ZOOM SEMINAR
Monday, july 6, 2020 at 14:00
Photovoltaics with 2D Materials: Optoelectronic Aspects of Large-Scale MoS2/Si Heterojunctions

Omer Luria
M.Sc student of Prof. Abraham Kribus and Dr. Ariel Ismach

Photovoltaics (PV) is the leading technology for solar electricity generation, with attractive levelized energy cost and a direct electrical output. Current commercial PV materials have already realized their potential in terms of conversion efficiency, and therefore the research community is in constant search of new materials. Since the rediscovery of graphene, two-dimensional (2D) layered materials have gained interest as the next generation of material science and nanotechnology. Among those, atomically thin transition metal dichalcogenides (TMDs, the group MX2 where M=Mo,W,In,Ta , X=S,Se etc) show interesting optoelectronic properties. Those properties include high absorption and convenient direct band gap in the solar spectrum, making them very promising for photovoltaic conversion. However, the commercial-scale synthesis of these materials is done by chemical vapor deposition that results in non-uniform and discontinuous coverage on the substrate, especially on the scale of monolayers. In this work, monolayer (1L) CVD-grown MoS2 is investigated. Spectroscopic methods such as Ellipsometry, Reflectometry, Raman scattering and Photoluminescence are used to investigate its structural and optical properties. By combining innovative simulation, optimization and data analysis software written in open-source Python, both intrinsic material properties and device performance can be estimated. Optical models that account for non-uniform surface coverage allow extending the common methodology and applying it also in large scales, where the inhomogeneity of the growth process is almost intrinsic.
A large-scale photovoltaic device based on a 1L-MoS2/Si heterojunction was fabricated and characterized. A combined optoelectronic analysis was used to estimate both the global performance merit and the power distribution among the various loss mechanisms. The optical analysis allows the separation of different contributions to the total measured power, which is useful for estimating the potential of MoS2 and TMDs in general in future devices as well. The results clearly show that the intrinsic ability of MoS2 to absorb and utilize solar energy is superior comparing to commercial 3D semiconductor materials. This work exhibits another milestone towards the integration of 2D materials in existing and novel technologies.
~~Join Zoom Meeting
https://zoom.us/j/96584758181?pwd=WC9PMXdsYzJ3NFdEN2Q5ZUtOZEVjdz09 The meeting will be recorded and made available on the School’s site.
 

Internal Mechanics of the Wrist in the Sagittal versus Dart Throwing Motion

Plane in Adult and Elder Models: Finite Element Analyses

Vered Mahpari, Masters Student

Under the supervision of Dr. Sigal Portnoy and Prof. Meital Zilberman

Most clinical treatments for an injured wrist such as distal radius fracture, concentrate on movement in the sagittal plane. The rotation of the proximal carpal bones is smaller while moving the wrist in a Dart Throwing Motion (DTM) than in other planes. This might prove advantageous during rehabilitation exercises that incorporate the DTM plane by reducing pain. However, the stresses between the Radius and the carpal bones in these two planes have not been compared and might differ between adult and elder individuals. This paper compares the contact stresses between the Radius and two carpal bones (the Scaphoid and the Lunate) between two wrist positions: extension and radial-extension (DTM) and between adult and elder models. A healthy wrist of a 40 year old female was scanned using Magnetic Resonance Imaging in two wrist positions (extension, radial-extension). The scans were transformed into three dimensional (3D) models and meshed using ScanIP (Simpleware Ltd., Exeter, UK) software. Finite Element Analyses in each position of the wrist were conducted for both adult and elder models (using MSC Nastran software, MSC Software Corporation, CA, USA), which differentiate by the mechanical properties of the ligaments. In the adult model, the average contact stresses between the distal Radius and the proximal carpal bones were higher in Extension (8.40MPa Radius-Scaphoid and 5.34MPa Radius-Lunate) compared to Radial-Extension (2.82MPa Radius-Scaphoid and 3.06MPa Radius-Lunate). In the elder model, the average contact stresses between the distal Radius and the proximal carpal bones were higher in Extension (8.45MPa Radius-Scaphoid and 5.12MPa Radius-Lunate) compared to Radial-Extension (0.97MPa Radius-Scaphoid and 4.14MPa Radius-Lunate). The lower stresses found in Radial-Extension position might be advantageous in wrist rehabilitation due to possible reduced pain. According to the four finite element analyses presented in this thesis, this conclusion is relevant to both adults and elder individuals.