Semiconductor and Optical Materials Commons^™

Cathode Buffer Layer For Improving Photovoltaic Performance Of Planar P-I-N Perovskite Solar Cells, Xiao-Dong Liu, Yong-Fang Li

Journal of Electrochemistry

Organic/inorganic hybrid metal halide perovskite semiconductor materials have drawn great attention for the application in solar cells in recent years because of their combined superior photoelectrical properties of inorganic semiconductors (with high dielectric constant and high charge carriers mobility) and organic semiconductors (with good solution processability and high absorbance). The power conversion efficiency (PCE) of the organometal halide perovskite solar cells (pero-SCs) based on CH₃NH₃PbI₃ has been increased dramatically in a few years from 3.8% to a certified 22.1%, primarily owing to the development of new interfacial materials, careful optimization of morphology, and perovskite crystallization …

Special Issue: Photoelectrochemistry And New Types Of Solar Cells, Chang-Jian Lin, Yong-Fang Li

Journal of Electrochemistry

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Prospects Of D-Π-A Structured Porphyrins And Their Photoelectrochemical Application, Shuang-Shuang Liu, Jian-Feng Lu, Ming-Kui Wang

Journal of Electrochemistry

Porphyrins and their metalloderivatives are a class of compounds exhibiting a wide variety of interesting and highly useful properties, such as chlorophyll. Porphyrins are particularly interesting in photoelectrochemical applications due to their structural similarity to chlorophylls in natural photosynthetic systems, as well as their strong and tunable absorption properties. Recently, various porphyrins have been extensively studied for their applications in solar cells, photocatalytic hydrogen production, optical information storage and others. This review will focus on the unique physical and chemical properties of D-π-A structured porphyrins, and their photovoltaic performances in dye-sensitized solar cells. A brief discussion in the future development …

Synthesis Of Acceptors For Use In Donor-Acceptor Copolymers And Characterization Of These Polymers, William D. Walker

Honors Theses

In this thesis, a selenium-derivatized acceptor was synthesized to examine the heavy atom effects of selenium on the position of the frontier molecular orbitals (HOMO/LUMO band gap) as opposed to sulfur in a donor-acceptor copolymer for use in light harvesting and detection applications. Over the course of this research, standard operating protocols for ultraviolet-visible (UV-Vis-NIR) and Fourier transform infrared (FT-IR) spectroscopies, as well as cyclic voltammetry (CV) characterization techniques were established. Once synthesized, the polymers were characterized through use of the established characterization protocols. The selenium-derivatized polymer exhibited a bathochromic shift compared to the sulfur analogue, with a solid-state absorption …

Direct Band Gap Gallium Antimonide Phosphide (Gasbxp1-X) For Solar Fuels., Harry Benjamin Russell

Electronic Theses and Dissertations

Photoelectrochemical water splitting has been identified as a promising route for achieving sustainable energy future. However, semiconductor materials with the appropriate optical, electrical and electrochemical properties have yet to be discovered. In search of an appropriate semiconductor to fill this gap, GaSbP, a semiconductor never tested for PEC performance is proposed here and investigated. Density functional theory (DFT+U) techniques were utilized to predict band gap and band edge energetics for GaSbP alloys with low amount of antimony. The overall objective of this dissertation is to understand the suitability of GaSb_xP_1-x alloys for photoelectrochemical water splitting application. Specifically, …

Strain Effects On The Work Function Of An Organic Semiconductor, Yanfei Wu, Annabel R. Chew, Geoffrey A. Rojas, Gjergji Sini, Greg Haugstad, Alex Belianinov, Sergei V. Kalinin, Hong Li, Chad Risko, Jean-Luc Brédas, Alberto Salleo, C. Daniel Frisbie

Chemistry Faculty Publications

Establishing fundamental relationships between strain and work function (WF) in organic semiconductors is important not only for understanding electrical properties of organic thin films, which are subject to both intrinsic and extrinsic strains, but also for developing flexible electronic devices. Here we investigate tensile and compressive strain effects on the WF of rubrene single crystals. Mechanical strain induced by thermal expansion mismatch between the substrate and rubrene is quantified by X-ray diffraction. The corresponding WF change is measured by scanning Kelvin probe microscopy. The WF of rubrene increases (decreases) significantly with in-plane tensile (compressive) strain, which agrees qualitatively with density …

The Dawn Of New Quantum Dots: Synthesis And Characterization Of Ge1-Xsnx Nanocrystals For Tunable Bandgaps., Richard J. Esteves

Theses and Dissertations

Ge_1-xSn_x alloys are among a small class of benign semiconductors with composition tunable bandgaps in the near-infrared spectrum. As the amount of Sn is increased the band energy decreases and a transition from indirect to direct band structure occurs. Hence, they are prime candidates for fabrication of Si-compatible electronic and photonic devices, field effect transistors, and novel charge storage device applications. Success has been achieved with the growth of Ge_1-xSn_x thin film alloys with Sn compositions up to 34%. However, the synthesis of nanocrystalline alloys has proven difficult due to larger discrepancies (~14%) in …

Uv Light-Induced Aggregation Of Titania Submicron Particles, Can Zhou, Yashar Bashirzadeh, Timothy A. Bernadowsky Jr., Xiaoyu Zhang

Mechanical & Aerospace Engineering Faculty Publications

In this study, aggregation of TiO₂ (rutile and anatase) submicron particles in deionized (DI) water under ultra-violet (UV) light irradiation was investigated. While no aggregation was observed in the dark, rutile and anatase submicron particles started aggregating upon application of UV light and ceased aggregation in about 2 and 8.4 h, respectively. It has been demonstrated that UV light directly mitigated the particle mobility of TiO₂, resulting in a neutralization effect of the Zeta potential. It was also observed that rutile particles aggregated much faster than anatase particles under UV radiation, indicating that the Zeta potential of …

Biolabeling Through The Use Of Water-Soluble Colloidal Quantum Dots, Cody Stombaugh

Honors Projects

Nanomaterials continues to be a growing field of study due to their wide range of potential applications. Quantum dots are artificially synthesized crystalline clusters of atoms able to confine electron motion as a result of their incredibly small size. Recently, medical applications of nanomaterials have expanded greatly. Quantum dots are ideal for biolabeling due to their rather narrow photoluminescence emission peaks. By synthesizing quantum dots of a specific diameter, it is possible to predetermine the peak photoluminescence wavelength of a sample. Through ligand exchange and immunoconjugation of the quantum dots with proteins, it is possible to use the quantum dots …

Molecular Helices As Electron Acceptors In High-Performance Bulk Heterojunction Solar Cells, Yu Zhong, M. Tuan Trinh, Rongsheng Chen, Geoffrey E. Purdum, Petr P. Khlyabich, Melda Sezen, Seokjoon Oh, Haiming Zhu, Brandon Fowler, Boyuan Zhang, Wei Wang, Chang-Yong Nam, Matthew Y. Sfeir, Charles T. Black, Michael L. Steigerwald, Yueh-Lin Loo, Fay Ng, X.-Y. Zhu, Colin Nuckolls

Publications and Research

Despite numerous organic semiconducting materials synthesized for organic photovoltaics in the past decade, fullerenes are widely used as electron acceptors in highly efficient bulk-heterojunction solar cells. None of the non-fullerene bulk heterojunction solar cells have achieved efficiencies as high as fullerene-based solar cells. Design principles for fullerene-free acceptors remain unclear in the field. Here we report examples of helical molecular semiconductors as electron acceptors that are on par with fullerene derivatives in efficient solar cells. We achieved an 8.3% power conversion efficiency in a solar cell, which is a record high for non-fullerene bulk heterojunctions. Femtosecond transient absorption spectroscopy revealed …

Morphology-Property Relationship For Binary Organic Thin Films, Alyssa Lynn Griffin

Master's Theses

Organic thin films can be readily mass-produced through solution-based fabrication methods including ink-printing and solution-casting because their light weight, flexibility, and inexpensive sources. Their applications range from organic field-effect transistors (OFET), organic solar cells (OSC), to organic light emitting diodes (OLEDs). Compared with pure component films, binary organic thin films (BOTF) allows for novel characteristics and specialized features to handle more demanding tasks. Due to the complex intermolecular interactions in BOTF, various microscopic phases with different morphological and electronic properties may be formed and this information is difficult to extract through conventional bulk measurements.

Organic thin films can be readily …

Effect Of Surfactant Architecture On Conformational Transitions Of Conjugated Polyelectrolytes, Greg A. Braggin

Master's Theses

Water soluble conjugated polyelectrolytes (CPEs), which fall under the category of conductive polymers, possess numerous advantages over other conductive materials for the fabrication of electronic devices. Namely, the processing of water soluble conjugated polyelectrolytes into thin film electronic devices is much less costly as compared to the processing of inorganic materials. Moreover, the handling of conjugated polyelectrolytes can be performed in a much more environmentally friendly manner than in the processing of other conjugated polymers because conjugated polyelectrolytes are water soluble, whereas other polymers will only dissolve in toxic organic solvents. The processing of electronic devices containing inorganic constituents such …

Investigation Of The Dynamics Of Photocarriers During Photoelectrochemical Water Splitting By Combination Of Photoelectrochemistry And Transient Absorption Spectroscopy, Wen-Hua Leng

Journal of Electrochemistry

Semiconductor photoelectrochemical hydrogen production is an important and promising technology for utilizing solar energy. The efficiency of hydrogen production depends on the efficiencies of separation and transport of photo-generated carriers. A deep understanding of the behavior of these processes has guiding significance for designing efficient solar hydrogen device. photoelectrochemical and transient absorption spectroscopy methods are powerful tool for studying the microscopic dynamics and mechanism of photocatalytic reaction. This review describes the part of the latest results of the author regarding the semiconductor photoelectrochemical hydrogen production obtained by these methods,and the problems and future research priorities in this field are proposed.

Effects Of Conformational Transformations On Electronic Transport Properties Of Optical Molecular Switches: An Ab Initio Study, Yuan-Yuan He, Jian-Wei Zhao

Journal of Electrochemistry

A series of model molecules with 4 kinds of conformational transformations have been investigated as optical molecular switches by using density functional theory combined with nonequilibrium Green’s function method. The theoretical calculations show that molecules after conformational transformations have photoswitching characteristics. We find that the photochromic molecules with the same conformational transformation usually have a similar current on/off state when they are applied as photoshwitches. Among these transformations, the molecular switch with E(“trans”)/Z(“cis”)-isomerisation of the NN double bond has the highest current on-off ratio. The influences of the energy gap (HLG) between the highest occupied molecular orbital (HOMO) and the …

Monodentate, Bidentate And Photocrosslinkable Thiol Ligands For Improving Aqueous Biocompatible Quantum Dots, Hiroko Takeuchi

Graduate Theses and Dissertations

Water-soluble Quantum Dots (QDs) are highly sensitive fluorescent probes that are often used to study biological species. One of the most common ways to render QDs water-soluble for such applications is to apply hydrophilic thiolated ligands to the QD surface. However, these ligands are labile and can be easily exchanged on the QD surface, which can severely limit their application. As one way to overcome this limitation while maintaining a small colloidal size of QDs, we developed a method to stabilize hydrophilic thiolated ligands on the surface of QDs through the formation of a crosslinked shell using a photocrosslinking approach. …

Fe, Co And Ni Adatoms Adsorbed On Silicene: A Dft Study, Kent Gang '14, Siva Gangavarapu '14, Matthew Deng '14, Glenn W. "Max" Mcgee, Ron Hurlbut, Michael Lee Dao Kang, Sean Ng Peng Nam, Harman Johll, Tok Eng Soon

Student Publications & Research

Two-dimensional materials have attracted much research attention given their intriguing properties. The latest member of this class of materials is silicene. In this work, we investigate the adsorption of Fe, Co and Ni adatoms on silicene using plane-wave density functional theory calculations within the Perdew-Burke-Ernzerhof parameterization of the generalized gradient approximation for the exchange-correlation potential. In particular, we calculate the binding energy, magnetization, and projected electronic configurations of these adatoms adsorbed at different sites on the silicene. Our calculations show that the hole site (i.e. in the centre of a hexagonal-like arrangement of Si atoms) is the most stable configuration …

Strategic Electronic Property Control Of Self-Assembling Pyrazine-Acenes, Lacie Brownell

UNLV Theses, Dissertations, Professional Papers, and Capstones

Control of electronic properties in organic semiconductor materials is essential for electro-optical applications such as field-effect transistors, light-emitting diodes, and photovoltaic devices. This work is focused on two systems that highlight different approaches for the manipulation of electronic properties: (I) the development of electron-deficient (n-type) materials by selective lowering of E_LUMO and (II) low energy gap materials by controlling both E_LUMO and E_HOMO

To specifically lower E_LUMO, a pyrazine-acene π-platform was extended using electron-withdrawing moieties. These include: pyridine, pyrazine, and benzothiadiazole (system I). From the base pyrazine-acene, the most significant change in E_LUMO of …

Sodium Carbonate Catalyzed Photoelectrochemical Water Splitting Over Tio2 Nanotubes Photoanode, De-Sheng Kong, Jing Wang, Xue-Di Zhang, Xi Zhao, Chao Wang, Yuan-Yuan Feng, Wen-Juan Li

Journal of Electrochemistry

Surface recombination of the photogenerated electron-hole pairs at semiconductor/electrolyte interface is one of the most essential reasons responsible for lowering photoconversion efficiency (Φ) of light to chemical energy for photoelectrochemical (PEC) water splitting reaction. In this paper, the catalytic effect of sodium carbonate on the oxygen evolution reaction (OER) over TiO₂ nanotubes photoanode during PEC water splitting was investigated by performing photocurrent and ac impedance measurements. It was demonstrated that the addiction of 1 mmol•L^-1 Na₂CO₃ in 0.5 mol•L^-1 NaClO₄ electrolyte can effectively improve the charge transfer properties for the photogenerated holes across …

Kinetic Study Of Photoelectrochemical Oxidation Of Lignin Model Compounds On Tio2 Nanotubes, Min Tian, Daniel Liba, Aicheng Chen

Journal of Electrochemistry

In this study, TiO₂ nanotubes were prepared via the electrochemical oxidation of titanium substrates in a non-aqueous electrolyte and their morphology and microstructures were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The photoelectrochemical oxidation of two lignin model compounds, 1-(3,4-dimethoxyphenoxy)-2-(2-methoxyphenoxy)-1,3-propanediol (DMP) and 3-hydroxy-1-(3,4-dimethoxyphenoxy)-2-(2-methoxyphenoxy)-1,3-propanone (HDM), was investigated. A new band appeared at ~304 nm during the photoelectrochemical oxidation of DMP. The rate of DMP intermediate formation was amplified with the increase of initial concentrations, while it was diminished with increased temperature. Despite the similarity in structure between HDM and DMP, there are only small increases in absorbance …

Semiconductor Nanocrystals: From Quantum Dots To Quantum Disks, Zheng Li

Graduate Theses and Dissertations

The bottom-up colloidal synthesis opened up the possibility of finely tuning and tailoring the semiconductor nanocrystals. Numerous recipes were developed for the preparation of colloidal semiconductor nanocrystals, especially the traditional quantum dots. However, due to the lack of thorough understanding to those systems, the synthesis chemistry is still on the empirical level. CdS quantum dots synthesis in non-coordinating solvent were taken as a model system to investigate its molecular mechanism and formation process, ODE was identified as the reducing agent for the preparation of CdS nanocrystals, non-injection and low-temperature synthesis methods developed. In this model system, we not only proved …

Influence Of Tert-Butylpyridine On The Band Energetics Of Nanostructured Tio2 Electrodes And The Photoelectrochemical Properties Of Dye-Seneitized Electrodes, Shu-Ming Yang, Ji-Chao Wang, Hui-Zhi Kou, Hong-Bin Xue, Hong-Jun Wang, Yu-Ling Guo

Journal of Electrochemistry

The flat band edges (Efb) of nanostructured TiO₂ electrodes in electrolyte solutions with tert-butylpyridine (TBP) of different concentrations have been determined with spectroelectrochemical technique. TBP played a role in band energetics of nanostructured TiO₂ electrodes. The Efb values of -2.25, -2.46 and -2.62 V were determined in three 0.2 mol•L^-1 tetrabutylammonium perchlorate (TBAP) acetonitrile electrolytes which contain 0, 0.2 and 0.4 mol•L^-1 TBP respectively. The addition of Li+ ions shifted Efb positively. The Efb values of -1.12, -1.22 and -1.30 V were determined in three 0.2 mol•L^-1 LiClO₄ acetonitrile electrolytes which contain 0, 0.2 …

Chemical And Electronic Structure Of Surfaces And Interfaces In Compound Semiconductors, Sujitra Pookpanratana

UNLV Theses, Dissertations, Professional Papers, and Capstones

The interface formation between two different materials is important in applications for optoelectronic devices. Often, the success or performance of these devices is dependent on the formation of these heterojunctions. In this work, the surface and interfaces in such materials for optoelectronic devices are investigated by a suite of X-ray analytical techniques including X-ray photoelectron (XPS), X-ray excited Auger electron (XAES), and X-ray emission (XES) spectroscopies to provide novel insight.

For the group III-nitrides (e.g., AlxGa1-xN) used in many light emitting devices, a significant challenge exists to form an Ohmic contact. The electron affinities and band gaps of GaN and …

Photoelectrochemical Properties Of N, S, And Cl Modified Nano Tio2 Thin Films, Hong Yun, Chang-Jian Lin, Jing Li, Rong-Gui Du

Journal of Electrochemistry

The nitrogen(N),sulfur(S) and chlorine(Cl) modified nano TiO₂ thin films were prepared by adding Ti(O-n-Bu)₄ as the precursor into concentrated HNO₃,H₂SO₄ and HCl Solutions,respectively,on different substrates in a sol-gel process.The photoelectrochemical performances of N,S and Cl modified nano TiO₂ thin films have been studied by UV-vis(DRS),photocurrent curves,EIS and OCP-time curves.N-modified TiO₂ nano films show better surface structure,which helps to improve the quantum efficiency of nano TiO₂ thin films.

Synthesis And Characterization Of Zinc Oxide Nanostructures., Khalifa Said Zahran Al-Azri

Student Works (2010-2019)

The growth mechanism, morphology, structure and optical properties of the ZnO nanostructures grown on bare and gold-coated silicon substrates using carbothermal reaction at atmospheric pressure were investigated under different growth conditions. The ZnO nanostructures formed were studied as a function of substrate location, furnace temperature, Ar gas flow rate, deposition time and ZnO powder to carbon powder mass ratio. The morphology and structure of the samples were characterized using the fieldemission scanning electron microscopy (FESEM), energy dispersive x-ray spectroscopy(EDX) spectrum, x-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). It was found that in both silicon and gold-coated silicon …

The Thermoluminescence Properties Of Manganese Doped Zns Nanophosphor., Khalid Humaid Zahir Al-Hinai

Student Works (2010-2019)

The thermoluminescence (TL) properties of Manganese (Mn) doped ZnS nanophosphors were investigated after gamma irradiation at room temperature. The ZnS:Mn nanophosphors were prepared by chemical precipitation method by using Zinc sulfate, Sodium sulfide and Manganese sulfate. 1 mole, 2 moles and 3 moles of Manganese sulfate were used to have different concentrations of Mn in doped ZnS. The formation of the nanophosphors was characterized by high resolution scanning electron microscopy FESEM, XRD and EDX. The obtained products consist of particles with the dimension about 85–150nm. Comparison between ZnS nanophosphors and commercial ZnS powder glow curves was studied. It was observed …

Synthesis And Characterization Of Silicon Oxide And Silicon Carbide Nanostructures., Majid Salim Mohammed Al-Ruqieshi

Student Works (2010-2019)

Silicon oxide nanostructures have attracted extensive interests in recent years due to their physical and optical properties. SiOx nanostructures are synthesized by catalytic and non-catalytic approaches. With catalytic approach, long and uniform amorphous silicon oxide nanowires, nanofibers (comet and tree like), nanocakes and nanocages were synthesized on Si substrate by carbothermal evaporation reactions of TiO2 at high temperature. The SiOx nanowires were about 13 nm to 243 nm in diameters and 194 nm to several microns in length and the nanofibres with diameter between 8 nm to 30 nm and around 50 nm to 2.5μm in length. The diameter and …

Synthesis And Characterization Of A [Ru(Bpy)2(Ncs)2] Derivative For Use As A Dye-Sensitizer In Nanocrystalline Solar Cells, Joel Thomas Kirner

Honors Program Theses

After extensive review of the field of dye-sensitized solar cells, the molecule [Ru(4,4’- dicarboxy-2,2’-bipyridine)(4,4’-di-(2-(2-pyridyl)ethenyl)-2,2’-bipyridine)(NCS)2] has been designed as an original contribution to the field. This dye sensitizer was chosen by derivatizing upon the structure of the standard sensitizer, cis-diisothiocyanatobis(4,4’-dicarboxylic acid-2,2’- bipyridine)ruthenium(II) (N3), by extending the conjugation of one bipyridine ligand. This structural derivatization should enhance light harvesting by red-shifting the dye’s absorbance and increasing the dye’s molar absorptivity, which should result in a dye-sensitized solar cell with higher efficiency. The Density Functional Theory (DFT) molecular orbital calculations of the new dye complex indicate that the HOMO is highly localized …

Enhanced Visible Light Photoelectrochemical Performances With Nitrogen Doped Tio2 Nanowire Arrays, Xiao-Jun Lv, Yue-Ming Li, Hao Zhang, Da Chen, Jennifer Hensel, Jin Z Zhang, Jing-Hong Li

Journal of Electrochemistry

Self-organized anodic anatase TiO₂ nanowire arrays doped with nitrogen have been successfully fabri-cated and their photoelectrochemical(PEC) properties have been characterized and found to be substantially im-proved compared to undoped nanowires or commercial P25 nanoparticles.Photocurrent measured with monochro-matic incident light showed that the incident photon-to-current efficiency(IPCE,%) values of nanowire arrayelectrodes with or without N-doping were obviously higher than that of commercial P25 nanoparticle electrodes,and nitrogen-doped TiO₂ nanowire arrays(NTNA) had noticeable absorption in the visible region.The NTNAelectrodes showed the highest photocurrent density and power conversion efficiency under 100 mW/cm² visiblelight illumination.A maximumolphotoconversion efficiency of 0.52% was achieved for the …

Photoelectrochemical Properties Of Tio2 Nanoparticles, Jie Qu, Ying Li, Qi-Wei Jiang, Xue-Ping Gao

Journal of Electrochemistry

The protonated titanate nanoparticles were obtained at room temperature and subsequently calcined at different temperatures(300 ℃,400 ℃,500 ℃,600 ℃ and 700 ℃) in air.The obtained products were characterized by XRD,TEM and UV-Vis.It is found that the grain sizes of TiO₂ nanoparticles calcined at 300 ℃ were about 20 nm,and increased gradually with the temperature rise.Photoelectric performance was measured with I～V curve and electrochemical impedance spectroscopy(EIS).The TiO₂ nanoparticles obtained at 500 ℃ showed the best photoelectrochemical properties with a photovoltaic conversion efficiency of 6.39%,which is much higher than those at other temperatures.In addition,it is also demonstrated that the charge …

Study On The Texturization Of C-Si Wafers By Different Kinds Of Alkaline For Heterojunction Solar Cells, Yu-Hua Dou, Yu-Qin Zhou, Mei-Fang Zhu, Shuang Song, Feng-Zhen Liu, Jin-Long Liu, Zhan-Jun Zhang

Journal of Electrochemistry

The texturization of(100) crystalline silicon(c-Si) wafer was studied by field-emission scanning electron microscope using different kinds of etchant: sodium hydroxide,sodium carbonate and tribasic sodium phosphate.By optimizing the etching parameters,the lowest values of averaged reflectance(Rav) were obtained to be 9.70% for NaOH,9.76% for Na₂CO₃ and 8.63% for Na₃PO₄·12H₂O,which is comparable to that of the wafer with textured surface covered with an anti-reflection coating of either silicon nitride or thermally grown silicon dioxide.The relation of Rav and surface morphology of textured wafer was analyzed.Moreover,special emphasis was put on the role of isopropyl alcohol(IPA) …