Corsin Battaglia

High-efficiency crystalline silicon solar cells: status and perspectives

With a global market share of about 90%, crystalline silicon is by far the most important photovoltaic technology today. This article reviews the dynamic field of crystalline silicon photovoltaics from a device-engineering perspective. First, it discusses key factors responsible for the success of the classic dopant-diffused silicon homojunction solar cell. Next it analyzes two archetypal high-efficiency device architectures – the interdigitated back-contact silicon cell and the silicon heterojunction cell – both of which have demonstrated power conversion efficiencies greater than 25%. Last, it gives an up-to-date summary of promising recent pathways for further efficiency improvements and cost reduction employing novel carrier-selective passivating contact schemes, as well as tandem multi-junction architectures, in particular those that combine silicon absorbers with organic–inorganic perovskite materials.

Molybdenum oxide MoOx: A versatile hole contact for silicon solar cells

This letter examines the application of transparent MoOx (xu2009<u20093) films deposited by thermal evaporation directly onto crystalline silicon (c-Si) to create hole-conducting contacts for silicon solar cells. The carrier-selectivity of MoOx based contacts on both n- and p-type surfaces is evaluated via simultaneous consideration of the contact recombination parameter J0c and the contact resistivity ρc. Contacts made to p-type wafers and p+ diffused regions achieve optimum ρc values of 1 and 0.2 mΩ·cm2, respectively, and both result in a J0c of ∼200 fA/cm2. These values suggest that significant gains can be made over conventional hole contacts to p-type material. Similar MoOx contacts made to n-type silicon result in higher J0c and ρc with optimum values of ∼300 fA/cm2 and 30 mΩ·cm2 but still offer significant advantages over conventional approaches in terms of contact passivation, optical properties, and device fabrication.

Design Guidelines for High-Performance Particle-Based Photoanodes for Water Splitting: Lanthanum Titanium Oxynitride as a Model.

Semiconductor powders are perfectly suited for the scalable fabrication of particle-based photoelectrodes, which can be used to split water using the sun as a renewable energy source. This systematic study is focused on variation of the electrode design using LaTiO2 N as a model system. We present the influence of particle morphology on charge separation and transport properties combined with post-treatment procedures, such as necking and size-dependent co-catalyst loading. Five rules are proposed to guide the design of high-performance particle-based photoanodes by adding or varying several process steps. We also specify how much efficiency improvement can be achieved using each of the steps. For example, implementation of a connectivity network and surface area enhancement leads to thirty times improvement in efficiency and co-catalyst loading achieves an improvement in efficiency by a factor of seven. Some of these guidelines can be adapted to non-particle-based photoelectrodes.

The Origin of the Catalytic Activity of a Metal Hydride in CO2 Reduction

Atomic hydrogen on the surface of a metal with high hydrogen solubility is of particular interest for the hydrogenation of carbon dioxide. In a mixture of hydrogen and carbon dioxide, methane was markedly formed on the metal hydride ZrCoHx in the course of the hydrogen desorption and not on the pristine intermetallic. The surface analysis was performed by means of time-of-flight secondary ion mass spectroscopy and near-ambient pressure X-ray photoelectron spectroscopy, for the in situ analysis. The aim was to elucidate the origin of the catalytic activity of the metal hydride. Since at the initial stage the dissociation of impinging hydrogen molecules is hindered by a high activation barrier of the oxidised surface, the atomic hydrogen flux from the metal hydride is crucial for the reduction of carbon dioxide and surface oxides at interfacial sites.

A Generalized Theory Explains the Anomalous Suns–

Suns-Voc measurements exclude parasitic series resistance effects and are, therefore, frequently used to study the intrinsic potential of a given photovoltaic technology. However, when applied to a-Si/c-Si heterojunction (SHJ) solar cells, the Suns-Voc curves often feature a peculiar turnaround at high illumination intensities. Generally, this turn-around is attributed to extrinsic Schottky contacts that should disappear with process improvement. In this paper, we demonstrate that this voltage turnaround may be an intrinsic feature of SHJ solar cells, arising from the heterojunction (HJ), as well as its associated carrier-transport barriers, inherent to SHJ devices. We use numerical simulations to explore the full current-voltage (J-V) characteristics under different illumination and ambient temperature conditions. Using these characteristics, we establish the voltage and illumination-intensity bias, as well as temperature conditions necessary to observe the voltage turnaround in these cells. We validate our turnaround hypothesis using an extensive set of experiments on a high-efficiency SHJ solar cell and a molybdenum oxide (MoOx) based hole collector HJ solar cell. Our work consolidates Suns-Voc as a powerful characterization tool for extracting the cell parameters that limit efficiency in HJ devices.

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We report on a particularly stable 3 V all-solid-state sodium–ion battery built using a closo-borate based electrolyte, namely Na2(B12H12)0.5(B10H10)0.5. Battery performance is enhanced through the creation of an intimate cathode–electrolyte interface resulting in reversible and stable cycling with a capacity of 85 mA h g−1 at C/20 and 80 mA h g−1 at C/5 with more than 90% capacity retention after 20 cycles at C/20 and 85% after 250 cycles at C/5. We also discuss the effect of cycling outside the electrochemical stability window and show that electrolyte decomposition leads to faster though not critical capacity fading. Our results demonstrate that owing to their high stability and conductivity closo-borate based electrolytes could play a significant role in the development of a competitive all-solid-state sodium–ion battery technology.

Response of Si Heterojunction Solar Cells

Ultra-high salt concentration has recently been reported to extend the kinetic stability of aqueous electrolytes up to 3 V. However, the low ionic conductivity of these systems makes them unsuitable for high power devices such as supercapacitors. In this study, an 8 mol kg−1 NaTFSI aqueous electrolyte is reported that displays a high stability of 1.8 V on activated carbon during a stringent stability test and a conductivity of 48 mS cm−1 at 20 °C, the latter being comparable to the one of state-of-the-art acetonitrile-based non-aqueous electrolytes. A 1.8 V carbon/carbon supercapacitor employing 8 mol kg−1 NaTFSI displays a high maximum energy density of 14.4 W h kg−1 on the activated carbon mass level and stable cycling for 100u2006000 cycles. By addition of the redox additive potassium iodide to the electrolyte, the maximum specific energy could be increased to an extremely high value of 37.8 W h kg−1, comparable to the performance of the current generation of commercial non-aqueous supercapacitors.

A stable 3 V all-solid-state sodium–ion battery based on a closo-borate electrolyte

Solar-powered electrochemical production of hydrogen through water electrolysis is an active and important research endeavor. However, technologies and roadmaps for implementation of this process do not exist. In this perspective paper, we describe potential pathways for solar-hydrogen technologies into the marketplace in the form of photoelectrochemical or photovoltaic-driven electrolysis devices and systems. We detail technical approaches for device and system architectures, economic drivers, societal perceptions, political impacts, technological challenges, and research opportunities. Implementation scenarios are broken down into short-term and long-term markets, and a specific technology roadmap is defined. In the short term, the only plausible economical option will be photovoltaic-driven electrolysis systems for niche applications. In the long term, electrochemical solar-hydrogen technologies could be deployed more broadly in energy markets but will require advances in the technology, significant cost reductions, and/or policy changes. Ultimately, a transition to a society that significantly relies on solar-hydrogen technologies will benefit from continued creativity and influence from the scientific community.