Joachim Doehler

Order Parameters in a -Si Systems

THE AMORPHOUS-CRYSTALLINE transition in a-Si and a-Ge has been studied for many years [1,2]. However, unlike electrical and optical properties, no substantial modifications on the RDF (radial distribution function) for the amorphous phases have been reported for different methods of preparation or annealing conditions short of crystallization. More recently, Barna et al. [3] have found a small shift of the second peak in the RDF towards smaller r, and a more pronounced peak at 5 A for the a-Si: H prepared by glow discharge technique. These authors concluded that a higher degree of local order is present in the glow discharge a-Si: H although they stated that there exist only minor differences in amorphous silicon samples with different preparations. Earlier Raman measurements [4] have not been shown to be sensitive to preparation conditions, however, recent results indicated that Raman measurements can indeed differentiate various types of amorphous silicon samples. Tsu et al.

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.

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...

Safety considerations in using toxic and explosive gases in a production environment

This paper will detail considerations employed to insure the safe use of hazardous gases in a thin film manufacturing facility operated by Sovonics Solar Systems. The gas handling equipment will be described as well as practices and procedures that have been developed.

Development of multilayer back reflectors for improved a-Si based solar cell performance

A new back reflector comprised of an Al/(multi-layered stack)/ZnO structure is being developed to replace Al/ZnO used in manufacturing and boost conversion efficiencies with improved back reflector performance. Use of the multi-layered stack should lead to improved reflectivity that will in turn improve solar cell currents and efficiencies. Using TCOs with low indices of refraction between 1.6 and 1.7, AI(specular)/ML/ZnO back reflectors have been fabricated with reflectance values in the red portion of the light spectrum (600-1000 nm) that are close to those obtained with the AI/MgF/sub 2//Si/MgF/sub 2/ optical stacks and Ag/ZnO back reflectors. With the AI(specular)/ML/ZnO back reflector stacks, a 1.7 mA/cm/sup 2/ improvement in the red light short circuit current has been obtained for a-SiGe cells. However, the gain in red light efficiency is not as large as expected with textured back reflectors. Improvements should come through re-optimization of the multi-layer stack or use of different texturing schemes.