Electricity from photovoltaic solar cells: Flat-Plate Solar Array Project final Report. Volume III: Silicon sheet: wafers and ribbons

The Flat-Plate Solar Array (FSA) Project, funded by the U.S. Government and managed by the Jet Propulsion Laboratory, was formed in 1975 to develop the module/array technology needed to attain widespread terrestrial use of photovoltaics by 1985. To accomplish this, the FSA Project established and managed an Industry, University, and Federal Government Team to perform the needed research and development. The primary objective of the Silicon Sheet Task of the FSA Project was the development of one or more low-cost technologies for producing silicon sheet suitable for processing into cost-eompetitive solar cells. Silicon sheet refers to high-purity crystalline silicon of size and thickness for fabrication into solar cells. The Task effort began with state-of-the-art sheet technologies and then solicited and supported any new silicon sheet alternatives that had the potential to achieve the Project goals. A total of 48 contracts were awarded that covered work in the areas of ingot growth and casting, wafering, ribbon growth, other sheet technologies, and programs of supportive research. Periodic reviews of each sheet technology were held, assessing the technical progress and the long-range potential. Technologies that failed to achieve their promise, or seemed to have lower probabilities for success in comparison with others, were dropped. A series of workshops was initiated to assess the state of the art, to provide insights into problems remaining to be addressed, and to support technology transfer. The Task made and fostered significant improvements in silicon sheet including processing of both ingot and ribbon technologies. An additional important outcome was the vastly improved understanding of the characteristics associated with high-quality sheet, and the control of the parameters required for higher efficiency solar cells. Although significant sheet cost reductions were made, the technology advancements required to meet the Task cost goals were not achieved. This FSA Final Report (JPL Publication 86-31, 5101-289, DOE/JPL 1012-125, October 1986) is composed of eight volumes, consisting of an Executive Summary and seven technology reports: Volume I: Executive Summary. Volume II: Silicon Material. Volume III: Silicon Sheet: Wafers and Ribbons Volume IV: High-Efficiency Solar Celis. Volume V: Process Development. Volume VI: Engineering Sciences and Reliability. Volume VII: Module Encapsulation. Volume VIII: Project Analysis and Integration. Two supplemental reports included in the final report package are: FSA Project: 10 Years of Progress, JPL Document 400-279. 5101-279, October 1985. Summary of FSA Project Documentation: Abstracts of Published Documents, 1975 to 1986, JPL Publication 82-79 (Revision 1),5101-221, DOE/JPL-1 012-76, September 1986

Silicon ingot casting: Heat Exchange Method (HEM). Multi-wire slicing: Fixed Abrasive Slicing Technique (FAST). Phase 3 and phase 4: Silicon sheet growth development for the large area sheet task of the low-cost solar array project

Several areas of silicon sheet growth development are addressed including: silicon ingot casting, heat exchanger method, multiwire slicing, and fixed abrasive slicing technique

Carbon Nitride and Conjugated Polymer Composite Materials

The semiconductor and photovoltaic properties of carbon nitride (CNx) thin films prepared using a reactive magnetron sputtering technique were investigated both individually and as composites with the organic conjugated polymers polybithiophene (PBT) and poly(3-hextlthiophene) (P3HT). At low nitrogen content, the film structure was dominated by graphitic sp2 percolation networks, whereas at higher nitrogen contents CNx films started to demonstrate semiconductor properties, as evidenced by the occurrence of photoconductivity and the development of a space charge region. When CNx was deposited onto a PBT substrate, it was found to function as an acceptor material improving the photocurrent generation both in solution and in solid state photovoltaic devices, with the external quantum efficiencies reaching 1% at high nitrogen contents. The occurrence of the donor–acceptor charge transfer was further evidenced by suppression of the n-doping of the PBT polymer by CNx. Nanoscale atomic force microscopy (AFM) and current-sensing AFM data suggested that CNx may form a bulk heterojunction with PBT. Thermal annealing of nitrogen rich CNx films led to n-type semiconductor materials consisting of a graphitic carbon nitride network as determined using X-ray photoelectron spectroscopy, and these materials exhibited photovoltaic properties. Intensity modulated photocurrent (IMPS) and photovoltage (IMVS) spectroscopies were used to study the mechanism of photoprocesses in P3HT:PCBM ([6,6]-phenyl C61 butyric acid methyl ester ) bulk heterojunction organic solar cells at various light intensities. The use of the frequency domain techniques allowed us to separate the bulk and interfacial processes and gain valuable insight into the mechanism of losses in these devices. The results provide direct evidence that interfacial nongeminate recombination is one of the dominant loss and aging mechanisms in bulk heterojunction organic solar cells. The trapping of photoexcited holes in the P3HT phase was found to contribute to the increased recombination rate. It was determined that interfacial recombination occurs at the P3HT/PCBM interface and that higher PCBM contents help to improve charge carrier extraction. The results suggest that promising ways of improving the efficiency of bulk heterojunction solar cells may be reducing the charge trapping both at and near the P3HT:PCBM interface, as well as improving the efficiency of charge extraction at the contacts

Properties of High Nitrogen Content Carbon Nitride Thin Films Prepared by a Radio Frequency Magnetron Sputtering Deposition Technique

The properties of carbon nitride (CNx) films deposited onto various substrates using a radiofrequency magnetron sputtering technique were studied as a function of deposition parameters, especially magnetron power, gas pressure and nitrogen content in the plasma. Indium tin oxide (ITO) coated glass and fluorine tin oxide (FTO) coated glass as well as metal substrates (silver and tungsten) were used. Scanning electron microscopy (SEM) was used to study the surface morphology of the prepared CNx films. Energy-dispersive X-ray spectroscopy (EDX) as well as survey X-ray photoelectron spectroscopy (XPS) spectra were used to perform the elemental analysis of the CNx films. Ultraviolet-visible (UV-Vis) spectrophotometry was conducted to study CNx films on ITO glass to characterize the absorption spectrum and thickness of the film, as well as estimate the material\u27s band gap. Schottky cells were created using either ITO or FTO coated glass as the substrate, CNx films as the active material, and aluminum as the counter electrode. Current-voltage, current-time, and voltage-time plots were used to demonstrate the photovoltaic effect in the samples, as well as to show the benefits of ageing and annealing to the cell’s performance. Different annealing conditions were explored to try and remove the high levels of oxygen that were found in the CNx films in an attempt to increase the open circuit voltage of the cells. It was concluded that oxygen comes from conducting metal oxides (ITO/FTO) during the film deposition process. Therefore, metal contacts (silver and tungsten) were subsequently used instead of ITO or FTO glass which resulted in low oxygen CNx films. The bonding patterns in CNx films were determined using high-resolution XPS as a function of deposition parameters as well as annealing. It was found that the films contained a significant amount of pyridinic moieties, which increased upon annealing. On the contrary, the contribution of quaternary nitrogen, which is the main n-doping configuration in carbon nitride, was quite small and further decreased with annealing. The XPS results allowed us to shed light on the nature of photoactivity demonstrated by high nitrogen content carbon nitride films

Film Fabrication Technologies at NREL

The National Renewable Energy Laboratory (NREL) has extensive capabilities for fabricating a variety of high-technology films. Much of the in-house work in NREL's large photovoltaics (PV) program involves the fabrication of multiple thin-film semiconducting layers constituting a thin-film PV device. NREL's smaller program in superconductivity focuses on the fabrication of superconducting films on long, flexible tape substrates. This paper focuses on four of NREL's in-house research groups and their film fabrication techniques, developed for a variety of elements, alloys, and compounds to be deposited on a variety of substrates. As is the case for many national laboratories, NREL's technology transfer efforts are focusing on Cooperative Research and Development Agreements (CRADA's) between NREL researchers and private industry researchers

Nickel oxide photocathodes prepared using rapid discharge sintering for p-type dye-sensitized solar cells

This paper compares the photoelectrochemical performances of nickel oxide (NiO) thin films processed using two different sintering procedures: rapid discharge sintering (RDS) and conventional furnace sintering (CS). Prior to sintering, NiO nanoparticles were sprayed onto substrates to form loosely adherent nanoparticulate coatings. After RDS and furnace sintering the resultant NiO coatings were sensitized with erythrosine B dye and corresponding p-type dyesensitized solar cells were fabricated and characterized. NiO electrodes fabricated using the RDS technique exhibited a fourfold enhancement in electroactivity compared to CS electrodes. A possible explanation is the smaller sintered grain size and more open mesoporous structure achieved using the microwave plasma treatments

Progress in Nanoporous Templates: Beyond Anodic Aluminum Oxide and Towards Functional Complex Materials

Successful synthesis of ordered porous, multi-component complex materials requires a series of coordinated processes, typically including fabrication of a master template, deposition of materials within the pores to form a negative structure, and a third deposition or etching process to create the final, functional template. Translating the utility and the simplicity of the ordered nanoporous geometry of binary oxide templates to those comprising complex functional oxides used in energy, electronic, and biology applications has been met with numerous critical challenges. This review surveys the current state of commonly used complex material nanoporous template synthesis techniques derived from the base anodic aluminum oxide (AAO) geometry