Masatsugu Izu

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.

VHF Plasma Deposition of μc-Si p-Layer Materials

Microcrystalline silicon (μc-Si) p-layers have been widely used in amorphous silicon (a-Si) solar cell research and manufacturing to achieve record high solar cell efficiency. In order to further improve the solar cell performance and achieve wider parameter windows for the process conditions, we studied the deposition of high quality μc-Si p-layer material using a very high frequency (VHF) plasma enhanced CVD process. A design of experiment (DOE) approach was used for the exploration and optimization of deposition parameters. The usage of DOE leads to a quick optimization of the deposition process within a short time frame. In addition, by using a modified VHF deposition process, we have improved the solar cell blue response which leads to a 6–10% improvement in the solar cell efficiency. Such an improvement is likely due to an improved microcrystalline formation in the p-layer.

Stability Test Of 4 Ft2 Triple-Junction a-Si Alloy PV Production Modules

We report results of stability tests of 4 ft 2 triple-junction a-Si alloy photovoltaic (PV) Modules. These Modules were produced in ECDs 2 Megawatt (MW) continuous, roll-to-roll PV Manufacturing line during the early stage of optimization. The stable module efficiency after 600 hours of 1 sun light soaking at approximately 50°C under load, is 8%. This is the highest stable efficiency for large area (≥4 ft 2 ) a-Si alloy PV Modules Made in a production line.

Improved /spl mu/c-Si p-layer and a-Si i-layer materials using VHF plasma deposition

Microcrystalline Si p-layers have been widely used in a-Si solar cell technology to achieve high efficiency. To improve the solar cell performance further, the authors have studied the deposition of high quality /spl mu/c-Si p-layer material using a modified VHF plasma enhanced CVD process and consequently have improved the solar cell current. This improvement was primarily in the blue response which leads to a 6-10% improvement in the overall solar cell efficiency. In addition, they have explored the deposition of a-Si at high rates using VHF plasma and compared these VHF i-layers with RF plasma deposited i-layers. With improved deposition conditions, VHF intrinsic layers deposited at a rate up to 15 /spl Aring//s show similar device performance and light stability to VHF and RF i-layers deposited at low rates and show higher stability than RF i-layers deposited at high rates in the same deposition system. A 10.9% efficient single-junction solar cell was fabricated using a VHF deposited i-layer.

Use of a gas jet deposition technique to prepare microcrystalline Si solar cells

A gas jet deposition technique has been used to prepare microcrystalline Si (/spl mu/c-Si) i-layers for nip solar cells at rates of 15 /spl Aring//s. The red light absorbing capabilities make these cells an attractive alternative to a-SiGe in high efficiency multi-junction structures. The high deposition rates allow for fabrication of the required thick /spl mu/c-Si i-layers in a similar amount of time to those used for high quality a-SiGe i-layers (rates of 1-3 /spl Aring//s). Using a 610 nm cutoff filter which only allows red light to strike the device, pre-light soaked short circuit currents of 8-10 mA/cm/sup 2/ and 2.7% red-light efficiencies have been obtained while AM1.5 white light efficiencies are above 7%. These efficiencies on average degrade only by 2% (stabilized efficiencies of 2.6%) after long-term light soaking (1000 hrs.). This small amount of degradation compares with the 15-17% degradation in efficiencies for a-SiGe cells subjected to similar irradiation treatments (final light-soaked red light efficiencies of 3.2%). Using the /spl mu/c-Si nip structure as the bottom cell of an a-Si//spl mu/c-Si tandem-junction cell, pre-light soaking AM1.5 efficiencies of 9.8% have been achieved.

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.

a-Si:H-based triple-junction cells prepared at i-layer deposition rates of 10 a/s using a 70 MHz PECVD technique

Using a 70 MHz VHF PECVD technique to prepare all of the i-layers at deposition rates near 10 /spl Aring//s, a-Si:H/a-SiGe:H/a-SiGe:H triple-junction cells have been fabricated and initial active area AM1.5 efficiencies of 11% (total area efficiencies of 10-10.3%) have been achieved. After 700 hrs, of light soaking of one sun light soaking, the cell efficiencies degrade to 9.6% with a percentage of degradation of 10-14%, a percentage typical of what is obtained for high efficiency triple-junction cells prepared using i-layer deposition rates near 1 /spl Aring//s. A major challenge toward further improving the efficiencies is the fabrication of a-SiGe:H i-layers at 10 a/s with the quality of those made using the standard 13.56 MHz, 1 /spl Aring//s method. Deposition conditions that lead to less polyhydride formation during a-SiGe:H growth would likely lead to improved performance for the triple-junction cells.

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...

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...

Preparation of a-Si:H and a-SiGe:H nip cells at high rates using a 70 MHz VHF PECVD technique

A 70 MHz Very High Frequency (VHF) Plasma Enhanced Chemical Vapor Deposition (PECVD) technique has been used to prepare i-layers for small area, single-junction a-Si:H and a-SiGe:H nip cells and triple-junction devices at deposition rates as high as 10 A/s. For both the a-Si:H and a-SiGe:H single-junction cells under optimized deposition conditions, the efficiencies and the light stability remain relatively constant as the i-layer deposition rate is varied from 1 to 10 A/s. Also the stable efficiencies for both types of cells are similar to those for similar cells made in the same deposition system at low deposition rates (1 A/s) using the standard 13.56 MHz PECVD technique. Triple-junction a-Si:H/a-SiGe:H/a-SiGe:H cells have been fabricated using the VHF technique to prepare all of the i-layers at deposition rates near 10 A/s. These devices have pre-light soaked active area efficiencies between 9.5 and 10% and total area efficiencies between 9.0 and 9.5%. Considering these results, the VHF method is a pr...