Characterization of an Insoluble and Soluble Form of Melanin Produced by Streptomyces cavourensis SV 21, a Sea Cucumber Associated Bacterium

Melanin is a widely distributed and striking dark-colored pigment produced by countless living organisms. Although a wide range of bioactivities have been recognized, there are still major constraints in using melanin for biotechnological applications such as its fragmentary known chemical structure and its insolubility in inorganic and organic solvents. In this study, a bacterial culture of Streptomyces cavourensis SV 21 produced two distinct forms of melanin: (1) a particulate, insoluble form as well as (2) a rarely observed water-soluble form. The here presented novel, acid-free purification protocol of purified particulate melanin (PPM) and purified dissolved melanin (PDM) represents the basis for an in-depth comparison of their physicochemical and biological properties, which were compared to the traditional acid-based precipitation of melanin (AM) and to a synthetic melanin standard (SM). Our data show that the differences in solubility between PDM and PPM in aqueous solutions may be a result of different adjoining cation species, since the soluble PDM polymer is largely composed of Mg2+ ions and the insoluble PPM is dominated by Ca2+ ions. Furthermore, AM shared most properties with SM, which is likely attributed to a similar, acid-based production protocol. The here presented gentler approach of purifying melanin facilitates a new perspective of an intact form of soluble and insoluble melanin that is less chemical altered and thus closer to its original biological form

Layer-Thickness-Dependent Work Function of MoS2 on Metal and Metal Oxide Substrates

Transition metal dichalcogenides, such as molybdenum disulfide (MoS2), have unique electronic and optoelectronic properties that are often altered by environmental effects, particularly substrate or contact materials. Understanding these effects is important for device design and engineering. There is limited information concerning how MoS2 interacts with 3D semiconductors such as metal oxides. This work demonstrates the influence of substrate material and MoS2 layer thickness on the work function of exfoliated MoS2 flakes. Kelvin probe force microscopy is used to probe the work function of MoS2 on titanium oxide (TiOx), molybdenum oxide (MoOx), and gold (Au). We find that TiOx based substrates yield a lower MoS2 work function than MoOx and Au for various MoS2 thicknesses, and that the screening lengths for each substrate are larger than 5 nm. By reporting the work function variation of MoS2 on these substrates, this study aims to provide important insights into device design and contact engineering

Two-Dimensional Absorbers for Solar Windows: A Simulation

In the future, many modern buildings may rely on solar windows for energy production. Large buildings often have glass facades that have the potential to convert sunlight to electrical power. The standard photovoltaic materials used today are bulky and not transparent, making them poor candidates for solar windows. Transition metal dichalcogenides (TMDCs) and other two-dimensional absorbers are a good alternative because of their unique properties and high transparency at the monolayer and few-layer regime. This work shows the potential for TMDC-based solar windows by simulating the transmission, quantum efficiency, current density, and colour appearance of different solar cell configurations. Different contacts were investigated, along with the influence of contact thickness, to demonstrate colour-neutral solar cells. In addition, four TMDC materials were compared: MoS2, MoSe2, WS2, and WSe2. Colour-neutral solar cells with transparencies of 35 % to 55 % are presented, where a current density of 8.33 mA/cm2 was calculated for a solar cell with a 5-nm absorbing layer of MoSe2. While there are still challenges to overcome in terms of production, our simulations show that it is possible to use TMDCs for colour-neutral solar windows and act as a guideline for further research

Optoelectronic Properties of MoS2 in Proximity to Carrier Selective Metal Oxides

Transition metal dichalcogenides are an exciting class of new absorber materials for photovoltaic applications due to their unique optoelectronic properties in the single to few-layer regime. In recent years, these materials have been intensively studied, often utilizing conventional substrates such as sapphire and silicon dioxide on silicon. This study investigates the optical properties of molybdenum disulfide (MoS2) mono-, bi-, and multilayer films prepared by flake exfoliation and atomic layer deposition (ALD). These films are transferred to different photovoltaic relevant carrier-selective contacts, such as titanium oxide, titanium–titanium oxide, molybdenum oxide, and silicon-silicon dioxide reference substrates. Raman and photoluminescence (PL) spectra of single-crystalline exfoliated MoS2 flakes and ALD-grown MoS2 films on different substrates are compared in order to investigate the influence of the different contact materials on the corresponding optical transitions in MoS2. It is demonstrated that the different substrates influence the Raman and PL spectra of MoS2 layers due to doping and charge transfer effects, and similar effects are observed in both the exfoliated single-crystalline flakes and ALD-grown MoS2 layers

Tunable Photovoltaics: Adapting Solar Cell Technologies to Versatile Applications

Solar photovoltaics (PV) offer viable and sustainable solutions to satisfy the growing energy demand and to meet the pressing climate targets. The deployment of conventional PV technologies is one of the major contributors of the ongoing energy transition in electricity power sector. However, the diversity of PV paradigms can open different opportunities for supplying modern systems in a wide range of terrestrial, marine, and aerospace applications. Such ubiquitous and versatile applications necessitate the development of PV technologies with customized design capabilities. This involves multifunctional characteristics such as aesthetic appearance, visual comfort, and heat insulation. To enable on-demand adaptation to the requirements of distributed applications, tunable solar cells (SC) feature exceptional degrees of freedom in the manipulation of their intrinsic properties via adjusted materials engineering. The pertinent tuning abilities include but are not limited to bandgap energy, transparency, color, and thermal management. In this review, the main principles of different tuning approaches are specified and an overview of relevant concepts of tunable SC technologies is presented. Then, the recent integrations of cutting-edge tunable PV adapted to versatile applications are systematically summarized. In addition, current challenges and insightful perspectives into potential future opportunities for omnipresent tunable PV are discussed

Inside Back Cover: Tunable Photovoltaics: Adapting Solar Cell Technologies to Versatile Applications

Tunable Photovoltaics In article number 2200713, Hosni Meddeb and co-workers present a comprehensive review on tunable photovoltaics with customized design capabilities covering different aspects such as bandgap energy, transparency and color attributes. The multifunctional characteristics including appearance, visual comfort and thermal management along with power generation enable the adaptation of solar cell technologies in versatile applications. Perspectives to guide relevant future integration scenarios are explored