Herbert C. Ovshinsky

Amorphous Silicon Alloy Photovoltaic Technology - from R&D to Production

The key requirements for photovoltaic modules to be accepted for large-scale terrestrial applications are (i) low material cost, (ii) high efficiency with good stability, (iii) low manufacturing cost with good yield and (iv) environmental safety. Thin films of amorphous silicon alloy are inexpensive; the products are also environmentally benign. The challenge has been to improve the stable efficiency of these modules and transfer the R&D results into production. Using a Multijunction, Multi-bandgap approach to capture the solar spectrum more efficiently, we have developed one-square-foot modules with initial efficiency of 11.8%. After 1000 h of one-sun light soaking, a stable efficiency of 10.2% was obtained. Both the efficiency values were confirmed by National Renewable Energy Laboratory. The technology has been transferred to production using an automated roll-to-roll process in which different layers of the cell structure are deposited in a continuous manner onto stainless steel rolls, 14” wide and half a mile long. The rolls are next processed into modules of different sizes. This inexpensive manufacturing process produces high efficiency modules with subcell yields greater than 99%. The key features of the technology transfer and future scope for improvement are discussed.

Triple-junction amorphous silicon alloy PV manufacturing plant of 5 MW annual capacity

A spectral-splitting, triple-junction a-Si alloy solar cell processor has been designed, built and optimized. A roll-to-roll process has been used to deposit two layers of back reflector, a triple-cell structure with nine layers of a-Si and a-SiGe alloys and a single layer of antireflection coating consecutively on a half-a-mile roll of stainless steel. The coated web is next slabbed and processed to make a variety of products. The design of the machine and processes used incorporate several key features developed for improving cell efficiency. In order to reduce manufacturing cost, higher deposition rates and thinner cells than are used in R&D have been used. The back reflector also consists of Al/ZnO rather than Ag/ZnO. Large-scale production has begun, and products are being shipped for a wide range of applications.

Continuous roll‐to‐roll amorphous silicon photovoltaic manufacturing technology

Energy Conversion Devices, Inc. (ECD) has designed and constructed a 2 Megawatt (mW) manufacturing line that produces triple‐junction spectrum‐splitting a‐Si alloy solar cells in a continuous roll‐to‐roll process. This manufacturing line has reliably and consistently produced high efficiency solar cells. We have demonstrated the production of 4ft 2 triple‐junction two band‐gap a‐Si alloy PV production modules with 8% stable aperture area efficiency. The production line has successfully incorporated: 1) a band‐gap profiled a‐Si‐Ge narrow band‐gap solar cell deposited in a continuous roll‐to‐roll process using a proprietary gas distribution manifold and cathode configuration; and 2) a textured Ag/ZnO back‐reflector deposited in a continuous roll‐to‐roll sputtering machine with production subcell yields greater than 99%.

Use of gas jet deposition technique to prepare a-Si:H solar cells

We have tested the feasibility of using a new gas jet deposition technique to deposit hydrogenated amorphous silicon (a-Si:H) i-layers for solar cells at high deposition rates. With this technique, a source gas flow is forced at high speeds through a jet nozzle pointed at the heated substrate surface. Before reaching the substrate surface, the gas is activated by an electron beam which produces radicals which deposit on the substrate surface forming the thin film. We have prepared single-junction a-Si:H n-i-p cells with 9.4% and 8.7% efficiencies at i-layer deposition rates of 2 /spl Aring//s and 5 /spl Aring//s, respectively. Initial light soaking results suggest that these cells are as stable as those having the same i-layer thickness prepared using the PECVD technique. We plan to further develop this new deposition technique to demonstrate that a-Si:H and a-SiGe:H cells can be prepared at faster deposition rates with even higher stable efficiencies.

Continuous roll-to-roll a-Si PV module manufacturing

Significant progress has been made recently at ECD (Energy Conversion Devices, Inc.), in developing new manufacturing technologies for a‐Si (amorphous silicon) photovoltaics. In a 2 MW continuous roll‐to‐roll a‐Si PV (photovoltaics) manufacturing plant, designed and constructed by ECD, we have advanced ECD’s PV technology and demonstrated the manufacturing of 4 ft2 PV modules with 9.5% initial and 8% stable efficiencies. In addition, high subcell yield up to 99.7% has been demonstrated in 600 m long (about 15 kWp) production runs with high uniformity and consistency. ECD has recently designed and constructed an additional pilot manufacturing machine to develop new technologies including high throughput serpentine web continuous roll‐to‐roll deposition of a‐Si alloy materials. When it is incorporated into a large‐scale production line, serpentine technology can maximize the throughput for a high volume production plant, reduce the machine cost, improve the gas utilization, reduce power consumption, and imp...

Production start-up of 2 MW a-Si PV manufacturing line at Sovlux plant

We report the results of production start-up efforts at the 2 MW Sovlux photovoltaic production line. Triple-junction solar cells with higher than 10% initial efficiency were produced in this production line with subcell yield up to 96%. The production process demonstrated high reproducibility and consistency from run to run. 2 ft/sup 2/ and 4 ft/sup 2/ modules assembled in the Sovlux plant using these solar cell material have demonstrated an initial efficiency of 9.4%. The solar cell material produced in Sovlux was also shipped to ECD to assemble large area 1.3 ft. by 20 ft. rooftop modules. Lightweight, flexible rooftop modules with initial efficiency up to 9.3% were produced at a high yield.

PV Mat Manufacturing Improvements for Continuous Roll-to-Roll Amorphous Silicon Module Production

Under the PVMat 2A Program, Energy Conversion Devices, Inc. (ECD) has performed manufacturing technology development work utilizing its proprietary continuous roll-to-roll triple-junction a-Si alloy solar cell production line. Among the accomplishments achieved under this program, ECD demonstrated the production of the world’s first 4 ft2 PV modules utilizing triple-junction two-bandgap solar cells manufactured in a commercial, continuous roll-to-roll production line. These 4 ft2 modules had 9.5% initial efficiency and 8% stable module efficiency. ECD has recently designed and constructed a 5 MW continuous roll-to-roll a-Si solar cell processor for its U.S. joint venture, United Solar Systems Corp. (United Solar). The state-of-the-art processor incorporates major advances in solar cell design and manufacturing processes achieved by United Solar and ECD, with support from DOE/NREL. The advanced continuous roll-to-roll triple-junction a-Si module production technology will reduce module production costs, in...