David H. Ford

Serotonergic component of SCH 23390: in vitro and in vivo binding analyses

A series of benzazepines related to SCH 23390 were tested for binding to the 5HT-2 receptor. The compounds tested inhibited the binding of 3H-ketanserin with KI values generally greater than those observed for the D-1 receptor, but less than those for the D-2 receptor. When this serotonergic activity was correlated to the D-1 activity, the resulting coefficient was 0.84, indicating a strong correlation between the two activities. Conversely, the 5HT-2 activity did not show a good correlation with the D-2 activity. To further test the significance of the 5HT-2 binding of the SCH 23390, in vivo binding studies were performed using 125I-SCH 38840 in the frontal cortex, an area containing both D-1 and 5HT-2 receptors. The in vivo binding of 125I-SCH 38840 to frontal cortex exhibited peak levels one hour following subcutaneous administration, similar to the time course previously observed in striatum. The binding was both D-1 and tissue specific. Competition studies with selected standards demonstrated that inhibition of the binding to frontal cortex, in contrast to the inhibition observed in the striatum, exhibited a Hill coefficient less than unity, implying interaction at more than one receptor subtype. When SCH 23390 and ketanserin were administered simultaneously, the inhibition of the in vivo binding of 125I-SCH 38840 to striatum was not different than that observed with SCH 23390, alone. However, the inhibition of binding to frontal cortex was significantly greater than that demonstrated with either SCH 23390 or ketanserin, alone, suggesting that 125I-SCH 38840 was binding to both D-1 and 5HT-2 receptors, in vivo.

High current, thin silicon-on-ceramic solar cell

Thin-film polycrystalline silicon solar cells offer the potential to achieve 19% efficient photovoltaic power conversion. Well-designed, 20-100 micron thick, thin-film silicon solar cells can achieve high efficiency by employing light trapping and back surface passivation. Low cost is achieved by minimizing the amount of feedstock silicon required per watt of power output. Electrically insulating supporting substrates enable monolithic, series-connected submodules. A solar cell device comprised of a 20 micron thick layer of silicon grown on an insulating ceramic substrate, designed to effect light-trapping and back surface passivation, has resulted in an independently verified short circuit current of 25.8 mA/cm/sup 2/. Analysis of the spectral response of the solar cell indicates the presence of both light-trapping and back surface passivation with an effective diffusion length in excess of twice the device thickness.

Development of light-trapped, interconnected, Silicon-Film modules

AstroPower is employing Silicon-Film/sup TM/ technology toward the development of an advanced thin-silicon-based, photovoltaic module product. This module combines the design and process features of advanced thin-silicon solar cells, is light trapped, and integrated in a low-cost monolithic interconnected array. This advanced product includes the following features: (a) silicon layer grown on a low-cost substrate; (b) a nominally 50-micron thick silicon layer with minority carrier diffusion lengths exceeding 100 microns; (c) light trapping due to back-surface reflection; and (d) back surface passivation. The thin silicon layer achieves high solar cell performance and can lead to a module conversion efficiency as high as 19%. These performance design features, combined with low-cost manufacturing using relatively low-cost capital equipment, continuous processing and a low-cost substrate, will lead to high performance, low cost photovoltaic panels.

Thin film polycrystalline silicon solar cells

Abstract A thin crystalline silicon solar cell with low back surface recombination will exhibit slightly higher efficiency than a thick silicon solar cell having similar material quality. When light trapping is added to the thin silicon solar cell, the efficiency can improve by as much as 20%. Following a summary of historical results, the predictions of the model are described including the preferred geometrical structures for light trapping. Recent experimental results are reported. The thin, light trapping technology can be extended to a monolithic interconnected device.

13% Silicon Film/sup TM/ solar cells on low-cost barrier-coated substrates

Thin-film polycrystalline silicon solar cells offer significant cost savings over single crystal and cast polycrystalline wafers that are sliced from ingots, and they are more stable than amorphous silicon solar cells which suffer from photo-induced degradation. A new barrier layer and low cost substrate that meet the criteria for thin films of polycrystalline silicon to be grown using the Silicon Film/sup TM/ process has been developed. Films grown on this new barrier/substrate combination have exhibited minority carrier diffusion lengths as high as 250 /spl mu/m when external phosphorous gettering is employed. Using conventional silicon processing technologies, with special provision made for electrical connection to the base layer, an efficiency of 13.8% has been measured in a 0.46 cm/sup 2/ thin-film polycrystalline silicon solar cell grown on this new barrier-coated substrate. Technical details of the development are presented in this paper.

Development of large area thin crystalline silicon-film solar cells

The development of thin polycrystalline silicon-film solar cells on low-cost ceramic substrates for commercial power applications is presented. The silicon-film solar cell design uses light trapping to achieve increases in voltage, current, and efficiency compared to conventional thick polycrystalline solar cells. The device analysis indicates that a solar cell conversion efficiency of 19% is achievable using thin (30 mu m) polycrystalline silicon-film designs. This performance prediction exceeds that of the conventional thick (400 mu m) polycrystalline silicon solar cell. 1 cm/sup 2/, 14.2% laboratory-scale and a 78 cm/sup 2/, 8.5% commercial size solar cell are demonstrated.<<ETX>>

High power, commercial Silicon-Film/sup TM/ solar cells

Silicon-Film/sup TM/ wafers are cut from continuous sheets of solar cell quality silicon grown on low cost substrates. The original Silicon-Film/sup TM/ solar cells, the AP-225, were squares cut 15.4 cm on a side for an area of 236 cm/sup 2/. The 15.4 cm dimension was the largest width that could be cut from the sheet while maintaining reasonable uniformity. Improvements in process control provided the opportunity to cut wafers that are 17.8 cm on a side for an area of 316 cm/sup 2/. This larger area has led to a new solar cell, the AP-300, with a power of 3.5 W. This power is the highest available for any commercial polycrystalline silicon solar cell. Increased power, while maintaining the cost of handling a single unit, results in enhanced value in the final product. A unique gettering process that utilizes a front surface aluminum layer has been developed to enhance solar cell performance. Prior to the work presented here, this process had achieved a 2.82 W solar cell for an area of 239 cm/sup 2/. Present process development and optimization efforts are concentrated on fine-tuning the silicon growth process and improving post-growth processing techniques. Post-growth improvement of minority carrier lifetime is accomplished through external gettering and bulk defect passivation techniques. This paper presents the solar cell process development that led to the demonstration of a 3.5 W large area AP-300 solar cell.

Large-area Silicon-Film™ manufacturing

The Silicon-Film™ process is on an accelerated path to large-scale manufacturing. A key element in that development is optimizing the specific geometry of both the Silicon-Film™ sheet and the resulting solar cell. That decision has been influenced by cost factors, engineering concerns, and marketing issues. The geometry investigation has focused first on sheet nominally 15 cm wide. This sheet generated solar cells with areas of 240 cm2 and 675 cm2. Most recently a new sheet fabrication machine was constructed that produces Silicon-Film™ with a width in excess of 30 cm. The results of testing have indicated that there is no limit to the width of sheet generated by this process. The new wide material has led to prototype solar cells with areas of 300, 400 and 1800 cm2. Test results are available on some sizes, with all results expected later this year. Significant advances in solar cell processing have been developed in support of fabricating devices of this size including diffusion and application of the a...

Light-trapping and back surface structures for polycrystalline silicon solar cells

Light-trapping in polycrystalline silicon solar cells is usually considered to be more difficult to implement than that in single crystal silicon solar cells due to the random crystallographic orientations in various grains. Furthermore, if minority carrier diffusion length is on the order of or less than solar cell thickness, which is the case of most cost-effective polycrystalline silicon, the translation of optical gain, achieved from light-trapping, into electrical gain will be rather limited, even with a perfect back surface passivation. In this work, geometrical light-trapping structures are demonstrated using a simplified isotropic etching at polycrystalline silicon surfaces. Combined with a back surface reflector (BSR), an enhanced absorption in the long wavelength region is measured with a low parasitic absorption. Different light-trapping structures are experimentally compared. To further examine the electrical gain from light-trapping, a three-terminal solar cell structure is used. This structure allows three different back surface configurations to be realized in a single device: unpassivated, passivated with a floating junction, and enhanced with a collecting junction. Results indicate that even with a relatively short minority-carrier diffusion length the current collection in the long wavelength region can be significantly improved and the light-trapping effect is enhanced as well. Copyright

16.6% efficient Silicon-Film/sup TM/ polycrystalline silicon solar cells

A 16.6% efficient Silicon-Film/sup TM/ solar cell has been demonstrated and verified on a one-square-centimeter device. This result was achieved with an improved blue response using an optimized low-temperature PECVD oxide passivation and reduced optical losses by the reduction of grid obscuration and front reflectance. Ongoing efforts have been centered on the material growth to better control grown-in impurities and defects, post-growth material enhancements to effectively remove impurities and passivate bulk defects, and device optimisations to further reduce device optical and electrical losses. Model calculations indicate that an efficiency over 18% is achievable if further optimizations in antireflection coating and improvements in minority carrier diffusion length can be effected.