of the prepared electrocatalyst. Specifically, concurrently with a Co-to-P ratio increase from 1.6 to 1.9, the current density for OER increases from 1.77 mA/cm2 at 1.8 V vs. RHE (Reversible Hydrogen Electrode) to 2.89 mA/cm2 at 1.8 V vs. RHE. Moreover the sample with a Co-to-P ratio of 1.9 has superior performance when compared to electrodeposited cobalt phosphate thin films reported in the literature.