A method for producing conductive graphene biopolymer nanofibrous fabrics by exploitation of an ionic liquid dispersant in electrospinning

Owing to its high conductivity, graphene has been incorporated into polymeric nanofibers to create advanced materials for flexible electronics, sensors and tissue engineering. Typically, these graphene-based nanofibers are prepared by electrospinning synthetic polymers, whereas electrospun graphene-biopolymer nanofibers have been rarely reported due to poor compatibility of graphene with biopolymers. Herein, we report a new method for the preparation of graphene-biopolymer nanofibers using the judicious combination of an ionic liquid and electrospinning. Cellulose acetate (CA) has been used as the biopolymer, graphene oxide (GO) nanoparticles as the source of graphene and 1-butyl-3-methylimidazolium chloride ([BMIM]Cl) as the ionic liquid (IL) to create CA-[BMIM]Cl-GO nanofibers by electrospinning for the first time. Moreover, we developed a new route to convert CA-[BMIM]Cl-GO nanofibers to reduced GO nanofibers using hydrazine vapor under ambient conditions to enhance the conductivity of the hybrid nanofibers. The graphene sheets were shown to be uniformly incorporated in the hybrid nanofibers and only 0.43 wt% of GO increase the conductivity of CA-[BMIM]Cl nanofibers by more than four orders of magnitude (from 2.71× 10−7 S/cm to 5.30 × 10−3 S/cm). This ultra-high enhancement opens up a new route for conductive enhancement of biopolymer nanofibers to be used in smart (bio) electronic devices

Cu2ZnSnS4 monograin layer solar cells for flexible photovoltaic applications

<h3>Abstract</h3><p>Monograin powder technology is one possible path to developing sustainable, lightweight, flexible, and semi-transparent solar cells, which might be ideal for integration with various building and product elements. In recent years, the main research focus of monograin technology has centered around understanding the synthesis and optoelectronic properties of kesterite-type absorber materials. Among these, Cu2ZnSnS4 (CZTS) stands out as a promising solar cell absorber due to its favorable optical and electrical characteristics. CZTS is particularly appealing as its constituent elements are abundant and non-toxic, and it currently holds the record for highest power conversion efficiency (PCE) among emerging inorganic thin-film PV candidates. Despite its advantages, kesterite solar cells' PCE still falls significantly behind the theoretical maximum efficiency due to the large <i>V</i>OC deficit. This review explores various strategies aimed at improving <i>V</i>OC losses to enhance the overall performance of CZTS monograin layer solar cells. It was found that low-temperature post-annealing of CZTS powders reduced Cu–Zn disordering, increasing <i>E</i>g by ∼100 meV and <i>V</i>OC values; however, achieving the optimal balance between ordered and disordered regions in kesterite materials is crucial for enhancing photovoltaic device performance due to the coexistence of ordered and disordered phases. CZTS alloying with Ag and Cd suppressed non-radiative recombination and increased short-circuit current density. Optimizing Ag content at 1% reduced CuZn antisite defects, but higher Ag levels compensated for acceptor defects, leading to reduced carrier density and decreased solar cell performance. Co-doping with Li and K resulted in an increased bandgap (1.57 eV) and improved <i>V</i>OC, but further optimization is required due to a relatively large difference between measured and theoretical <i>V</i>OC. Heterojunction modifications led to the most effective PCE improvement in CZTS-based solar cells, achieving an overall efficiency of 12.06%.</p&gt

Enhanced photocatalytic activity of chemically deposited ZnO nanowires using doping and annealing strategies for water remediation

Water pollution represents one of the most challenging ecological threats humankind faces nowadays, resulting in the fast growing development of the heterogeneous photocatalysis using ZnO nanowires. A typical approach to improve the photocatalytic activity consists in achieving their extrinsic doping with group-III elements, but the reasons accounting for the resulting, modified photocatalytic processes are multifactorial and still under debate. In this work, we investigate the effect of the Al and Ga doping of ZnO nanowires grown by chemical bath deposition and of the thermal annealing under oxygen atmosphere on their photocatalytic activity and establish the dependence of the photocatalytic processes on their structural morphology, dimensions, dopant-induced defects, surface properties, and optical absorption and emission. We reveal that the photocatalytic processes strongly depend on the nature of dopants and are systematically enhanced after thermal annealing. The photocatalytic activity of annealed, Al-doped ZnO nanowires is found to be more efficient, through the direct action of holes besides the efficient action of radicals in the degradation process of organic dyes. These findings show the significance of decoupling the intricate contributions to the photocatalytic activity of ZnO nanowires when the extrinsic doping is used and of thoroughly selecting the nature of dopants

Rational design of highly efficient flexible and transparent p-type composite electrode based on single-walled carbon nanotubes

Transparent electrodes are of great importance in electronics and energy technologies. At present, transparent conductive oxides are mainly n-type conductors dominating the market and have restricted the technological advancements. Single-walled carbon nanotubes (SWCNTs) have recently emerged as promising p-type transparent conductor owing to their superior hole mobility, conductivity, transparency, flexibility and possibility to tune the work function. Here, we develop a novel rational design of p-type flexible transparent conductive film (TCF) based on SWCNTs combined with poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), molybdenum oxide and SWCNT fibers. In a configuration of SWCNTs-MoO3-PEDOT:PSS/SWCNT fibers, we achieved a record equivalent sheet resistance of 17 Ω/sq with a transmittance of 90% at 550 nm and a high degree of flexibility. We demonstrate that our solar cells developed on the basis of the proposed electrode and hydrogenated amorphous silicon (a-Si:H) yield an outstanding short-circuit current density of Jsc = 15.03 mA/cm2 and a record power conversion efficiency of PCE = 8.8% for SWCNTs/a-Si:H hybrid solar cells. We anticipate that this novel rationally designed p-type TCF opens a new avenue in widespread energy technologies, where high hole conductivity and transparency of the material are prerequisites for their successful implementation.Peer reviewe

High-Temperature Tribological Performance of Al2O3/a-C:H:Si Coating in Ambient Air

The study investigates thermal stability and high temperature tribological performance of a-C:H:Si diamond-like carbon (DLC) coating. A thin alumina layer was deposited on top of the a-C:H:Si coating to improve the tribological performance at high temperatures. The a-C:H:Si coating and alumina layer were prepared using plasma-activated chemical vapour deposition and atomic layer deposition, respectively. Raman and X-ray photoelectron spectroscopy were used to investigate the structures and chemical compositions of the specimens. The D and G Raman peaks due to sp2 bonding and the peaks corresponding to the trans-polyacetylene (t-Pa) and sp bonded chains were identified in the Raman spectra of the a-C:H:Si coating. Ball-on-disc sliding tests were carried out at room temperature and 400 °C using Si3N4 balls as counter bodies. The a-C:H:Si coating failed catastrophically in sliding tests at 400 °C; however, a repeatable and reproducible regime of sliding with a low coefficient of friction was observed for the Al2O3/a-C:H:Si coating at the same temperature. The presence of the alumina layer and high stress and temperature caused structural changes in the bulk a-C:H:Si and top layers located near the contact area, leading to the modification of the contact conditions, delivering of extra oxygen into the contact area, reduction of hydrogen effusion, and suppression of the atmospheric oxidation

Adhesion of Single-Walled Carbon Nanotube Thin Films with Different Materials

Single-walled carbon nanotubes (SWCNTs) possess extraordinary physical and chemical properties. Thin films of randomly oriented SWCNTs have great potential in many opto-electro-mechanical applications. However, good adhesion of SWCNT films with a substrate material is pivotal for their practical use. Here, for the first time, we systematically investigate the adhesion properties of SWCNT thin films with commonly used substrates such as glass (SiO2), indium tin oxide (ITO), crystalline silicon (C-Si), amorphous silicon (a-Si:H), zirconium oxide (ZrO2), platinum (Pt), polydimethylsiloxane (PDMS), and SWCNTs for self-adhesion using atomic force microscopy. By comparing the results obtained in air and inert Ar atmospheres, we observed that the surface state of the materials greatly contributes to their adhesion properties. We found that the SWCNT thin films have stronger adhesion in an inert atmosphere. The adhesion in the air can be greatly improved by a fluorination process. Experimental and theoretical analyses suggest that adhesion depends on the atmospheric conditions and surface functionalization.Peer reviewe