Physics Commons^™

Investigating New Methods To Develop Perovskite Solar Cells, Amani Hussain Alfaifi

Electronic Theses and Dissertations

Discovering the potential of organic-inorganic metal halide perovskites (MHP) as a harvesting material in solar cells has strongly affected the research direction in solar energy. The fascinating optical and electronic properties offered by MHP combined with tremendous effort from scientists around the world have improved the efficiency to about 25% in a decade.

In the first part of the dissertation, we studied the lamination process as a new fabrication method for producing self-encapsulated perovskite solar cells based on laminating half stacks,as opposed to the conventional layer-by-layer method. Our work focused on optimizing the lamination process of complex triple cations perovskite …

Studies Of Initial Growth Of Gan On Inn, Alaa Alnami

Graduate Theses and Dissertations

III-nitride materials have recently attracted much attention for applications in both the microelectronics and optoelectronics. For optoelectronic devices, III-nitride materials with tunable energy band gaps can be used as the active region of devices to enhance the absorption or emission. A such material is indium nitride (InN), which along with gallium nitride (GaN) and aluminum nitride (AlN) embody the very real promise of forming the basis of a broad spectrum, a high efficiency solar cell. One of the remaining complications in incorporating InN into a solar cell design is the effects of the high temperature growth of the GaN crystal …

Bandgap Profiling In Cigs Solar Cells Via Valence Electron Energy-Loss Spectroscopy, Julia I. Deitz, Shankar Karki, Sylvain X. Marsillac, Tyler J. Grassman

Electrical & Computer Engineering Faculty Publications

A robust, reproducible method for the extraction of relative bandgap trends from scanning transmission electron microscopy (STEM) based electron energy-loss spectroscopy (EELS) is described. The effectiveness of the approach is demonstrated by profiling the bandgap through a CuIn_1-xGa_xSe₂ solar cell that possesses intentional Ga/(In + Ga) composition variation. The EELS-determined bandgap profile is compared to the nominal profile calculated from compositional data collected via STEM-based energy dispersive X-ray spectroscopy. The EELS based profile is found to closely track the calculated bandgap trends, with only a small, fixed offset difference. This method, which is particularly advantageous …

Band Offsets At The Interface Between Crystalline And Amorphous Silicon From First Principles, Karol Jarolimek, E. Hazrati, R. A. De Groot, D. A. De Wijs

Center for Applied Energy Research Faculty and Staff Publications

The band offsets between crystalline and hydrogenated amorphous silicon (a−Si∶H) are key parameters governing the charge transport in modern silicon heterojunction solar cells. They are an important input for macroscopic simulators that are used to further optimize the solar cell. Past experimental studies, using x-ray photoelectron spectroscopy (XPS) and capacitance-voltage measurements, have yielded conflicting results on the band offset. Here, we present a computational study on the band offsets. It is based on atomistic models and density-functional theory (DFT). The amorphous part of the interface is obtained by relatively long DFT first-principles molecular-dynamics runs at an elevated temperature …

Reflective Efficiencies Of Materials For Applications Of Bifacial Solar Cells, Michael Metter

Senior Theses

The bifacial solar cell is superior to its monofacial predecessor due to its ability to convert both incident light on top and reflected light from below into energy. The scattering of the reflected light is affected by the property of the material on which it is interacting. To date, little work has been contributed to studying the properties of these materials to determine optimal quantities for bifacial solar cells. In the first experiment, reflective efficiencies compared to the angle of reflection were explored for different grit of sandpaper in order to develop an understanding of how surface texture impacts reflectivity. …

Atmospheric Pressure Chemical Vapor Deposition Of Functional Oxide Materials For Crystalline Silicon Solar Cells, Kristopher Davis

Electronic Theses and Dissertations

Functional oxides are versatile materials that can simultaneously enable efficiency gains and cost reductions in crystalline silicon (c-Si) solar cells. In this work, the deposition of functional oxide materials using atmospheric pressure chemical vapor deposition (APCVD) and the integration of these materials into c-Si solar cells are explored. Specifically, thin oxide films and multi-layer film stacks are utilized for the following purposes: (1) to minimize front surface reflectance without increasing parasitic absorption within the anti-reflection coating(s); (2) to maximize internal back reflectance of rear passivated cells, thereby increasing optical absorption of weakly absorbed long wavelength photons (? > 900 nm); (3) …

Plasmonic Nanostructures For The Absorption Enhancement Of Silicon Solar Cells, Nathan Matthias Burford

Graduate Theses and Dissertations

In this work, computational investigation of plasmonic nanostructures was conducted using the commercial finite element electromagnetics solver Ansys® HFSS. Arrays of silver toroid nanoparticles located on the surface of an amorphous silicon thin-film absorbing layer were studied for particle sizes ranging from 20 nm to 200 nm in outer diameter. Parametric optimization by calculating an approximation of the photocurrent enhancement due to the nanoparticles was performed to determine optimal surface coverage of the nanoparticles. A comparison was made between these optimized nanotoroid arrays and optimized nanosphere arrays based on spectral absorption enhancement and potential photocurrent enhancement in an amorphous silicon …

Making Solar Cells, D. Venkataraman

Nanotechnology Teacher Summer Institutes

Overview of solar energy and photovoltaic cells. Making a cuprous oxide cell activity.

Plasmonic And Photonic Designs For Light Trapping In Thin Film Solar Cells, Liming Ji

Graduate Theses and Dissertations

Thin film solar cells are promising to realize cheap solar energy. Compared to conventional wafer cells, they can reduce the use of semiconductor material by 90%. The efficiency of thin film solar cells, however, is limited due to insufficient light absorption. Sufficient light absorption at the bandgap of semiconductor requires a light path more than 10x the thickness of the semiconductor. Advanced designs for light trapping are necessary for solar cells to absorb sufficient light within a limited volume of semiconductor. The goal is to convert the incident light into a trapped mode in the semiconductor layer.

In this dissertation, …

Electron Drift-Mobility Measurements In Polycrystalline Cuin1-Xgaxse2 Solar Cells, Steluta A. Dinca, Eric A. Schiff, William N. Shafarman, Brian Egaas, Rommel Noufi, David L. Young

Physics - All Scholarship

We report photocarrier time-of-flight measurements of electron drift mobilities for the p-type CuIn_1-xGa_xSe₂ films incorporated in solar cells. The electron mobilities range from 0.02 to 0.05 cm^2/Vs and are weakly temperature-dependent from 100–300 K. These values are lower than the range of electron Hall mobilities (2-1100 cm²/Vs) reported for n-type polycrystalline thin films and single crystals. We propose that the electron drift mobilities are properties of disorder-induced mobility edges and discuss how this disorder could increase cell efficiencies.

Fundamental Properties Of Functional Zinc Oxide Nanowires Obtained By Electrochemical Method And Their Device Applications, Athavan Nadarajah

Dissertations and Theses

We report on the fundamental properties and device applications of semiconductor nanoparticles. ZnO nanowires and CdSe quantum dots were used, prepared, characterized, and assembled into novel light-emitting diodes and solar cells. ZnO nanowire films were grown electrochemically using aqueous soluble chloride-based electrolytes as precursors at temperatures below 90° C. Dopants were added to the electrolyte in the form of chloride compounds, which are AlCl₃, CoCl₂, CuCl₂, and MnCl₂. The optical, magnetic, and structural properties of undoped and transition-metal-ion doped ZnO nanowires were explored. Our results indicate that the as-grown nanowire structures have …

Thermodynamic Limit To Photonic-Plasmonic Light-Trapping In Thin Films On Metals, Eric A. Schiff

Physics - All Scholarship

We calculate the maximum optical absorptance enhancements in thin semiconductor films on metals due to structures that diffuse light and couple it to surface plasmon polaritons. The calculations can be used to estimate plasmonic effects on light-trapping in solar cells. The calculations are based on the statistical distribution of energy in the electromagnetic modes of the structure, which include surface plasmon polariton modes at the metal interface as well as the trapped waveguide modes in the film. The enhancement has the form 4n²+nλ/h (n – film refractive index, λ – optical wavelength, h …

Scanning Capacitance Spectroscopy On N+-P Asymmetrical Junctions In Multicrystalline Si Solar Cells, Chun-Sheng Jiang, Jennifer T. Heath, Helio R. Moutinho, Mowafak M. Al-Jassim

Faculty Publications

We report on a scanning capacitance spectroscopy (SCS) study on the n⁺-p junction of multicrystalline silicon solar cells. We found that the spectra taken at space intervals of ∼10 nm exhibit characteristic features that depend strongly on the location relative to the junction. The capacitance-voltage spectra exhibit a local minimum capacitance value at the electrical junction, which allows the junction to be identified with ∼10-nm resolution. The spectra also show complicated transitions from the junction to the n-region with two local capacitance minima on the capacitance-voltage curves; similar spectra to that have not been previously reported in …

Design Of Organic Tandem Solar Cells Using Pcpdtbt: Pc61 Bm And P3ht: Pc71bm, Gon Namkoong, Patrick Boland, Keejoo Lee, James Dean

Electrical & Computer Engineering Faculty Publications

We conducted optical and electrical simulations with the goal of determining the optimal design for conjugated polymer-fullerene tandem solar cells using poly[2,6-(4,4-bis-(2-ethylhexyl)- 4H-cyclopenta[2,1- b;3,4- b′] dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT): [6,6]-phenyl C₆₁ butyric acid methyl ester (PC₆₁ BM) as a bottom cell and poly(3-hexylthiophene) (P3HT): [6,6]-phenyl C₇₁ butyric acid methyl ester (PC₇₁BM) as a top cell. The effects of photon density, absorption, balanced and unbalanced charge carrier transport, and bimolecular recombination in the two subcells were incorporated into the simulations. We found that the maximum energy conversion efficiency (η) is 9% when charge carrier mobilities in …

Evolution Of The Band Structure Of Β-In2 S3−3x O3x Buffer Layer With Its Oxygen Content, N. Barreau, S. Marsillac, J. C. Bernède, L. Assmann

Electrical & Computer Engineering Faculty Publications

The evolution of the band structure of β-In2 S3−3x O3x (BISO) thin films grown by physical vapor deposition, with composition x, is investigated using x-ray photoelectron spectroscopy. It is shown that the energy difference between the valence-band level and the Fermi level remains nearly constant as the optical band gap of the films increases. As a consequence, the difference between the conduction band level and the Fermi level increases as much as the optical band gap of the films. The calculation of the electronic affinity [ ] of the BISO thin films shows that it decreases linearly from 4.65 …

Effect Of Ga Content On Defect States In Cuin1-XGaXSe2 Photovoltaic Devices, Jennifer T. Heath, J. David Cohen, William N. Shafarman, Dongxiang Liao, Angus Rockett

Faculty Publications

Defects in the band gap of CuIn_1-xGa_xSe₂ have been characterized using transient photocapacitance spectroscopy. The measured spectra clearly show response from a band of defects centered around 0.8 eV from the valence band edge as well as an exponential distribution of band tail states. Despite Ga contents ranging from Ga/(In+Ga)=0.0 to 0.8, the defect bandwidth and its position relative to the valence band remain constant. This defect band may act as an important recombination center, contributing to the decrease in device efficiency with increasing Ga content.

High-Efficiency Solar Cells Based On Cu(Inal)Se[Sub 2] Thin Films, S. Marsillac, P. D. Paulson, M. W. Haimbodi, R. W. Birkmire, W. N. Shafarman

Electrical & Computer Engineering Faculty Publications

A Cu(InAl)Se₂solar cell with 16.9% efficiency is demonstrated using a Cu(InAl)Se₂thin film deposited by four-source elemental evaporation and a device structure of glass/Mo/Cu(InAl)Se₂/CdS/ZnO/indium tin oxide/(Ni/Algrid)/MgF₂. A key to high efficiency is improved adhesion between the Cu(InAl)Se₂ and the Mo back contact layer, provided by a 5-nm-thick Ga interlayer, which enabled the Cu(InAl)Se₂ to be deposited at a 530 °C substrate temperature. Film and device properties are compared to Cu(InGa)Se₂ with the same band gap of 1.16 eV. The solar cells have similar behavior, with performance limited by recombination through …

Low‐Cost Technique For Preparing N‐Sb2S3/P‐Si Heterojunction Solar Cells, O. Savadogo, K. C. Mandal

Faculty Publications

No abstract provided.