Solar Cell Silicon: Properties, Photovoltaics, and Other Applications
Sponsored by: TMS Extraction and Processing Division, TMS: Recycling and Environmental Technologies Committee, TMS: Materials Characterization Committee
Program Organizers: Shadia Ikhmayies; Neale Neelameggham, IND LLC
Monday 2:30 PM
February 24, 2020
Room: Miramar
Location: Marriott Marquis Hotel
Session Chair: Shadia Ikhmayies, Isra University
2:30 PM Introductory Comments
2:35 PM
First Principles Modeling of Water-induced Polymer Encapsulant Degradation in Silicon Modules: Arun Kumar Mannodi Kanakkithodi1; Rishi Kumar2; David Fenning2; Maria Chan1; 1Argonne National Laboratory; 2University of California, San Diego
An outstanding issue in Si photovoltaic modules is the accelerated degradation caused by the presence of moisture, which leads to interfacial instability, encapsulant decomposition and corrosion at contacts. In this work, we use density functional theory (DFT) to model the structure and degradation mechanisms of ethylene vinyl acetate (EVA), the most common polymer encapsulant used in Si PV modules. Infrared active modes computed for EVA crystalline structures match well with reported experiments. The Nudged Elastic Band (NEB) method is applied to model decomposition mechanisms of EVA, with and without the presence of moisture; computed energy barriers show a preference for acetic acid formation and are lowered by the presence of a solvent or catalyst such as a proton or hydroxyl ion. This systematic study leads to a clear picture of the hydrolysis-driven decomposition of EVA in terms of energetically favorable mechanisms, possible intermediate structures, and IR signatures of reaction products.
2:55 PM
Thermodynamic Properties of Si-P Binary System: Shadia Ikhmayies1; 1Al Isra University
Phosphorous (P) is a doping element of silicon to get n-type conductivity, where P-doped silicon is used important in optoelectronic industries. So studying the thermodynamic properties of Si-P system is interesting for silicon solar cell industry, and other silicon based technologies. In this work thermodynamic properties of Si-P binary system were determined using Thermo-Calc software at a pressure of 1 bar. Activity, Gibbs free energy, enthalpy, and entropy were plotted against temperature and/or composition and discussed on the light of the phase diagram.
3:15 PM
Using Thermo-calc Software to Deduce the Thermodynamic Properties of Si-B Binary System: Shadia Ikhmayies1; 1Al Isra University
Thermodynamic properties of the Si-B binary system were calculated using thermo-Calc software at a pressure of 1 bar. Gibbs free energy, enthalpy, entropy, and activity were calculated and plotted against temperature and composition. Gibbs free energy curves for all phases were discussed and found to be consistent with phase diagram. It is found that Gibbs free energy becomes more negative with temperature, and it shows minima at certain composition values for different phases. Enthalpy curves for all phases are plotted with composition, and they are consistent with Gibbs free energy curves, then plotted against temperature and showed increase from negative values to positive values. Entropy and activity curves for all phases were plotted against composition and temperature and thoroughly discussed. The largest value of boron activity is about 0.49, and the curves shown maxima then a monotonic decrease with temperature, where activity of boron becomes about 0.03.
3:35 PM
Dislocation-based Thermodynamic Models of V-pits Formation and Strain Relaxation in InGaN/GaN Epilayers on Si Substrates: Khaled Khafagy1; Tarek Hatem2; Salah Bedair1; 1North Carolina State University; 2The British University in Egypt
The growth of III-N such InGaN on Si substrates is inherently difficult and leads to high-defects densities. Such defects act as scattering centers that impact the minority carrier lifetime and therefore efficiency. Furthermore, generation of high-defects densities in the interfaces between III-N layers and Si substrate lead to higher generation of V-shaped pits densities on the top surface. V-pits generates rough surfaces that directly affects the performance and the efficiency of the device. In the current work, we present a thermodynamic based-model that considers the energy balance between the strain energy in the III-N epitaxial layers, the dislocation energy that forms a V-pit, and the strain energy relieved to nucleate a V-pit in order to achieve thermal equilibrium in the system. The results of the model are compared to experimental observations of the growth of semi-bulk InGaN/GaN structure.