E-Theses

Limiting Efficiency Of Perovskite Solar Cells

2016-10-28T05:09:22Z

Limiting Efficiency Of Perovskite Solar Cells Ugwoke, Luke Chinedu The power conversion efficiency of perovskite solar cells has risen from as low as 3.8% to as high as 19.3% in just five years with yet a projected value of over 20% in the next few years by experimentalists. Such a tremendous breakthrough is one of its kind in photo-voltaic research with thin film solar cells as the only major competitor. The light harvesting layer in these new devices has a crystalline structure called the perovskite structure which is capable of absorbing photons in both the visible and near infra-red regions of the solar radiation spectrum. In this study, we carried out theoretical studies based on the detailed balance theory originally proposed by Shockley and Queisser, and on a semi-emperical approach based on measured optical absorption spectrum of the three most widely used perovskite absorbers: CH3 NH3 SnI3 , CH3 NH3 PbI3 , and CH3 NH3 PbI3-x Clx . We arrived at an upper conversion efficiency limit for a single planar hetero-junction(PHJ) perovskite solar cell with anti-reflection capabilities considering radiative losses as the only carrier loss mechanism within the cell. The limiting efficiency was found to be 29.2% for CH3 NH3 PbI3 , 27.5% for CH3 NH3 PbI3-x Clx , and 24.8% for CH3 NH3 SnI3 under AM1.5 solar spectrum. Issues such as the effect of exciton diffusion length and absorber thickness on the efficiency are also discussed.

Development Of A Correction Term For The Kinetic Energy Density Functional

2016-10-28T05:09:24Z

Development Of A Correction Term For The Kinetic Energy Density Functional Nwankwo, Udoka Density functional theory (DFT) is a useful theoretical and computational tool for electronic structure calculations, which form the basis for the classification of materials into conductors, semiconductors or insulators. DFT started with a crude approximation by Thomas and Fermi (TF theory) which calculated the kinetic energy of electrons using the so-called local density approximation (LDA). Although TF is computationally inexpensive, it provides a poor numerical result due to a lack of understanding of the density dependence of the kinetic energy. Another approximation to the kinetic energy is the von-Weizsacker (vW) term, which greatly improves the TF theory, yet the full functional form of the kinetic energy remains unknown. We seek to develop a supplemental term to the kinetic energy density functional and compute corrections to the Thomas-Fermi-von-Weizsacker kinetic energy of closed shell atoms in order to improve its accuracy.

Molecular Dynamics Simulation Of Transport Of Encapsulated Drug Through A Lipid Bilayer

2016-10-28T05:09:23Z

Molecular Dynamics Simulation Of Transport Of Encapsulated Drug Through A Lipid Bilayer Ibrahim, Buba Gaba Most anticancer drugs are polar, cytotoxic and have complicated structures which cause difficulty in their penetration through the cell membrane. This presents a serious problem in chemotherapy. Is it possible to use carbon nanotubes (CNTs) as intracellular drug delivery agents to concomitantly mininmize side effects and maximize therapeutic effect? Although previous experimental and simulation studies have demonstrated that CNTs are able to translocate through cell membrane, the cell penetration mechanisms are not well understood. In this study, we used molecular dynamics simulation to examine the trans- port of an anticancer drug, Cisplatin, (with and without encapsulation in a CNT) across a solvated DPPC (1,2-DIPALMITOYLPHOSPHATIDYLCHOLINE) lipid bilayer which represents the cell membrane.

Performance Optimization Of Tin Halide Perovskite Solar Cells Via Numerical Simulation

2016-10-28T05:09:16Z

Performance Optimization Of Tin Halide Perovskite Solar Cells Via Numerical Simulation Amu, Tochukwu Loreta Organic-inorganic hybrid perovskite solar cells have attracted great attention in the photovoltaic research community in recent years due to its ease of processing, low cost of production, superb light-harvesting characteristics, and relatively high efficiency which make it more preferable over other existing solar cell materials. Lead-based perovskites (CH3NH3PbX3, X= Cl, I, Br) solar cells have recently attained a high efficiency of ~19.3% which far surpasses the efficiencies of most thin film and organic solar cells. Therefore, the presence of lead, which is a toxic material in these solar cells poses serious challenge to our health and environment. ‘Tin’ is non-toxic and stands as a replacement to ‘lead’ for commercial purposes. Thus, there is a drive to use non-toxic materials such as tin-based perovskites. Unfortunately, the tin-based perovskite solar cells recently produced have low efficiencies (< 6.4% ). In order to improve the performance of tin-based perovskite solar cells, a numerical simulation was done. First, known experimental results were reproduced. Based on the work reproduced we developed a new configuration with a reduced acceptor doping concentration of the absorber layer which showed an increase in efficiency > 18%. A device simulator, the Solar Cell Capacitance Simulator (SCAPS) was used to solve the poisson and hole and electron continuity equations in order to obtain information concerning the device properties of the tin-based perovskite (CH3NH3SnI3) solar cells.