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Development of a Low Cost Insulated Foil Substrate for Cu(InGaSe)2 Photovoltaics

Description: The project validated the use of stainless steel flexible substrate coated with silicone-based resin dielectric, developed by Dow Corning Corporation, for Cu(InGa)Se2 based photovoltaics. The projects driving force was the high performance of Cu(InGa)Se2 based photovoltaics coupled with potential cost reduction that could be achieved with dielectric coated SS web substrate.
Date: January 22, 2012
Creator: Eser, Erten
Partner: UNT Libraries Government Documents Department

Study on the Humidity Susceptibility of Thin-Film CIGS Absorber

Description: The report summarizes the research on the susceptibility of a thermally co-evaporated CuInGaSe2 (CIGS) thin-film absorber to humidity and its consequence on composition, morphology, electrical and electronic properties, and device efficiency.
Date: January 1, 2010
Creator: Pern, F. J.; Egaas, B.; To, B.; Jiang, C. S.; Li, J. V.; Glynn, S. et al.
Partner: UNT Libraries Government Documents Department

Band Gap Energy of Chalcopyrite Thin Film Solar Cell Absorbers Determined by Soft X-Ray Emission and Absorption Spectroscopy

Description: The chemical and electronic structure of high efficiency chalcopyrite thin film solar cell absorbers significantly differs between the surface and the bulk. While it is widely accepted that the absorber surface exhibits a Cu-poor surface phase with increased band gap (Eg), a direct access to the crucial information of the depth-dependency of Eg is still missing. In this paper, we demonstrate that a combination of x-ray emission and absorption spectroscopy allows a determination of Eg in the surface-near bulk and thus complements the established surface- and bulk-sensitive techniques of Eg determination. As an example, we discuss the determination of Eg for a Cu(In,Ga)Se2 absorber [(1.52 +- 0.20) eV].
Date: May 11, 2008
Creator: Bar, M.; Weinhardt, L.; Pookpanratana, S.; Heske, C.; Nishiwaki, S.; Shafarman, W. et al.
Partner: UNT Libraries Government Documents Department

Final Report for Department of Energy/EERE (for public release)

Description: Developing CIGS solar cells calls for the understanding of materials and processing in order to translate the record small efficiency to module and the strategy to produce thin cells for materials and processing saving. This project has exploited nanostructuring of CIG solar cells, including nanowires and nanotextured substrates. We showed that nanowires function as well-defined CIGS-CdS p-n junction for understanding the chemical fluctuation, defect formation interface and grain boundary behaviors and the effect of ion diffusion, which are important but complicated issues for solar cell fabrication. We have also demonstrated effective nanoscale photon management on nanotextured substrate to provide opportunity for thin CIGS solar cells. We also developed the scalable methods for producing such nanotextured substrates. The research output in this project helps advancing the CIGS solar cells and broadly other solar cell technologies in cost reduction per unit power.
Date: April 30, 2012
Creator: Cui, Yi
Partner: UNT Libraries Government Documents Department

High Efficiency Solar Integrated Roof Membrane Product

Description: This project was designed to address the Solar Energy Technology Program objective, to develop new methods to integrate photovoltaic (PV) cells or modules within a building-integrated photovoltaic (BIPV) application that will result in lower installed cost as well as higher efficiencies of the encapsulated/embedded PV module. The technology assessment and development focused on the evaluation and identification of manufacturing technologies and equipment capable of producing such low-cost, high-efficiency, flexible BIPV solar cells on single-ply roofing membranes.
Date: May 15, 2013
Creator: Partyka, Eric & Shenoy, Anil
Partner: UNT Libraries Government Documents Department

Determination of Grain Boundary Charging in Cu(In,Ga)Se2 Thin Films: Preprint

Description: Surface potential mapping of Cu(In,Ga)Se2 (CIGS) thin films using scanning Kelvin probe force microscopy (SKPFM) aims to understand the minority-carrier recombination at the grain boundaries (GBs) of this polycrystalline material by examining GB charging, which has resulted in a number of publications. However, the reported results are highly inconsistent. In this paper, we report on the potential mapping by measuring wide-bandgap or high-Ga-content films and by using a complementary atomic force microscopy-based electrical technique of scanning capacitance microscopy (SCM). The results demonstrate consistent, positively charged GBs on our high-quality films with minimal surface defects/charges. The potential image taken on a low-quality film with a 1.2-eV bandgap shows significantly degraded potential contrast on the GBs and degraded potential uniformity on grain surfaces, resulting from the surface defects/charges of the low-quality film. In contrast, the potential image on an improved high-quality film with the same wide bandgap shows significantly improved GB potential contrast and surface potential uniformity, indicating that the effect of surface defects is critical when examining GB charging using surface potential data. In addition, we discuss the effect of the SKPFM setup on the validity of potential measurement, to exclude possible artifacts due to improper SKPFM setups. The SKPFM results were corroborated by using SCM measurements on the films with a CdS buffer layer. The SCM image shows clear GB contrast, indicating different electrical impedance on the GB from the grain surface. Further, we found that the GB contrast disappeared when the CdS window layer was deposited after the CIGS film was exposed extensively to ambient, which was caused by the creation of CIGS surface defects by the ambient exposure.
Date: June 1, 2012
Creator: Jiang, C. S.; Contreras, M. A.; Repins, I.; Moutinho, H. R.; Noufi, R. & Al-Jassim, M. M.
Partner: UNT Libraries Government Documents Department

Spray Deposition of High Quality CuInSe2 and CdTe Films: Preprint

Description: A number of different ink and deposition approaches have been used for the deposition of CuInSe2 (CIS), Cu(In,Ga)Se2 (CIGS), and CdTe films. For CIS and CIGS, soluble precursors containing Cu, In, and Ga have been developed and used in two ways to produce CIS films. In the first, In-containing precursor films were sprayed on Mo-coated glass substrates and converted by rapid thermal processing (RTP) to In2Se3. Then a Cu-containing film was sprayed down on top of the In2Se3 and the stacked films were again thermally processed to give CIS. In the second approach, the Cu-, In-, and Ga-containing inks were combined in the proper ratio to produce a mixed Cu-In-Ga ink that was sprayed on substrates and thermally processed to give CIGS films directly. For CdTe deposition, ink consisting of CdTe nanoparticles dispersed in methanol was prepared and used to spray precursor films. Annealing these precursor films in the presence of CdCl2 produced large-grained CdTe films. The films were characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM). Optimized spray and processing conditions are crucial to obtain dense, crystalline films.
Date: May 1, 2008
Creator: Curtis, C. J.; van Hest, M.; Miedaner, A.; Leisch, J.; Hersh, P.; Nekuda, J. et al.
Partner: UNT Libraries Government Documents Department

Investigation of the Effect of I-ZnO Window Layer on the Device Performance of the Cd-Free CIGS Based Solar Cells: Preprint

Description: This paper focuses on preparing Cd-free, CIGS-based solar cells with intrinsic high resistivity ZnO (I-ZnO) films deposited by metal-organic chemical vapor deposition (MOCVD) technique at different deposition substrate temperature and I-ZnO film thickness, and the effect of the prior treatment of CIGS films by ammonium hydroxide (NH4OH) diluted solution on the device performance.
Date: May 1, 2008
Creator: Hasoon, F. S.; Al-Thani, H. A.; Li, X.; Kanevce, A.; Perkins, C. & Asher, S.
Partner: UNT Libraries Government Documents Department

Damp-Heat Induced Degradation of Transparent Conducting Oxides for Thin-Film Solar Cells: Preprint

Description: The stability of intrinsic and Al-doped single- and bi-layer ZnO for thin-film CuInGaSe2 solar cells, along with Al-doped Zn1-xMgxO alloy and Sn-doped In2O3 (ITO) and F-doped SnO2, was evaluated by direct exposure to damp heat (DH) at 85oC and 85% relative humidity. The results show that the DH-induced degradation rates followed the order of Al-doped ZnO and Zn1-xMgxO >> ITO > F:SnO2. The degradation rates of Al:ZnO were slower for films of higher thickness, higher substrate temperature in sputter-deposition, and with dry-out intervals. As inferred from the optical micro-imaging showing the initiation and propagation of degrading patterns and regions, the degradation behavior appears similar for all TCOs, despite the obvious difference in the degradation rate. A degradation mechanism is proposed to explain the temporal process involving thermal hydrolysis.
Date: May 1, 2008
Creator: Pern, F. J.; Noufi, R.; Li, X.; DeHart, C. & To, B.
Partner: UNT Libraries Government Documents Department

Cost and Reliability Improvement for CIGS-Based PV on Flexible Substrate: May 24, 2006 -- July 31, 2010

Description: Global Solar Energy rapidly advances the cost and performance of commercial thin-film CIGS products using roll-to-roll processing on steel foil substrate in compact, low cost deposition equipment, with in-situ sensors for real-time intelligent process control. Substantial increases in power module efficiency, which now exceed 13%, are evident at GSE factories in two countries with a combined capacity greater than 75 MW. During 2009 the average efficiency of cell strings (3780 cm2) was increased from 7% to over 11%, with champion results exceeding 13% Continued testing of module reliability in rigid product has reaffirmed extended life expectancy for standard glass product, and has qualified additional lower-cost methods and materials. Expected lifetime for PV in flexible packages continues to increase as failure mechanisms are elucidated, and resolved by better methods and materials. Cost reduction has been achieved through better materials utilization, enhanced vendor and material qualification and selection. The largest cost gains have come as a result of higher cell conversion efficiency and yields, higher processing rates, greater automation and improved control in all process steps. These improvements are integral to this thin film PV partnership program, and all realized with the 'Gen2' manufacturing plants, processes and equipment.
Date: May 1, 2011
Creator: Wiedeman, S.
Partner: UNT Libraries Government Documents Department

CIGS P1, P2, P3 Scribing Processes using a Pulse Programmable Industrial Fiber Laser: Preprint

Description: We describe a novel set of laser processes for the CIGS P1, P2 and P3 scribing steps, the development of which has been enabled by a unique pulse-programmable fiber laser. We find that the unique pulse control properties of this 1064 nm wavelength laser have significant effects on the material removal dynamics of the various film layers in the CIGS material system. In the case of the P2 and P3 processes, the shaped pulses create new laser/material interaction effects that permit the material to be cleanly and precisely removed with zero Heat Affected Zone (HAZ) at the edges of the scribe. The new P2 and P3 processes we describe demonstrate the first use of infrared nanosecond laser pulses that eliminate the HAZ and the consequent localized compositional changes in the CIGS absorber material that result in poor shunt resistance. SEM micrographs and EDX compositional scans are presented. For the P1 scribe, we process the bi-layer molybdenum from the film side as well as through the glass substrate. Microscopic inspection and compositional analysis of the scribe lines are not sufficient to determine electrical and optical performance in working PV modules. Therefore, to demonstrate the applicability of the infrared pulse-programmable laser to all three scribing processes for thin-film CIGS, we fabricate small-size multiple-cell monolithically interconnected mini-modules in partnership with the National Renewable Energy Laboratory (Golden, Colorado). A total of four mini-modules are produced, two utilizing all laser scribing, and two with the P2 and P3 steps mechanically scribed (by a third party) for reference. Mini-module performance data measured at NREL is presented, and we also discuss the commercialization potential of the new single-laser CIGS scribing process. Finally we present a phenomenological model to describe this physics underlying this novel ablation process.
Date: October 1, 2010
Creator: Rekow, M.; Murison, R.; Panarello, T.; Dunsky, C.; Dinkel, C.; Nikumb, S. et al.
Partner: UNT Libraries Government Documents Department

High Performance CIGS Thin-Film Solar Cells: A Laboratory Perspective

Description: We present a summary of our work on the preparation of CuInGaSe2 (CIGS) absorbers that has led to fabricating record-efficiency solar cells. The use of the three-stage process in conjunction with composition monitoring facilitates the fabrication of solar cells with efficiencies between 18% and 19.5% for absorber bandgap in the range of 1.1-1.2 eV. We describe our recent results in reducing absorber thickness and low-temperature deposition. Our preliminary results on absorbers grown from low-purity source materials show promise of reducing the cost of fabricating the absorber.
Date: November 1, 2005
Creator: Ramanathan, K.; Bhattacharya, R.; Contreras, M.; Keane, J. C.; To, B.; Dhere, R. G. et al.
Partner: UNT Libraries Government Documents Department

Device physics of thin-film polycrystalline cells and modules. Annual subcontract report, December 6, 1994--December 5, 1995

Description: This report describes the work on a number of projects carried out at both the cell and the module level during the past year. We investigated the effects of CdS thickness in collaboration with six CdTe cell-fabrication laboratories; there appears to be a critical thickness, between 500 and 1000 {Angstrom} depending on fabrication process, below which junction quality is degraded. Our experimental and modeling project showed that conduction-band offsets less than about 0.3 eV have little effect on the performance of a CuInSe{sub 2} (CIS) or CdTe cell under the traditional assumption that the absorber material accounts for most of the depletion region. The work in several other cell projects included the role of Ga distribution in Cu{sub 1-x}Ga{sub x}Se{sub 2} (CIGS) cells, changes that occur in some cells over time, optical characterization of commonly used CdTe substrates and front contacts, and comparative characterization of CIGS cells where identical absorbers were combined with variations in window fabrication. Our work on the primary module-characterization project developed the successful use of chopping-frequency variation in a scanning beam to separate photocurrent and shunting problems affecting individual cells of an encapsulated module. Other module projects included modifications in analysis required by the typical module-cell geometry, the practical effect of nonuniformities in light intensity or cell temperature, and the advantages and pitfalls of forward bias across a module during a light scan.
Date: August 1, 1996
Creator: Sites, J.R.
Partner: UNT Libraries Government Documents Department

Recent Progress in CIGS Thin Film Solar Cell Research at NREL: Preprint

Description: Presented at the 2001 NCPV Program Review Meeting: This paper summarizes our work toward improving reproducibility in fabricating high efficiency absorbers and devices. This paper summarizes our work toward improving reproducibility in fabricating high efficiency absorbers and devices. This resulted in the fabrication of a CIGS cell with an efficiency of 21% under concentrated light. We compare devices fabricated with CdS and with Cd solution treatment alone. A high conversion efficiency of 15.7% is obtained with the latter, and we attribute this to the n-type doping afforded by Cd. The work is extended to absorbers provided by Siemens Solar Industries (SSI).
Date: October 1, 2001
Creator: Ramanathan, K.; Hasoon, F. S.; Al-Thani, H.; Alleman, J.; Keane, J.; Dolan, J. et al.
Partner: UNT Libraries Government Documents Department

Thin-Film CIGS Photovoltaic Technology: Annual Technical Report-Phase II, 16 April 1999-15 April 2000

Description: A summary of Energy Photovoltaics' Phase II work includes the following: (1) EPV has demonstrated that it can sputter a Mo back-contact capable of supporting very high efficiency cell processing. Using EPV Mo, NREL has deposited a 17.1% CIGS cell (no AR coating). EPV believes it can identify the signature of ``good'' Mo. The Mo was produced on EPV's 0.43 m{sup 2} pilot-line equipment; (2) EPV has performed compound synthesis for several classes of materials, namely non-Cu precursor materials, Cu-containing materials, and ternary buffer materials. Using a ternary compound synthesized at EPV (ZIS) as an evaporation source material for the buffer layer, a Cd-free CIGS device has been produced having an efficiency of 11.5% (560 mV, 32.1 mA/cm{sup 2}, FF 64.3%). The ZIS films are photoconductive, and the devices exhibit no dark-light crossover or light soaking effects; (3) EPV initiated the interest of the University of Oregon in capacitance spectroscopy of CIGS devices. An Urbach tail with characteristic energy E0 < 20meV was identified by transient photocapacitance spectroscopy; (4) Small-area CIGS devices were produced in the pilot-line system with an efficiency of 12.0% (581 mV, 30.1 mA/cm{sup 2}, FF 68.7%), and in an R and D-scale system with 13.3% efficiency (569 mV, 34.1 mA/cm{sup 2}, FF 68.1%); (5) An improved linear evaporation source for Cu delivery has been developed and was used for CIGS formation in the pilot-line system. The deposition width is 45 cm. This technological ``tour de force'' allows EPV to build large-area CIGS systems possessing considerable flexibility. In particular, both EPV's FORNAX process and NREL's 3-stage process have been implemented on the pilot line. A CIGS thickness uniformity of 7% over a 40 cm width has been achieved; (6) A 4-head linear source assembly was designed, constructed, and is in use. Flux monitoring is practiced; (7) Large-area ...
Date: August 24, 2000
Creator: Delahoy, A.E.; Bruns, J.; Ruppert, A.; Akhtar, M.; Chen, L. & Kiss, Z.J.
Partner: UNT Libraries Government Documents Department

Photovoltaic manufacturing cost and throughput improvements for thin-film CIGS-based modules: Phase 1 technical report, July 1998--July 1999

Description: The primary objectives of the Global Solar Energy (GSE) Photovoltaic Manufacturing Technology (PVMaT) subcontract are directed toward reducing cost and expanding the production rate of thin-film CuInGaSe{sub 2} (CIGS)-based PV modules on flexible substrates. Improvements will be implemented in monolithic integration, CIGS deposition, contact deposition, and in-situ CIGS control and monitoring. In Phase 1, GSE has successfully attacked many of the highest risk aspects of each task. All-laser, selective scribing processes for CIGS have been developed, and many end-of-contract goals for scribing speed have been exceeded in the first year. High-speed ink-jet deposition of insulating material in the scribes now appears to be a viable technique, again exceeding some end-of-contract goals in the first year. Absorber deposition of CIGS was reduced corresponding to throughput speeds of up to 24-in/min, also exceeding an end-of-contract goal. Alternate back-contact materials have been identified that show potential as candidates for replacement of higher-cost molybdenum, and a novel, real-time monitoring technique (parallel-detector spectroscopic ellipsometry) has shown remarkable sensitivity to relevant properties of the CIGS absorber layer for use as a diagnostic tool. Currently, one of the bilayers has been baselined by GSE for flexible CIGS on polymeric substrates. Resultant back-contacts meet sheet-resistance goals and exhibit much less intrinsic stress than Mo. CIGS has been deposited, and resultant devices are comparable in performance to pure Mo back-contacts. Debris in the chamber has been substantially reduced, allowing longer roll-length between system cleaning.
Date: March 1, 2000
Creator: Wiedeman, S. & Wendt, R.G.
Partner: UNT Libraries Government Documents Department

Performance Characterization and Remedy of Experimental CuInGaSe2 Mini-Modules: Preprint

Description: We employed current-voltage (I-V), quantum efficiency (QE), photoluminescence (PL), electroluminescence (EL), lock-in thermography (LIT), and (electrochemical) impedance spectroscopy (ECIS) to complementarily characterize the performance and remedy for two pairs of experimental CuInGaSe2 (CIGS) mini-modules. One pair had the three scribe-lines (P1/P2/P3) done by a single pulse-programmable laser, and the other had the P2/P3 lines by mechanical scribe. Localized QE measurements for each cell strip on all four mini-modules showed non-uniform distributions that correlated well with the presence of performance-degrading strips or spots revealed by PL, EL, and LIT imaging. Performance of the all-laser-scribed mini-modules improved significantly by adding a thicker Al-doped ZnO layer and reworking the P3 line. The efficiency on one of the all-laser-scribed mini-modules increased notably from 7.80% to 8.56% after the performance-degrading spots on the side regions along the cell array were isolated by manual scribes.
Date: July 1, 2011
Creator: Pern, F. J.; Yan, F.; Mansfield, L.; Glynn, S.; Rekow, M. & Murion, R.
Partner: UNT Libraries Government Documents Department

Improved Solar Cell Efficiency Through the Use of an Additive Nanostructure-Based Optical Downshifter: Final Subcontract Report, January 28, 2010 -- February 28, 2011

Description: This final report summarizes all SpectraWatt's progress in achieving a boost in solar cell efficiency using an optical downshifter. Spectrawatt's downshifting technology is based on a nanostructured material system which absorbs high energy (short wavelength) light and reemits it at a lower energy (long wavelength) with high efficiency. This system has shown unprecedented performance parameters including near unity quantum yield and high thermal stability.
Date: May 1, 2011
Creator: Kurtin, J.
Partner: UNT Libraries Government Documents Department