Download or read book Spectroscopic Ellipsometry Studies of Thin Film Si H Materials in Photovoltaic Applications from Infrared to Ultraviolet written by Laxmi Karki Gautam and published by . This book was released on 2016 with total page 192 pages. Available in PDF, EPUB and Kindle. Book excerpt: Optimization of thin film photovoltaics (PV) relies on the capability for characterizing the optoelectronic and structural properties of each layer in the device over large areas and correlating these properties with device performance. This work builds heavily upon that done previously by us, our collaborators, and other researchers. It provides the next step in data analyses, particularly that involving study of films in device configurations maintaining the utmost sensitivity within those same device structures. In this Dissertation, the component layers of thin film hydrogenated silicon (Si:H) solar cells on rigid substrate materials have been studied by real time spectroscopic ellipsometry (RTSE) and ex situ spectroscopic ellipsometry (SE). Growth evolution diagrams has been used to guide deposition of materials with good optoelectronic properties in the actual hydrogenated amorphous silicon (a-Si:H) PV device configuration. The nucleation and evolution of crystallites forming from the amorphous phase were studied using near infrared to ultraviolet spectroscopic ellipsometry in situ, during growth for films prepared as a function of hydrogen to reactive gas flow ratio R = [H2] /{[SiH4] + [Si2H6]. Furthermore, the major challenge in Si:H manufacturing is that quantitative analysis, characterization, and control of the relative nanocrystalline and amorphous volume fractions within mixed-phase films were covered during these studies. In conjunction with higher photon energy measurements, the presence and relative absorption strength of silicon-hydrogen infrared modes were measured by infrared extended ellipsometry measurements to gain some insight into chemical bonding. Structural and optical models have been developed for the back reflector (BR) structure consisting of sputtered undoped zinc oxide (ZnO) on top of silver (Ag) coated glass substrates. Characterization of the free-carrier absorption properties in Ag and the interface formed when Ag is over-coated with ZnO were also studied by infrared extended spectroscopic ellipsometry. Measurements ranging from 0.04 to 5 eV were used to extract layer thicknesses, composition, and optical response in the form of complex dielectric function spectra (e = e1 + ie2) for undoped a-Si:H layers in a substrate n-i-p a-Si:H based PV device structure and on TCO coated glass for p-i-n configurations.

Download or read book Spectroscopic Ellipsometry for Photovoltaics written by Hiroyuki Fujiwara and published by Springer. This book was released on 2019-01-10 with total page 628 pages. Available in PDF, EPUB and Kindle. Book excerpt: Spectroscopic ellipsometry has been applied to a wide variety of material and device characterizations in solar cell research fields. In particular, device performance analyses using exact optical constants of component layers and direct analyses of complex solar cell structures are unique features of advanced ellipsometry methods. This second volume of Spectroscopic Ellipsometry for Photovoltaics presents various applications of the ellipsometry technique for device analyses, including optical/recombination loss analyses, real-time control and on-line monitoring of solar cell structures, and large-area structural mapping. Furthermore, this book describes the optical constants of 148 solar cell component layers, covering a broad range of materials from semiconductor light absorbers (inorganic, organic and hybrid perovskite semiconductors) to transparent conductive oxides and metals. The tabulated and completely parameterized optical constants described in this book are the most current resource that is vital for device simulations and solar cell structural analyses.

Download or read book Introduction to Spectroscopic Ellipsometry of Thin Film Materials written by Andrew T. S. Wee and published by John Wiley & Sons. This book was released on 2022-03-08 with total page 213 pages. Available in PDF, EPUB and Kindle. Book excerpt: A one-of-a-kind text offering an introduction to the use of spectroscopic ellipsometry for novel material characterization In Introduction to Spectroscopic Ellipsometry of Thin Film Materials: Instrumentation, Data Analysis and Applications, a team of eminent researchers delivers an incisive exploration of how the traditional experimental technique of spectroscopic ellipsometry is used to characterize the intrinsic properties of novel materials. The book focuses on the scientifically and technologically important two-dimensional transition metal dichalcogenides (2D-TMDs), magnetic oxides like manganite materials, and unconventional superconductors, including copper oxide systems. The distinguished authors discuss the characterization of properties, like electronic structures, interfacial properties, and the consequent quasiparticle dynamics in novel quantum materials. Along with illustrative and specific case studies on how spectroscopic ellipsometry is used to study the optical and quasiparticle properties of novel systems, the book includes: Thorough introductions to the basic principles of spectroscopic ellipsometry and strongly correlated systems, including copper oxides and manganites Comprehensive explorations of two-dimensional transition metal dichalcogenides Practical discussions of single layer graphene systems and nickelate systems In-depth examinations of potential future developments and applications of spectroscopic ellipsometry Perfect for master’s- and PhD-level students in physics and chemistry, Introduction to Spectroscopic Ellipsometry of Thin Film Materials will also earn a place in the libraries of those studying materials science seeking a one-stop reference for the applications of spectroscopic ellipsometry to novel developed materials.

Download or read book Spectroscopic Ellipsometry Studies of Thin Film A Si H nc Si H Micromorph Solar Cell Fabrication in the P i n Superstrate Configuration written by Zhiquan Huang and published by . This book was released on 2016 with total page 467 pages. Available in PDF, EPUB and Kindle. Book excerpt: Spectroscopic ellipsometry (SE) is a non-invasive optical probe that is capable of accurately and precisely measuring the structure of thin films, such as their thicknesses and void volume fractions, and in addition their optical properties, typically defined by the index of refraction and extinction coefficient spectra. Because multichannel detection systems integrated into SE instrumentation have been available for some time now, the data acquisition time possible for complete SE spectra has been reduced significantly. As a result, real time spectroscopic ellipsometry (RTSE) has become feasible for monitoring thin film nucleation and growth during the deposition of thin films as well as during their removal in processes of thin film etching. Also because of the reduced acquisition time, mapping SE is possible by mounting an SE instrument with a multichannel detector onto a mechanical translation stage. Such an SE system is capable of mapping the thin film structure and its optical properties over the substrate area, and thereby evaluating the spatial uniformity of the component layers. In thin film photovoltaics, such structural and optical property measurements mapped over the substrate area can be applied to guide device optimization by correlating small area device performance with the associated local properties. In this thesis, a detailed ex-situ SE study of hydrogenated amorphous silicon (a Si:H) thin films and solar cells prepared by plasma enhanced chemical vapor deposition (PECVD) has been presented. An SE analysis procedure with step-by-step error minimization has been applied to obtain accurate measures of the structural and optical properties of the component layers of the solar cells. Growth evolution diagrams were developed as functions of the deposition parameters in PECVD for both p-type and n-type layers to characterize the regimes of accumulated thickness over which a-Si:H, hydrogenated nanocrystalline silicon (nc-Si:H) and mixed phase (a+nc)-Si:H thin films are obtained. The underlying materials for these depositions were newly-deposited intrinsic a-Si:H layers on thermal oxide coated crystalline silicon wafers, designed to simulate specific device configurations. As a result, these growth evolution diagrams can be applied to both p-i-n and n-i-p solar cell optimization. In this thesis, the n-layer growth evolution diagram expressed in terms of hydrogen dilution ratio was applied in correlations with the performance of p-i-n single junction devices in order to optimize these devices. Moreover, ex-situ mapping SE was also employed over the area of multilayer structures in order to achieve better statistics for solar cell optimization by correlating structural parameters locally with small area solar cell performance parameters. In the study of (a-Si:H p-i-n)/(nc-Si:H p-i-n) tandem solar cells, RTSE was successfully applied to monitor the fabrication of the top cell, and efforts to optimize the nanocrystalline p-layer and i-layer of the bottom cell were initiated.

Download or read book Spectroscopic Ellipsometry as a Versatile Non contact Probe of Optical Electrical and Structural Properties in Thin Films written by Maxwell M. Junda and published by . This book was released on 2017 with total page 134 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation describes a collection of studies that demonstrate and expand the many configurations in which spectroscopic ellipsometry (SE) can be applied to material characterization, primarily for thin films. The materials investigated each have relevance to photovoltaics, but the methods described herein can be applicable to the study of materials used in virtually any application. In aggregate, the measurement and data modeling techniques represent a broad set of tools that can be used to study the optoelectronic and structural characteristics of amorphous, polycrystalline, nanostructured, or inhomogeneous layers within thin film solar cell devices. The capabilities for SE to determine properties of a sample of interest well beyond simple optical response functions are demonstrated. In particular, SE is used in a real-time, in situ configuration where a series of measurements are taken continually during the deposition of all layers in complete hydrogenated amorphous silicon (a-Si:H) solar cells. Thus, the application of real-time SE (RTSE) to the entire process of solar cell fabrication is realized. The optical response and thicknesses of each layer are obtained and are used to interpret variation in the measured electrical performance between different devices. The SE-derived results are then used as inputs to a simulation of the expected current generated by the devices, the results of which were successful in identifying damage to a transparent conducting layer resulting from exposure to plasma during sample fabrication as the source of performance losses. The study of full a-Si:H-based solar cells revealed the presence of subtle optical property gradients within individual layers. The ability to characterize slight inhomogeneity using RTSE was further developed using measurements collected for a-Si:H films deposited under various conditions and on various substrates. In particular, this work systematically examines a range of modeling configurations in the virtual interface analysis (VIA) technique used to extract the results. Through testing the influence of two specific modeling parameters on the overall error associated with each model, the optimum analysis models are identified, enabling the extraction of the most accurate results. Ultimately, the evolution of an optical broadening parameter is extracted for aSi:H films grown on various substrates and under various conditions. Limitations of the VIA technique are also identified and discussed. Next, the effects of varying deposition and processing conditions on the optical response of resultant films is studied through ex situ SE measurements of a series of oxygenated cadmium sulfide (CdS:O) films. A custom parametric description of the optical response of these films applicable to polycrystalline semiconductors is developed that makes use of physically realistic descriptions of the optical features over the full measured spectral range. From the resulting optical properties, increasing oxygen presence during deposition is shown to suppress absorption in the films and modify the band gap energy for as-deposited films. Additionally, annealing is shown to revert all CdS:O band gap energies to that of pure cadmium sulfide (2.4 eV) and improve crystallographic order. Since CdS:O is used in high performance thin film photovoltaics, these optical results contribute to an explanation of what the role of this material is specifically in improved device performance, specifically the decreased optical absorption at ultraviolet photon energies. Finally, the benefits of extending SE into the THz frequency regime is investigated. Since THz SE is an emerging subfield of ellipsometry unique THz-specific considerations are investigated and discussed. Limitations imposed by the instrument are identified and efforts to identify the minimum measurement resolution and range that will still produce acceptable results are presented as a means for decreasing total measurement time. Then, the results of THz SE applied to single bulk crystals is presented where sensitivity to carrier concentrations as low as 1014 cm-3 is demonstrated. Finally, a study of the effects of doping on a single walled carbon nanotube (SWCNT) thin film is reported. More specifically, the optical response of the SWCNT film over a wide spectral range spanning the THz to the ultraviolet and uniaxially anisotropic electrical properties are determined for the film in two doping states.

Download or read book Spectroscopic Ellipsometry for Photovoltaics written by Hiroyuki Fujiwara and published by Springer. This book was released on 2019-01-10 with total page 602 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides a basic understanding of spectroscopic ellipsometry, with a focus on characterization methods of a broad range of solar cell materials/devices, from traditional solar cell materials (Si, CuInGaSe2, and CdTe) to more advanced emerging materials (Cu2ZnSnSe4, organics, and hybrid perovskites), fulfilling a critical need in the photovoltaic community. The book describes optical constants of a variety of semiconductor light absorbers, transparent conductive oxides and metals that are vital for the interpretation of solar cell characteristics and device simulations. It is divided into four parts: fundamental principles of ellipsometry; characterization of solar cell materials/structures; ellipsometry applications including optical simulations of solar cell devices and online monitoring of film processing; and the optical constants of solar cell component layers.

Download or read book Spectroscopic Ellipsometry Studies of CdS CdTe Thin Films and Photovoltaic Devices written by Michelle Nicole Sestak and published by . This book was released on 2012 with total page 217 pages. Available in PDF, EPUB and Kindle. Book excerpt: As the demand for clean, renewable energy sources increases, the development of high efficiency, low cost photovoltaic devices from thin films becomes increasingly important. Spectroscopic ellipsometry is a promising tool for the characterization and investigation of thin film photovoltaic devices and the component materials from which they are made. This tool can be applied either in-situ and in real-time using high speed multichannel instruments, or ex-situ using slower wavelength-by-wavelength scanning instruments. Spectroscopic ellipsometry is promising for use in thin film photovoltaics because it provides the thicknesses of the individual layers and their optical properties, which in turn provide insights into the light collection required for photocurrent generation. Advanced forms of ellipsometry include (i) ex-situ mapping spectroscopic ellipsometry with a multichannel ellipsometer, which provides information on thickness and optical property non-uniformities over large areas of a coated substrate, and (ii) real-time spectroscopic ellipsometry with similar high speed instrumentation, which provides information on thin film nucleation, coalescence, and growth, as well as changes in the structure of the material over time. Both advanced forms of ellipsometry have been applied in this Dissertation to analyze thin films with applications in photovoltaics. In this Dissertation research, ex-situ mapping ellipsometry has been used to study Au nanoparticle thin films. These films are useful because they can be integrated into solar cells to promote light trapping within the absorber layers, and hence, increase the overall efficiency of the cells. Studying these films with mapping spectroscopic ellipsometry provides a means for determining thickness uniformity over large areas of the sample for scale-up of the deposition processes. The uniformity of other parameters of the Au nanoparticle films such as the plasmon resonance band energy and its broadening are also critical, as these can be optimized to ensure maximum coupling of light into the solar cell absorber layer. In addition, the advanced methods of real-time spectroscopic ellipsometry (RTSE) have been used to characterize a series of CdTe thin films deposited via magnetron sputtering. In this case, analysis of RTSE data provides information on the nucleation, coalescence, and growth of thin films under different deposition conditions. The time evolution of the thicknesses of the nucleating, bulk-like, and surface roughness layers provide an indication of the growth mode, and enable the distinction of initial clustering from initial layer-by-layer growth. The growth mode shows consistent trends with the deposition parameters. In addition, RTSE provides accurate complex dielectric functions of the growing films, since the films are free from oxidation, and surface roughness can be taken into account in the analysis. From the dielectric functions, information on the void fraction, electron mean free path, and stress in these films can be obtained. Also presented in this Dissertation are the results of a study of CdTe solar cells deposited by magnetron sputtering at varying argon pressures and for varying CdCl2 treatment times. These cells were studied through analyses of the current-voltage (J-V) curves and through comparisons of J-V deduced parameters for cells of varying pressures and treatment times. In two independent series of depositions, it was surprising that samples deposited at a specific argon pressure (10 mTorr) performed the best. This optimum pressure separates a regime at low pressures in which the sputtered species experience no collisions upon transit to the substrate, and a regime at high pressures in which the sputtered species experience multiple collisions and are nearly thermalized. Also obtained in this research were quantum efficiency curves for the best performing cells. The measured quantum efficiency for a 10 mTorr sample could be simulated using parameters obtained from ex-situ spectroscopic ellipsometry measurements. Assumptions made in this simulation identified the nature of current losses in the solar cells. Finally, this Dissertation presents a study of a new flexible CdTe solar cell configuration fabricated via an advanced substrate transfer process. In this process, the solar cell is deposited on a temporary superstrate of aluminum foil and transferred to a permanent polymer substrate. This process is used since flexible polymers cannot withstand the deposition temperatures used for the fabrication of CdTe solar cells via the industrial processes of vapor transport deposition and close space sublimation. This novel process has been shown previously to be useful for production of a-Si:H solar modules, and this Dissertation research showed for the first time that it may also be useful for CdTe solar cells, even though the process requires further optimization to reach commercializable efficiencies.

Download or read book Multichannel Spectroscopic Ellipsometry for CdTe Photovoltaics written by Prakash Koirala and published by . This book was released on 2015 with total page 363 pages. Available in PDF, EPUB and Kindle. Book excerpt: Spectroscopic ellipsometry (SE) in the mid-infrared to ultraviolet range has been implemented in order to develop and evaluate optimization procedures for CdTe solar cells at the different stages of fabrication. In this dissertation research, real time SE (RT-SE) has been applied during the fabrication of the as-deposited CdS/CdTe solar cell. Two areas of background research were addressed before undertaking the challenging RT-SE analysis procedures. First, optical functions were parameterized versus temperature for the glass substrate and its overlayers, including three different SnO2 layers. This database has applications not only for RT-SE analysis but also for on-line monitoring of the coated glass itself at elevated temperature. Second, post-deposition modifications of substrate have been studied by infrared spectroscopic ellipsometry (IR-SE) prior to the RT-SE analysis in order to evaluate the need for such modification in the analysis. With support from these background studies, RT-SE has been implemented in analyses of the evolution of the thin film structural properties during sputter deposition of polycrystalline CdS/CdTe solar cells on the transparent conducting oxide (TCO) coated glass substrates. The real time optical spectra collected during CdS/CdTe deposition were analyzed using the optical property database for all substrate components as a function of measurement temperature. RT-SE enables characterization of the filling process of the surface roughness modulations on the top-most SnO2 substrate layer, commonly referred to as the high resistivity transparent (HRT) layer. In this filling process, the optical properties of this surface layer are modified in accordance with an effective medium theory. In addition to providing information on interface formation to the substrate during film growth, RT-SE also provides information on the bulk layer CdS growth, its surface roughness evolution, as well as overlying CdTe interface formation and bulk layer growth. Information from RT-SE at a single point during solar cell stack deposition assists in the development of a model that has been used for mapping the properties of the completed cell stack, which can then be correlated with device performance. Independent non-uniformities in the layers over the full area of the cell stack enable optimization of cell performance combinatorially.The polycrystalline CdS/CdTe thin-film solar cell in the superstrate configuration has been studied by SE using glass side illumination whereby the single reflection from the glass/film-stack interface is collected whereas that from the ambient/glass interface and those from multiple glass/film-stack reflections are rejected. The SE data analysis applies an optical model consisting of a multilayer stack with bulk and interface layers. The dielectric functions ¿¿for the solar cell component materials were obtained by variable-angle and in-situ SE. Variability in the properties of the materials are introduced through free parameters in analytical expressions for the dielectric functions. In the SE analysis of the complete cell, a step-wise procedure ranks all free parameters of the model, including thicknesses and those defining the spectra in¿¿, according to their ability to reduce the root-mean-square deviation between simulated and measured SE spectra. The results for the best fit thicknesses compare well with electron microscopy. From the optical model, including all best-fit parameters, the solar cell quantum efficiency (QE) can be simulated without free parameters, and comparisons with QE measurements have enabled the identification of losses. The capabilities have wide applications in off-line photovoltaic module mapping and in-line monitoring of coated glass at intermediate stages of production. Mapping spectroscopic ellipsometry (M-SE) has been applied in this dissertation research as an optimization procedure for polycrystalline CdS/CdTe solar cell fabrication on TCO coated glass superstrates. During fabrication of these solar cells, the structure undergoes key processing steps after the sputter-deposition of the CdS/CdTe. These steps include CdCl2 treatment of the CdTe layer and subsequent deposition of ultrathin Cu. Additional steps involve final metal back contact layer deposition and an anneal for Cu diffusion that completes the device. In this study, we have fabricated cells with variable absorber thicknesses, ranging from 0.5 to 2.5 ¿m, and variable CdCl2 treatment times, ranging from 5 to 30 min. Because both CdS window and Cu back contact layers are critical for determining device performance, the ability to characterize their deposition processes and determine the resulting process-property-performance relationships is important for device optimization. We have applied M-SE to map the effective thickness (volume/area) of the CdS and Cu films over 15 cm x 15 cm substrates prior to the fabrication of 16 x 16 arrays of dot cells. We report correlations of cell performance parameters with the CdCl2 treatment time and with the effective thicknesses from M-SE analysis. We demonstrate that correlations between optical/structural parameters extracted from M-SE analysis and device performance parameters facilitate process optimization. We have explored and applied p-type semiconducting materials as novel back contact materials in CdTe solar cells. Wide band-gap, p-type doped, hydrogenated amorphous silicon-carbon alloy (a-Si1-xCx:H:B) layers deposited by plasma enhanced chemical vapor deposition (PECVD) under conditions that yield efficient hydrogenated amorphous silicon (a Si:H) p-i-n solar cells have been applied as back contacts to sputter-deposited CdTe superstrate solar cells. We report a maximum observed Voc value of 0.78 V and a best initial efficiency of ~ 7.7 % (relative to an ~ 12% standard cell baseline) without the introduction of Cu into the back contact region. Instability of solar cells that incorporate such back contacts have hindered their further development. We also applied copper indium diselenide (CuInSe2) as a novel back contact material in CdTe solar cells in the superstrate configuration. We report a maximum observed Voc value of 0.68 V and a best efficiency of ~ 6.4 % (relative to an ~ 12.6 % standard cell baseline) without the introduction of Cu.

Download or read book Real Time Spectroscopic Ellipsometry Studies of Thin Film Materials and Structures for Photovoltaic Applications written by Jian Li and published by . This book was released on 2010 with total page 227 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Spectroscopic Ellipsometry written by Harland G. Tompkins and published by Momentum Press. This book was released on 2015-12-16 with total page 138 pages. Available in PDF, EPUB and Kindle. Book excerpt: Ellipsometry is an experimental technique for determining the thickness and optical properties of thin films. It is ideally suited for films ranging in thickness from sub-nanometer to several microns. Spectroscopic measurements have greatly expanded the capabilities of this technique and introduced its use into all areas where thin films are found: semiconductor devices, flat panel and mobile displays, optical coating stacks, biological and medical coatings, protective layers, and more. While several scholarly books exist on the topic, this book provides a good introduction to the basic theory of the technique and its common applications. The target audience is not the ellipsometry scholar, but process engineers and students of materials science who are experts in their own fields and wish to use ellipsometry to measure thin film properties without becoming an expert in ellipsometry itself.

Download or read book Spectroscopic Ellipsometry Studies of Ag and ZnO Thin Films and Their Interfaces for Thin Film Photovoltaics written by Deepak Sainju and published by . This book was released on 2015 with total page 388 pages. Available in PDF, EPUB and Kindle. Book excerpt: Many modern optical and electronic devices, including photovoltaic devices, consist of multilayered thin film structures. Spectroscopic ellipsometry (SE) is a critically important characterization technique for such multilayers. SE can be applied to measure key parameters related to the structural, optical, and electrical properties of the components of multilayers with high accuracy and precision. One of the key advantages of this non-destructive technique is its capability of monitoring the growth dynamics of thin films in-situ and in real time with monolayer level precision. In this dissertation, the techniques of SE have been applied to study the component layer materials and structures used as back-reflectors and as the transparent contact layers in thin film photovoltaic technologies, including hydrogenated silicon (Si:H), copper indium-gallium diselenide (CIGS), and cadmium telluride (CdTe). The component layer materials, including silver and both intrinsic and doped zinc oxide, are fabricated on crystalline silicon and glass substrates using magnetron sputtering techniques. These thin films are measured in-situ and in real time as well as ex-situ by spectroscopic ellipsometry in order to extract parameters related to the structural properties, such as bulk layer thickness and surface roughness layer thickness and their time evolution, the latter information specific to real time measurements. The index of refraction and extinction coefficient or complex dielectric function of a single unknown layer can also be obtained from the measurement versus photon energy. Applying analytical expressions for these optical properties versus photon energy, parameters that describe electronic transport, such as electrical resistivity and electron scattering time, can be extracted. The SE technique is also performed as the sample is heated in order to derive the effects of annealing on the optical properties and derived electrical transport parameters, as well as the intrinsic temperature dependence of these properties and parameters. One of the major achievements of this dissertation research is the characterization of the thickness and optical properties of the interface layer formed between the silver and zinc oxide layers in a back-reflector structure used in thin film photovoltaics. An understanding of the impact of these thin film material properties on solar cell device performance has been complemented by applying reflectance and transmittance spectroscopy as well as simulations of cell performance.

Download or read book Application of Spectroscopic Ellipsometry written by Kiran Ghimire and published by . This book was released on 2017 with total page 105 pages. Available in PDF, EPUB and Kindle. Book excerpt: Spectroscopic ellipsometry (SE) is an important optical characterization technique, applicable to a wide variety of samples such as a single substrate material to a multilayer complex structured opto-electronic device. SE is always known to be an accurate and precise measurement of structural, optical, and electrical properties of material especially for a multilayer stack, including photovoltaic devices. This presentation demonstrates examples ranging from a gadolinium gallium garnet (Gd3Ga5O12) single crystal to environmentally unstable polycrystalline organo-halide perovskite thin films to perovskite based solar cells. A significant component of this work is real time monitoring of time sensitive perovskite thin film during the growth as well as post deposition degradation and demonstrated illustrative ideas of data analysis techniques for real time measurement. A commercially available single crystal Gd3Ga5O12 is taken as the first case. The structural and optical properties of Gd3Ga5O12 from infrared to ultraviolet (0.034 to 5.89 eV) was extracted. A simple ellipsometry model is applied to analyze the data from near infrared to ultraviolet (0.74 to 5.89 eV). Additional transmission measurement adds to the accuracy below the band gap region where the absorption coefficient is less than 1000 cm-1 and subsequently helps to detect sub band gap features near 3.95 to 5.06 eV. The band gap is identified in the ultraviolet (UV), while transverse and longitudinal optical phonon modes in the infrared (IR) region are detected. Analysis of IR spectra and quantifying these phonon modes was challenging because of nine absorption peaks present and a sufficiently large number of (>30) fitting parameters. Another case study of this research work is on (FASnI3)1-x(MAPbI3)x (x = 0.00, 0.20, 0.35, 0.40, 0.60, and 1.00) perovskite thin films formed by combining formamidinium tin iodide (FASnI3) and methylammonium lead iodide (MAPbI3). Those perovskite films are time sensitive i.e. degrades in open atmosphere (moisture, oxygen, light). In order to avoid the degradation during the measurement, all the measurements are performed with least possible minimum exposure (~2 mins) with laboratory ambient. A similar ellispometric model as used in Gd3Ga5O12 was applied. The major finding is the variations in the absorption band edge and higher energy critical point transitions as functions of relative MAPbI3 and FASnI3 contents. The real time monitoring of perovskite thin films is a key results of this work, particularly real time monitoring of MAPbI3 thin film during the deposition and post deposition degradation. These studies enable detection of phase instabilities and changes in composition and structure occurring either during growth as a function of different deposition conditions or after deposition as a function of external stimuli (moisture, oxygen, and light) causing perovskite decomposition or phase changes. An illustrative example of analysis model for real time monitoring is demonstrated. From the real time analysis, the presence of phase segregated and unreacted component materials at the substrate/film and film/ ambient interfaces are identified. The time dependent effective perovskite film, unreacted components, and phase segregated layers thicknesses during the measurements are tracked. Finally, external quantum efficiency (EQE) simulations of perovskite based solar cells have been reported. The simulated EQE compare fairly well with their experimental values. Overall, the research work presented in this dissertation gives an insight into ellipsometry analysis techniques as well as numerous opportunities to improve and optimize the perovskite based solar cell towards an ideal most efficient perovskite in solar cell devices.

Download or read book Spectroscopic Ellipsometry Studies of II VI Semiconductor Materials and Solar Cells written by Jie Chen and published by . This book was released on 2010 with total page 229 pages. Available in PDF, EPUB and Kindle. Book excerpt: The multilayer optical structure of thin film polycrystalline II-VI solar cells such as CdTe is of interest because it provides insights into the quantum efficiency as well as the optical losses that limit the short-circuit current. The optical structure may also correlate with preparation conditions, and such correlations may assist in process optimization. A powerful probe of optical structure is real time spectroscopic ellipsometry (SE) that can be performed during the deposition of each layer of the solar cell. In the CdCl2 post-deposition treatment process used for thin film polycrystalline II-VI solar cells, the optical properties of each layer of the cell change during the process due to annealing as well as to the elevated temperature. In this case, ex-situ SE before and after treatment becomes a reasonable option to determine the optical structure of CdCl2-treated CdTe thin film solar cells. CdTe solar cells pose considerable challenges for analysis by ex-situ SE. First, the relatively large thickness of the as-deposited CdTe layer leads to considerable surface roughness, and the CdCl2 post-deposition treatment generates significant additional oxidation and surface inhomogeneity. Thus, ex-situ SE measurements in reflection from the free CdTe surface before and after treatment can be very difficult. Second, SE from the glass side of the cell is adversely affected by the top glass surface which generates a reflection that is incoherent with respect to the reflected beams from the thin film interfaces and consequently depolarization if collected along with these other beams. In this research, the first problem is solved through the use of a succession of Br2+methanol treatments that smoothens the CdTe free surface, and the second problem is solved through the use of a 60° prism optically-contacted to the top glass surface that eliminates the top surface reflection. In addition, the succession of a Br2+methanol treatment not only smoothens the CdTe surface but also enables CdTe etching in a layer-by-layer fashion. In this way, it has been possible to track the optical properties of the CdTe component layer as a function of depth from the surface toward the CdS/CdTe interface in order to gain a better understanding of the film structure. In this study, ex-situ spectroscopic ellipsometry was applied first to investigate the optical properties of the TEC-15 glass substrate, and then to extract the optical properties of thin film CdTe and CdS both as-deposited and CdCl2-treated. After obtaining all the optical properties of the solar cell component layer materials, a comprehensive ex-situ SE analysis has been applied to extract the optical structure of a single thin film of CdCl2-treated CdTe, and finally to obtain the optical structure of the CdCl2 post-deposition treated CdTe solar cell. Based on the fundamental studies in this thesis, various aspects of the solar cell structure after the complicated CdCl2 treatment have been determined. In future work the role of the key parameters of CdCl2 post-deposition treatment process will be explored including: the temperature and treatment time. As a result, a correlation will be established between solar cell performance and film structure. Finally, an understanding of how solar cell structure can be optimized to achieve the highest solar cell performance may be possible through improved control of the CdCl2 post-treatment process.

Download or read book Spectroscopic Ellipsometry for Photovoltaics written by Hiroyuki Fujiwara and published by . This book was released on 2018 with total page 616 pages. Available in PDF, EPUB and Kindle. Book excerpt: Spectroscopic ellipsometry has been applied to a wide variety of material and device characterizations in solar cell research fields. In particular, device performance analyses using exact optical constants of component layers and direct analyses of complex solar cell structures are unique features of advanced ellipsometry methods. This second volume of Spectroscopic Ellipsometry for Photovoltaics presents various applications of the ellipsometry technique for device analyses, including optical/recombination loss analyses, real-time control and on-line monitoring of solar cell structures, and large-area structural mapping. Furthermore, this book describes the optical constants of 148 solar cell component layers, covering a broad range of materials from semiconductor light absorbers (inorganic, organic and hybrid perovskite semiconductors) to transparent conductive oxides and metals. The tabulated and completely parameterized optical constants described in this book are the most current resource that is vital for device simulations and solar cell structural analyses.

Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1992 with total page 1556 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Science and Technology of Thin Films written by F. C. Matacotta and published by World Scientific. This book was released on 1995 with total page 369 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book brings together detailed discussions by leading experts on the various innovative aspects of thin films growth, deposition and characterization techniques, and new thin film materials and devices. It addresses through the different viewpoints of the contributors, the major problem of thin films science - the relation between the energy of the condensing species and the resulting properties of the films. Some of the issues considered include energetic condensation, bombardment stabilization, pulsed electron beam ablation, orientation and self-organization of organic, ferroelectric and nanoparticle thin films. Several chapters focus on applications such as the recent developments in organic optoelectronics, large area electronic technology and superconducting thin film devices.

Download or read book Applications of Multichannel Spectroscopic Ellipsometry for CdTe Photovoltaics written by Xinxuan Tan and published by . This book was released on 2017 with total page 286 pages. Available in PDF, EPUB and Kindle. Book excerpt: Spectroscopic ellipsometry (SE) is a powerful tool for non-destructive evaluation of thin films consisting of single layers or multilayers on substrates. For such thin films, SE can provide structural parameters and component material optical properties over a wide spectral range. Further analyses of these optical properties can provide additional information of interest on the physical and chemical properties of the materials. Installation of the SE instrument on a deposition chamber enables monitoring of the thin film during deposition. This experiment, referred to as in-situ real time SE (RTSE), enables high surface sensitivity, fast data acquisition, and non-invasive probing which lead to unique insights into the dynamics of film growth. In this dissertation research, RTSE was applied for analysis of the structural evolution of oxygenated CdS (CdS:O) films deposited on c-Si substrates using different [O2 ]/{[Ar] + [O2]} gas flow ratios. The analysis of RTSE data provides valuable information including the initial film growth mode (e.g. layer-by-layer or clustering), subsequent bulk layer and surface roughness thickness evolution, the growth rate in terms of effective thickness (or volume/area), and the final film optical properties. As an additional application of SE, ex situ through-the-glass mapping SE (TG-M-SE) has been used to study the structural properties and area uniformity of CdS/CdTe solar cells over large areas. The mapping results can be correlated with the efficiency of solar cells fabricated over the same area, exploiting inevitable non-uniformities in the process to identify the optimum structural parameters for highest efficiency solar cells. In a second component of this research, RTSE has proven to be very powerful for the development and optimization of thin film FeS2 deposited by a novel hybrid sputtering/co-evaporation method. This effort started with the sputtering of elemental Fe metal thin films and proceeded to the evaporation of sulfur simultaneously with Fe deposition using different overall rates and substrate temperatures. The effects of these deposition parameters on the resulting iron sulfide film properties were explored. The nucleation, growth evolution, and optical properties of thin film FeS2 deposited by this hybrid method are key outcomes of this study that relies on in-situ RTSE. Other characterization techniques including X-ray diffractometry, scanning electron microscopy SEM, and energy-dispersive X-ray spectroscopy (EDS) were used in the dissertation research to determine the crystal structure, surface microstructure, and the S:Fe atomic ratio of the iron sulfide films to complement the RTSE analysis. In the final component of this dissertation research, CdTe/CdS solar cells in the substrate configuration were fabricated and studied. Development of CdTe/CdS solar cells in this non-standard configuration provides an alternative approach for exploring CdTe back contacts that may require high-temperature vacuum processing. The experimental research on this subject started with a study of the effect of CdS bath temperature on the CdS/CdTe solar cell performance in the superstrate configuration in an attempt to advance the process for use in the substrate configuration. Materials including MoO3, copper indium selenide (CIS), and nitrogen doped CIS (CIS:N) were studied as p-type back contact interlayers between Mo and CdTe in the CdTe/CdS substrate configuration solar cells. The performance of the solar cells incorporating these p-type back contacts are compared and discussed in the dissertation.