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Measurement of the quantum efficiency of TMAE and TEA from threshold to 120 nm

Description: Several existing and planned high energy physics experiments incorporate detectors which use either TMAE (tetrakis-dimethylaminoethylene) or TEA (triethylamine) as their photosensitive agent. Understanding the operation of these devices requires knowledge of the absolute photoionization quantum efficiencies and absorption lengths of TMAE and TEA. In an experiment performed at the National Synchrotron Light source at Brookhaven National Laboratory, we have measured these parameters from 120 nm to 280 nm. The quantum efficiencies were normalized to the known photoionization yields of benzene and cis-2-butene. The results of these measurements and details of the experiment are presented in this paper.
Date: January 1, 1986
Creator: Holroyd, R. A.; Preses, J. M.; Woody, C. L. & Johnson, R. A.
Partner: UNT Libraries Government Documents Department

Plasma-assisted CVD of fluorinated, hydrogenated amorphous silicon. Final technical report, September 15, 1979-September 15, 1980

Description: During the past year, approximately 300 large-area (400 cm/sup 2/) PIN hydrogenated amorphous silicon (a-Si:H) solar cells were fabricated and tested. a-Si:H PIN cells which were plasma deposited at 200/sup 0/ to 350/sup 0/ were found to have high internal currents (13mA/cm/sup 2/), whereas those which were deposited by CVD at 500/sup 0/ to 650/sup 0/C had low internal currents. When corrected for optical losses in the top electrode, the internal quantum efficiency vs wavelength for the PIN cells indicated a peak value above 80% at about 525nm, which decreased monotonically to zero at about 725 nm. When the published values of RCA and EXXON were corrected similarly for optical loss, nearly identical values of internal quantum efficiencies were found. Calculations based on a model proposed by Cody et al of EXXON indicated that the depletion width was less than 0.4 microns for all PIN cells, thereby limiting junction efficiency in the red portion of the solar spectrum since the 1/e photon range exceeds this value. A novel inverted NIP cell was tested and found to have its maximum quantum response shifted to 625 nm. Also, an amorphous boron (a-B) layer deposited on a-Si:H to form a PIN heterojunction improved blue response and Voc. A combination of the red-responsive cells and the a-B heterojunction cells could raise efficiency to 8%.
Date: January 1, 1980
Creator: Coleman, J. H.; Hammes, J. P. & Wiesmann, H. J.
Partner: UNT Libraries Government Documents Department


Description: We report a new approach to the generation of high-current, high-brightness electron beams. Primary electrons are produced by a photocathode (or other means) and are accelerated to a few thousand electron-volts, then strike a specially prepared diamond window. The large Secondary Electron Yield (SEY) provides a multiplication of the number of electrons by about two orders of magnitude. The secondary electrons drift through the diamond under an electric field and emerge into the accelerating proper of the ''gun'' through a Negative Electron Affinity surface of the diamond. The advantages of the new approach include the following: (1) Reduction of the number of primary electrons by the large SEY, i.e. a very low laser power in a photocathode producing the primaries. (2) Low thermal emittance due to the NEA surface and the rapid thermalization of the electrons. (3) Protection of the cathode from possible contamination from the gun, allowing the use of large quantum efficiency but sensitive cathodes. (4) Protection of the gun from possible contamination by the cathode, allowing the use of superconducting gun cavities. (5) Production of high average currents, up to ampere class. (6) Encapsulated design, making the ''load-lock'' systems unnecessary. This paper presents the criteria that need to be taken into account in designing the amplifier.
Date: June 21, 2004
Partner: UNT Libraries Government Documents Department


Description: We present the results of our investigation of bulk lead, along with various types of lead films, as suitable photocathode materials for superconducting RF injectors. The quantum efficiency of each sample is presented as a function of the photon energy of the incident light, from 3.9 eV to 6.5 eV. Quantum efficiencies of 0.5% have been obtained. Production of a niobium cavity with a lead-plated cathode is underway.
Date: May 16, 2005
Partner: UNT Libraries Government Documents Department

Efficiency of Scintillator Materials in the Energy Range 8.0-32.0 keV

Description: X-ray microtomography requires the measurement of x-ray attenuation along ray paths through a specimen, and on the inversion of these data to obtain a spatially resolved mapping of the microstructure of the specimen. To do this efficiently, two-dimensional array detectors are often used to measure the transmitted x-rays by capturing and recording each x-ray incident on the detector. The highest resolution CT instruments perform this by converting the incident x-rays to visible light, and then focusing this light onto a charge-coupled-device (CCD) detector. The light output of the scintillator (photons per incident x-ray), the numerical aperture of the optical lens system, and the quantum efficiency of the CCD govern the efficiency of the detection process. Several years earlier, our group performed an investigation aimed at determining the best scintillator material for high-resolution synchrotron CT. The selection criteria included light output in the 8-32 keV energy range, the spatial resolution of the scintillator, the wavelength of the scintillation radiation, and the stability and ease of polishing of the scintillator. A list of the scintillators that we considered, with the exceptions of the more recently developed glass scintillators, is provided in Table 1. Among these scintillators, we concluded that single crystal cadmium tungstate was optimum; we have used this material in all subsequent synchrotron CT systems. Since this original study, several doped-glass scintillators have become available. The LSO (Lu orthosilicates) scintillators, developed for PET scanning, show considerable light output at high energy (energies above 500 keV). Theoretically, the light output of these scintillators should be twice that of the cadmium tungstate. The purpose of this study was to determine the efficiency of two such scintillators (LSO:Yt and IQI-401 high density terbium activated glass) in the energy range from 8-32 keV.
Date: July 1, 2002
Creator: Kinney, J H & Haupt, D L
Partner: UNT Libraries Government Documents Department


Description: In this paper we present a study of the photoemission properties of lead at several UV wavelengths, including a study of the damage threshold of electroplated lead under laser cleaning. A quantum efficiency in excess of 0.1% has been achieved for a laser cleaned, electroplated lead sample with a laser wavelength of 193 nm. Niobium cathodes have been measured for comparison, and lead is found to be a superior photoemitter for all measured wavelengths.
Date: July 5, 2004
Partner: UNT Libraries Government Documents Department

Target Diagnostic Technology Research and Development for the LLNL ICF and HED Programs

Description: The National Ignition Facility (NIF) is under construction at LLNL for the Department of Energy Stockpile Stewardship Program. It will be used for experiments for Inertial Confinement Fusion (ICF) Ignition, High Energy Density (HED) science, and basic science. Many issues confront experimentalists who wish to design, fabricate, and install diagnostics on the NIF. To foster this process the ICF and HED programs at LLNL have formed a diagnostic research and development group to look at issues outside the charter of facility diagnostics (core diagnostics). We will present data from instrumentation and associated technology that is being developed by this group. A major portion of our instrumentation work is on improvements for readout systems. We have several efforts related to CCD device development. Work has been done in collaboration with the University of Arizona to backthin a large format CCD device (36mm{sup 2}). This work has shown good results. The device has very high quantum efficiency, low noise readout and high charge transfer efficiency. The device is being fielded in direct optical, direct x-ray and 13-15 RV electron readout applications. In addition to readout device development we have completed work on a CCD readout system. With a commercial vendor we have developed a large format, compact, Ethernet addressable CCD camera system. This system fits in shoebox size volume, is thermal electrically cooled, supports a variety of CCD devices and can be run from remote locations via TCP/IP protocol. We are also doing work to improve streak camera systems. We have coupled our large format CCD system to an MK2 Kentech streak tube. Improvements have been made to the resolution and dynamic range of the system. Similar improvements have been made to the LLNL optical streak camera systems. We will present data from the optical and x-ray streak camera work. In addition ...
Date: August 22, 2003
Creator: Bell, P; Bennett, C; Holder, J; Kimbrough, J; Landen, O; Lerche, D et al.
Partner: UNT Libraries Government Documents Department

Optimization of Phase-Engineered a-Si:H-Based Multi-Junction Solar Cells: Second Annual Technical Status Report, January 2003--January 2004

Description: This subcontract report entails investigation of engineering improvements in the performance and stability of solar cells in a systematic way. It consists of the following four tasks: Task 1-Materials research and device development; Task 2-Process improvement directed by real-time diagnostics; Task 3-Device loss mechanisms; and Task 4-Characterization strategies for advanced materials. The real-time spectroscopic ellipsometry (RTSE) multichamber is near completion, and trial depositions with a-Si:H will begin shortly. Construction of the new dual beam photoconductivity (DBP) apparatus has been completed, and the new capabilities are being used in studies on a-Si:H thin films. A new apparatus is being constructed for in-depth studies on the mechanisms limiting the performance of a-Si:H solar cells and the two track studies (cells and films) of the Staebler-Wronski Effect. The capabilities include the ability to integrate the cell characteristics including the quantum efficiency, at different temperatures on both p-i-n and n-i-p solar cells.
Date: August 1, 2004
Creator: Wronski, C. R.; Collins, R. W.; Vlahos, V.; Pearce, J. M.; Deng, J.; Albert, M. et al.
Partner: UNT Libraries Government Documents Department

Process R&D for CIS-Based Thin-Film PV: Annual Technical Report, January 2003--January 2004

Description: This subcontract report describes Shell Solar Industries' outstanding progress in the initial commercialization of high-performance thin-film CIS technology. Cumulative production for 2002 exceeded 1 MW-about twice the production rate for 2001. SSI 2003 capacity was about 3 MW per year, whereas production for 2003 was just over 1.2 MW per year. Introducing the new product accounts for the main difference between production and capacity. Average laminate efficiency for 2003 was 11.0% with a full width of only 11% of the average. This distribution is nominally the same as the distribution for 2002, but with an about 33% increase in production volume. Line yield increased from about 60% in 2000 to about 85% in 2002. Maintenance of this high line yield was demonstrated during 2003. Process R&D during this and previous subcontract periods, both at SSI and in collaboration with NREL teams, has demonstrated the potential for further cost performance improvements: minimization of transients, increased efficiency, and improved packaging. Long-term outdoor stability has been demonstrated at NREL where {approx}30 x 30 cm and {approx} 30 x 120 cm modules with multiple prototype package designs have undergone testing for over 14 years. Field failure mechanisms related to particular package designs and errors during production have been clearly identified. Additional circuit plate or packaging process variables may have affected durability during particular production timeframes; when losses have been observed, the losses correlated with date of deployment or prototype module configuration. Prototype glass/glass packages for individual 40-W circuit plates have passed accelerated tests, including the damp-heat test. This package incorporates an edge seal developed in collaboration with the National Thin-Film PV Module Reliability Team. Developing and testing of 40-W glass/glass packages is being extended to a new 80-W product made using two nominally 40-W circuit plates laminated to a common front sheet.
Date: October 1, 2004
Creator: Tarrant, D. E. & R., Gay R.
Partner: UNT Libraries Government Documents Department

Synthesis and Optical Properties of Photochromic Perinaphthothioindigo

Description: (1,2-naphtho)(1,8-naphtho)thioindigo (PNT) has been synthesized following a simple Friedel-Crafts route and its photochemical properties in toluene and PMMA characterized. PNT is a photochromic molecule capable of reversible photoisomerization between a yellow form (cis-PNT, {lambda}{sub max} = 484 nm) and a purple form (trans-PNT, {lambda}{sub max} = 595 nm). The stable purple form converts to the yellow form with a trans-PNT to cis-PNT conversion quantum yield of 0.027 in toluene and 0.062 in PMMA. The unstable yellow form exhibits a cis-PNT to trans-PNT quantum efficiency of conversion of 0.27-0.85 in toluene and 0.17-0.68 PMMA, with highest conversion efficiency occurring in the vicinity of its {lambda}{sub max} of 484 nm. Trans-PNT has a strong fluorescence quantum yield, 0.14 (toluene) and 0.16 (PMMA). For samples prepared photochemically in the cis-PNT form, slow thermal relaxation to the trans form occurs in the dark, with a half life of about 17 hours in toluene (25 C) and even slower, 168 hours, in PMMA. The property of photoswitching between fluorescent and non-fluorescent forms makes this material a candidate for many applications in imaging and data storage. An anomalous excitation profile for the fluorescence from trans-PNT, showing a dip at {approx}600 nm, is an agreement with the wavelength-dependent quantum yield of conversion from trans-PNT to cis-PNT, which is highest at the absorbance peak.
Date: February 10, 2005
Creator: Cherepy, N J & Sanner, R D
Partner: UNT Libraries Government Documents Department

Analysis of Depletion-Region Collection in GaInNAs Solar Cells

Description: We provide qualitative insight into depletion-region collection in GaInNAs cells to (1) understand the effect of diffusion length L on the QE; and (2) describe the magnitude of L required to get adequate current from the cell. We use Wolf's equations for the QE including a drift field E, and model E as being equal to the junction built-in voltage distributed uniformly across the depletion region. This allows us to calculate the QE as a function of L and depletion width WD. We show that if L is sufficiently small, increasing WD can actually decrease the QE. To determine how long L needs to be in a practical GaInNAs junction, we calculate from the QE the short-circuit current density as a function of WD and L. This allows us to estimate that Lambipolar needs to be greater than roughly 1 {micro}m in order to obtain enough photocurrent for the 4-junction application, giving guidance to the experimental effort to develop such cells.
Date: February 1, 2005
Creator: Friedman, D. J.; Ptak, A. J.; Kurtz, S. R. & Geisz, J. F.
Partner: UNT Libraries Government Documents Department

Time dependant quantum efficiency and dark current measurements in an RF photocathode injector with a high quantum efficiency cathode

Description: Studies of photo-emission and field emission behavior in an RF gun have been carried out. Unexpected phenomena were observed. In situ changes in the cathode's quantum efficiency and dark current with time were seen during operation of the photo-injector. These changes were correlated with the magnetostatic field at the cathode. In addition, multipacting has been observed under certain conditions. Recent measurements indicate a correlation between multipacting and anomalous photo- and field emission behavior.
Date: May 1, 2005
Creator: Fliller, R. P., III; Edwards, H.; /Fermilab; Hartung, W. & /Michigan State U., NSCL
Partner: UNT Libraries Government Documents Department

Float-Zone and Czochralski Crystal Growth and Diagnostic Solar Cell Evaluation of a New Solar-Grade Feedstock Source: Preprint

Description: This conference paper describes the Czochralski (CZ) and float-zone (FZ) crystals were grown from experimental solar-grade silicon (SOG-Si) feedstock materials developed by Crystal Systems. The materials were metallurgical-grade Si and highly boron-doped p-type electronic-grade Si (EG-Si) reject material, both of which were gaseous melt-treated to remove boron. Crystal growth observations, lifetime and impurity characterization of the grown crystals, and device performance of wafers from them are presented. Devices made directly on treated high-B EG-Si feedstock have a little over half the efficiency of devices made from control CZ samples. However, devices on CZ and FZ crystals grown from the treated high-B EG-Si feedstock have comparable PV performance (14.0% and 13.8% efficiency, respectively) to that of CZ control samples (14.1%).
Date: May 1, 2002
Creator: Ciszek, T. F.; Page, M. R.; Wang, T. H. & Casey, J. A.
Partner: UNT Libraries Government Documents Department

Hybrid Nanorod-Polymer Solar Cell: Final Report; 19 July 1999--19 September 2002

Description: With the support of this grant, we successfully demonstrated that semiconductor nanorods can be used to fabricate readily processed and efficient hybrid solar cells together with polymers. By controlling nanorod length, we changed the distance over which electrons are transported directly through the thin-film device. Tuning the bandgap by altering the nanorod radius enabled us to optimize the overlap between the absorption spectrum of the cell and the solar emission spectrum. A photovoltaic device consisting of 7-nm by 60-nm CdSe nanorods and the conjugated polymer poly-3(hexylthiophene) was assembled from solution with an external quantum efficiency of over 54% and a monochromatic power conversion efficiency of 6.9% under 0.1 mW/cm2 illumination at 515 nm. Under AM 1.5 Global solar conditions, we obtained a power conversion efficiency of 1.7%.
Date: August 1, 2003
Creator: Alivisatos, A. P.
Partner: UNT Libraries Government Documents Department

Productivity Enhancement for Manufacturing of Amorphous Silicon PV Modules: Final Technical Report, 1 July 2002--30 June 2003

Description: During Phase I, EPV conducted parallel research efforts for achieving higher stabilized module power output through improvements in several manufacturing processing steps, with particular emphasis on the thin-film deposition process. The dual goals of achieving a 10% gain in stabilized output and a 20% reduction in direct costs were accomplished. Early in Phase I, a thorough evaluation of single-junction and tandem amorphous silicon (a-Si) modules was carried out with the goal of determining the best option to use (as a function of application) based on EPV's proprietary batch deposition process. The analysis considered total energy delivery over realistic conditions and the impact on equipment needs and production costs. EPV has concluded that the tandem process is more appropriate for its needs at this time. The overall objective of this subcontract over its two-year duration is to continue the advancement of EPV's a-Si production manufacturing technology and improve the product ion equipment used in manufacturing. This will allow EPV to reduce module costs by increasing module output, throughput, and yield.
Date: November 1, 2003
Creator: Volltrauer, H.
Partner: UNT Libraries Government Documents Department

Nondestructive Performance Characterization Techniques for Module Reliability

Description: This paper describes nondestructive characterization techniques for module reliability. These techniques include light and dark current versus voltage and related analysis such as resistance, diode quality factor, and dark current. The use of the NREL laser scanner at zero volts and forward bias is also described as a technique to uncover cracks, shunts, and open-circuit regions in a module. Quantum-efficiency measurements of isolated cells or regions in a module are also possible. The interpretation of laser-scanning data is enhanced by hot-spot testing with an infrared camera or thermographic paper. Specialized nondestructive techniques have also been developed to determine the shunt resistance of individual cells in a module by selective shading of cells under sunlight. Ultraviolet fluorescence and reflectivity measurements at NREL have proven useful in evaluating encapsulant stability.
Date: May 1, 2003
Creator: Emery, K.
Partner: UNT Libraries Government Documents Department

Advanced CIGS Photovoltaic Technology: Annual Technical Report, 15 November 2001-14 November 2002

Description: Energy Photovoltaics, Inc. (EPV) has consistently pursued a vacuum-based approach to CIGS production, using novel linear-source technology and standard soda-lime glass substrates. It has also chosen to develop processing methods with worker safety in mind. These choices result in layers having controllable purity and low physical defects, and production without significant hazards. Considerations such as these are important in helping to minimize the processing costs of CIGS. Technically, thin-film PV technologies have advanced considerably in the last few years. EPV successfully produced high-quality 0.43m2 Mo-coated glass substrates that, when cut, enabled NREL to produce 17.1% CIGS cells on such substrates. EPV successfully used novel linear evaporative sources for supply of Cu, In, Ga, and Se to form CIGS on 0.43m2 substrates, producing modules with Voc's of up to 37 V. A new approach to buffer-layer deposition was pioneered through synthesis of the compound ZnIn2Se4 and its use as a source material. In addition, the current generated in exploratory a-Si/a-Si/CIGS stacked devices was increased from 6 to 13 mA/cm2. Supporting these programs, EPV's upgraded analytical laboratories provided rapid in-house feedback concerning material and device properties. The objective of this subcontract is to develop and assemble the various pieces of new technology that EPV considers essential for cost-effective production of CIGS modules. The long-term objective of the Thin Film PV Partnership Program is to demonstrate low-cost, reproducible modules of 15% aperture-area efficiency.
Date: May 1, 2003
Creator: Delahoy, A. E. & Chen, L.
Partner: UNT Libraries Government Documents Department

1-MeV-Electron Irradiation of GaInAsN Cells: Preprint

Description: This conference paper describes the GaInAsN cells that are measured to retain 933% and 894% of their original efficiency after exposure to 5 X 1014 and 1 X 1015 cm-2 1-MeV electrons, respectively. The rate of degradation is not correlated with the performance at beginning of life (BOL). The depletion width remains essentially unchanged, increasing by< 1%. Temperature-coefficient data for GaInAsN cells are also presented. These numbers are used to project the efficiency of GaInAsN-containing multijunction cells. The GaInAsN junction is not currently predicted to increase the efficiencies of the multijunction cells. Nevertheless, GaInAsN-containing multijunction cell efficiencies are predicted to be comparable to those of the conventional structures, and even small improvements in the GaInAsN cell may lead to higher multijunction cell efficiencies, especially for high-radiation applications and when cell operating temperature is low.
Date: May 1, 2002
Creator: Kurtz, Sarah; King, R. R.; Edmondson, K. M.; Friedman, D. J. & Karam, N. H.
Partner: UNT Libraries Government Documents Department

Large-area PSPMT based gamma-ray imager with edge reclamation

Description: We describe a coded aperture, gamma-ray imager which uses a CsI(Na) scintillator coupled to an Hamamatsu R3292 position-sensitive photomultiplier tube (PSPMT) as the position-sensitive detector. We have modified the normal resistor divider readout of the PSPMT to allow use of nearly the full 10 cm diameter active area of the PSPMT with a single scintillator crystal one centimeter thick. This is a significant performance improvement over that obtained with the standard readout technique where the linearity and position resolution start to degrade at radii as small as 3.5 cm with a crystal 0.75 crn thick. This represents a recovery of over 60% of the PSPMT active area. The performance increase allows the construction of an imager with a field of view 20 resolution elements in diameter with useful quantum efficiency from 60-700 keV. In this paper we describe the readout technique, its implementation in a coded aperture imager and the performance of that imager.
Date: September 21, 2000
Creator: Ziock, K-P & Nakae, L
Partner: UNT Libraries Government Documents Department

Degradation Analysis of Weathered Crystalline-Silicon PV Modules: Preprint

Description: We present an analysis of the results of a solar weathering program that found a linear relationship between maximum power degradation and the total UV exposure dose for four different types of commercial crystalline Si modules. The average degradation rate for the four modules types was 0.71% per year. The analysis showed that losses of short-circuit current were responsible for the maximum power degradation. Judging by the appearance of the undegraded control modules, it is very doubtful that the short-circuit current losses were caused by encapsulation browning or obscuration. When we compared the quantum efficiency of a single cell in a degraded module to one from an unexposed control module, it appears that most of the degradation has occurred in the 800 - 1100 nm wave-length region, and not the short wavelength region.
Date: May 1, 2002
Creator: Osterwald, C. R.; Anderberg, A.; Rummel, S. & Ottoson, L.
Partner: UNT Libraries Government Documents Department

Enhanced-Depletion-Width GaInNAs Solar Cells Grown by Molecular-Beam Epitaxy

Description: GaInNAs, potentially useful in a 4-junction GaInP2/GaAs/GaInNAs/Ge solar cell, suffers from very low minority-carrier collection lengths. To date, the currents available from GaInNAs solar cells are not high enough to increase the efficiency of a 3-junction device by adding this fourth junction. Here, we grow p-i-n GaInNAs solar cells by molecular-beam epitaxy with wide, intrinsic base layers and internal quantum efficiencies near 1.0. If similar 1.0-eV GaInNAs junctions can be successfully integrated into the 3-junction structure, the resulting 4-junction cell would have a higher efficiency.
Date: February 1, 2005
Creator: Ptak, A. J.; Friedman, D. J.; Kurtz, S. & Kiehl, J.
Partner: UNT Libraries Government Documents Department

Research Leading to High Throughput Manufacturing of Thin-Film CdTe PV Modules: Annual Technical Report, September 2003-September 2004

Description: First Solar is actively commercializing CdTe-based thin-film photovoltaics. During the past year, major additions of production capability have been completed, as well as process improvements to achieve higher throughput and efficiency and greater durability. This report presents the results of Phase II of the subcontract, entitled ''Research Leading to High Throughput Manufacturing of Thin-Film CdTe PV Modules.'' The subcontract supports several important aspects needed for high-volume manufacturing of high-efficiency modules, including exploration of large-area advanced front-contact window layers, improvements of the semiconductor deposition system, advancement in understanding of post-deposition processing steps and accelerated life testing methods, and progress in the environmental, health and safety programs. Work under this subcontract contributes to the overall manufacturing operation. During Phase II, average module efficiency (total area) on the production line was improved from 7.9% to 8.6% due primarily to process optimization. At the same, time production volume for commercial sales increased from 2.5 MW in 2003 to an estimated 6 MW in 2004. Much of the new 25 MW/yr production line has been qualified, and production volume is steadily increasing.
Date: December 1, 2004
Creator: Powell, R. C.
Partner: UNT Libraries Government Documents Department

High Efficiency Narrow Gap and Tandem Junction Devices: Final Technical Report, 1 May 2002--31 October 2004

Description: The work described in this report uses a modified pulsed plasma-enhanced chemical vapor deposition (PECVD) technique that has been successfully developed to fabricate state-of-the-art nc-Si materials and devices. Specifically, we have achieved the following benchmarks: nc SiH device with an efficiency of 8% achieved at a deposition rate of {approx}1 A/s; nc SiH device with an efficiency of 7% achieved at a deposition rate of {approx}5 A/s; large-area technology developed using pulsed PECVD with uniformity of +/-5% over 25 cm x 35 cm; devices have been fabricated in the large-area system (part of Phase 3); an innovative stable four-terminal (4-T) tandem-junction device of h> 9% fabricated. (Note that the 4-T device was fabricated with existing technology base and with further development can reach stabilized h of 12%); and with improvement in Voc {approx} 650 mV, from the current value of 480 mV can lead to stable 4-T device with h>16%. Toward this objective, modified pulsed PECVD was developed where layer- by-layer modification of nc-SiH has been achieved. (Note that due to budget cuts at NREL, this project was curtailed by about one year.)
Date: March 1, 2005
Creator: Madan, A
Partner: UNT Libraries Government Documents Department

Solar-Grade Silicon from Metallurgical-Grade Silicon Via Iodine Chemical Vapor Transport Purification: Preprint

Description: This conference paper describes the atmospheric-pressure in an ''open'' reactor, SiI2 transfers from a hot (>1100C) Si source to a cooler (>750C) Si substrate and decomposes easily via 2SiI2 Si+ SiI4 with up to 5?m/min deposition rate. SiI4 returns to cyclically transport more Si. When the source is metallurgical-grade Si, impurities can be effectively removed by three mechanisms: (1) differing free energies of formation in forming silicon and impurity iodides; (2) distillation; and (3) differing standard free energies of formation during deposition. Distillation has been previously reported. Here, we focused on mechanisms (1) and (3). We made feedstock, analyzed the impurity levels, grew Czochralski single crystals, and evaluated crystal and photovoltaic properties. Cell efficiencies of 9.5% were obtained. Incorporating distillation (step 2) should increase this to a viable level.
Date: May 1, 2002
Creator: Ciszek, T. F.; Wang, T. H.; Page, M. R.; Bauer, R. E. & Landry, M. D.
Partner: UNT Libraries Government Documents Department