Science and Technology Facility
Solar cell, thin-film, and nanostructure research are conducted in our Science and Technology Facility (S&TF).
Designed specifically to reduce time delays associated with transferring technology to industry, the S&TF's 71,000 square feet is a multi-level facility of lab space, office space, and lobby connected by an elevated bridge to the SERF. The S&TF houses advanced material synthesis, characterization, and general support laboratories.
The S&TF provides numerous capabilities for a wide range of scientific investigations. Many of these capabilities are associated with specific cluster tools for modular deposition, processing, and characterization techniques. The cluster tools are configured around a system using a central robotic arm to transfer samples. Adjacent to the cluster tools is a 3,500-ft2 state-of-the-art cleanroom.
Cluster Tools and Related Capabilities
Photovoltaic Material-Specific Capabilities. Three cluster tools allow R&D on specific photovoltaic materials, which can be deposited, processed, measured, and characterized using the process development and integration approach. Samples can be transferred to additional capabilities via a transport pod. The materials are silicon, copper indium gallium diselenide (CIGS), and cadmium telluride (CdTe).
Measurements and Characterization Capabilities. Some measurement and characterization techniques represent an integrated tool set that uses a robotic transfer chamber to connect capabilities covering electrical/optical, structural/morphological, and chemical/compositional techniques. Other techniques are stand-alone tools for measurements and characterization.
Cross-Cutting Technology Capabilities. The atmospheric processing cluster tool allows scientists to work on processes that do not require high-temperature, high-vacuum conditions. It combines deposition, processing, and characterization techniques that are expanded across material-specific technologies.
Our ISO 5 (class 100) cleanroom has humidity control to maintain superior particulates and process control. The 156-mm silicon wafer toolset includes the following two central features: a Singulus 13-bath, automated wet-bench processing tool, and a Tetreon four-stack diffusion furnace.
Interconnect Process Development Laboratory
Research in thin-film PV is accomplished in this lab with techniques used for monolithic integration of cells into modules. Developing ways to make small, thin-film modules onsite is useful in demonstration purposes. Defining the best ways to use laser and mechanical scribing to make monolithically integrated modules, as well as depositing insulators by spray deposition of nanoparticles helps close the gap between cell and module performance for thin-film PV.
PV Manufacturing Diagnostics Laboratory
Equipment dedicated to the study of PV materials and devices including optical diagnostics, PVScan, and more are available in this lab.
User Characterization Laboratory
Three associated labs under the User Characterization Lab include work in sample preparation, general equipment, and specialized equipment, including a Hall and four-point-probe for electrical analysis, and UV-Vis-NIR spectrophotometers for optical analysis. Most equipment in this lab is operated by a limited user base.
Electro-Optical Diagnostic Development Laboratory
In this lab, researchers collaborate with other research teams in using established in-situ electro-optical characterization techniques to develop new in-situ diagnostics tailored for the specific growth and processing steps used in PV manufacturing. Spectroscopic ellipsometry, photoluminescence, photocurrent decay, reflectometry, Fourier transform infrared, and Raman scattering are experimental techniques used to develop new diagnostic tools directly applicable in manufacturing.
Surface Analysis Laboratory
This lab is used to study and control PV surfaces and interfaces. High-spatial-resolution Auger electron spectroscopy provides essential complementary information on the elemental makeup and distribution in PV films. The XPS/UPS system enables data collection on insulating samples, the probing of both core-level and valence-band electronic structures, and provides information on the chemical environments of specific elements. These capabilities ultimately provide a platform for the study of in-situ real-time control of PV device manufacture.
Analytical Microscopy Laboratory
This lab is used to study PV surface and interface morphologies of interest to the PV community. Scanning probe microscopies and scanning electron microscopy provide real-space characterization of PV material morphologies and electronic structures down to the nanometer scale.
Thin-Film Deposition/Process Development Laboratory
Deposition techniques to deposit various semiconductor layers necessary to form the active junction regions of polycrystalline II-VI devices are conducted in this area of the lab. Deposition processes include close-spaced sublimation, sputtering, and evaporation. Materials include CdS and CdTe, as well as related ternary and quaternary alloys such as CdZnTe, CdSTe, and CdZnSTe. Equipment used to modify properties of deposited films, such as heat-treatment using CdCl2 vapors; development activities related to in-situ process monitoring; and equipment required for substrate cleaning are resources in this lab.
Development of absorber, window, and metal contact thin-film layers for Cu(In,Ga)Se2-based PV devices are performed in this area of the lab. Thin-film layers will be deposited by physical vapor deposition methods and other hybrid methods to integrate improved deposition techniques, critical issues related to the surfaces/interfaces between layers, and in-situ control and diagnostics. Higher-performing solar cells and improved deposition methods for industrial processes are outcomes in this lab.
Contact Process Development Laboratory
In this laboratory, various surface modification and deposition processes are used to develop materials and investigate function of various front- and back-contact schemes for advanced thin-film PV solar cells. Contact materials include metals, semiconductors, and transparent-conducting oxides. Surface-modification processes include semi-automated chemical cleaning for ceramic substrates in a micro-clean environment, as well as in-situ plasma etching and reactive-ion etching within vacuum chambers prior to material deposition. Deposition processes include resistive and electron-beam evaporation, DC and RF sputtering, molecular-beam epitaxy, and chemical-vapor deposition. In-situ surface characterization is used on some equipment including a Kelvin probe for analysis, and residual-gas analysis for information on incorporating trace impurities from the sputtering environment into contact materials.
Wet Chemistry/Electrodeposition Process Development Laboratory
Chemical (wet) processes are used to deposit metal, oxide, and semiconductor thin films for existing programs, as well as research to develop novel processes and materials for next-generation technologies. Routine chemical depositions include CdS and related alloys for use in CdTe and CIGS polycrystalline device technologies. The lab includes apparatus for post-deposition thermal treatment, and equipment to perform inductively coupled plasma spectroscopy required for elemental compositional analysis of bulk and trace impurities.
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