different light fluxes are simultaneously detectedby monitoring surface photovoltage signals atthe different modulation frequencies. Thesurface photovoltage signals are frequencycalibrated and then used to calculate a minoritycarrier diffusion length.

The performance and reliability of semicond-uctor electronic and optoelectronic devices, andthe integrated circuits that use them, depends onthe purity of the semiconductor from which thedevices are made. In particular, the level of heavymetal contaminants (e.g. Fe, Cr and other metals)which may be introduced into the semiconductorduring manufacturing and processing degradesperformance and reduces manufacturing yield.

The L-value is an indicator of semiconductormaterial purity. It gives a measure of thecontaminant concentration in the semiconductor,because heavy metals function as recombinationcentres which reduce the minority carrier lifetime.As a result, higher concentrations of contaminantsreduce the minority carrier diffusion length.Typically, the diffusion length in silicon wafers ismeasured at various stages of fabrication of micro-electronic chips to determine the concentration ofpotentially harmful impurities inadvertentlyintroduced into the wafer. Frequent monitoringof the minority carrier diffusion length helps toidentify when a given process or tool starts tocontaminate wafers above a permissible level.Preventive maintenance of processing equipmentor replacement of chemicals at this stage helps toavoid large manufacturing losses. Patent number: US 6512384 Publication date: 28 January 2003 Inventors: J. Lagowski, V. Faifer and A. Aleinikov

Thin film formation by inductivelycoupled plasma CVD process Assignees: National Institute of AdvancedIndustrial Science & Technology and AnelvaCorporation, JapanThe intention here is provide a uniform a-Si filmover a large-sized substrate at a high throughput.The chamber features an inductive couplingelectrode which has feed and grounding portionsat the two ends arranged with a high-frequencypower source and waveform generator foramplitude-modulating the power.

The inventors carried out fundamentalinvestigations on the plasma homogenizationusing the inductive coupling electrodes, andexamined several electrode structures that utilizethe standing waves that caused uniformity todeteriorate in previous inductive couplingelectrodes. By using the multi-zone film formingmethod, moreover, a higher throughput can beachieved, which contributes to further costreduction of solar cells.Patent number: US 6503816Publication date: 7 January 2003

Inventors: N. Ito, Y. Watabe, A. Matsuda andM. Kondo

Polymer-nanocrystal photo deviceand method for its productionAssignee: University of Utrecht, The NetherlandsThe method described here is claimed to be thefirst to produce operational PV cells of aconducting polymer, such as PPV, and a sinteredelectrically interconnected network ofnanocrystalline particles, such as TiO2.

The method produces a photo devicecontaining a layer of nm-sized particles and aconducting polymer in the solid state. The layer ismade by mixing the nm-sized particles in colloidwith precursor poly-paraphenylenevinylene (PPV)or a derivative thereof. The nm-sized particle isselected from TiO2, ZnO, ZrO2 or and the layeris heated to a temperature for a set period.

The invention offers a solution to the problemof creating an interpenetrating solid-stateconducting material in a nanoporous network, forthe purpose of creating stable, all-solid-statephotovoltaic cells. It avoids the instabilityproblems associated with liquid-based electrolytesin nanoporous networks.

It also offers stability, electron-transportingproperties, abundant availability, low cost and thenontoxicity of TiO2 in an interconnected networkin combination with the hole-transporting, light-absorbing, stable properties of PPV.

A further aspect of the invention is its ease ofmanufacture, in a single, combined thermaltreatment of inorganic and organic materials. Thethermal treatment is elegantly simple, andprovides for converting the polymer precursor toits final, conducting form as well as for producingelectrical contact between the inorganic nm-sizedparticles to make continuous electron-carryingpathways to the end terminal of the PV cell.Patent number: US 6512172 Publication date: 28 January 2003Inventors: J.S. Salafsky and R.E.I. Schropp

Thin-film solar cell Assignee: Sharp Corporation, JapanThis thin-film solar cell comprises a p-layer, i-layer and n-layer formed in this order as a pin-junction on a substrate in which the p-layer andi-layer are thin Si films each with a crystallinecomponent, and the p-layer contains p-typeimpurities of 0.2–8 at% and is 10–200 nm thick.

Researchers have conducted trials with respectto solar cells using thin films of crystalline silicon,i.e. polycrystalline silicon and microcrystallinesilicon. These exhibit high reliability and highphotovoltaic conversion efficiency of thecrystalline silicon solar cells as well as goodefficiency in material consumption, large areaand low costs of the amorphous silicon solar cells.

Plasma-enhanced CVD (PECVD) is onemethod of manufacturing a thin crystalline film

to be used in the solar cells. In particular, a thincrystalline silicon film is formed on a glasssubstrate by plasma-enhanced CVD at a lowtemperature not higher than 600°C. This hasdrawn attention because experience from themanufacture of the amorphous solar cells is used.

However, the photovoltaic conversionefficiency of the solar cell manufactured usingthe thin crystalline silicon film prepared in thisway is on the same level as a-Si solar cells.

The low photovoltaic conversion efficiency ofthe solar cell using the thin crystalline siliconfilm is mainly due to a low crystal fraction andan insufficient crystal orientation of the thinpolycrystalline silicon film formed on a substrateof other material than silicon.

It is known that the crystal fraction isincreased by selecting a formation temperatureor increasing the ratio of hydrogen for dilutingsilane in a reaction gas. It is also known that thecrystal orientation is improved by selecting asuitable pressure and a composition of thereaction gas or adding particular elements.

According to the invention, the crystalorientation (e.g. in the <110> direction) of the p-layer formed under the intrinsic photoelectriclayer in the solar cell is highly enhanced. As aresult, the crystal orientation (in particular <110>)of the intrinsic photoelectric conversion layerdeposited thereon is enhanced. Further, both thehigh crystal orientation and high crystal fractionare simultaneously given to the intrinsic photo-electric conversion layer, whereby a thin-film solarcell allows higher photovoltaic conversionefficiency and a method of manufacture.

The present invention also provides a methodof manufacturing the above-mentioned thin filmsolar cell, wherein the bottom layer is formed byPECVD using a very high excitation frequency.Patent number: US 6512171Publication date: 28 January 2003Inventors: T. Inamasu, M. Shimizu and K. Wada

Coated article and solar batterymoduleAssignee: TDK Corporation, JapanHere a coated article is described with a protectivemember with improved light transparency, heatand weather resistance, which is easy tomanufacture, as typified by a solar battery modulewhich experiences no performance deteriorationduring long-term outdoor installation.

To this end, this coated article has as aprotective member a silica coating obtained byapplying a polysilazane-containing coatingsolution on at least one surface of a resinoussubstrate with light transparency and heatresistance under atmospheric pressure, followedby steam oxidation and heat treatment.

The resulting organic electroluminescentdisplay is lighter in weight than conventional

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displays using glass supports and sealing glasssupports, and resistant against impact damage(e.g. panel cracking). It is therefore useful as adisplay for portable equipment.Patent number: US 6501014Publication date: 31 December 2002Inventors: Y. Kubota and M. Arai

Substrate for photoelectricconversion device, andmanufacturing methodAssignees: Nippon Sheet Glass Co Ltd, andKaneka Corporation, JapanThis patent describes a substrate for a photo-electric conversion device that is effective intrapping light in a photovoltaic layer and can bemanufactured by industrial mass-production, forwhich a method is also described.

In conventional methods for producingsubstrates for photoelectric conversion devices, asilicon oxide film with a rough surface is formedby allowing silicon oxide particles produced in thereactions to be contained in the silicon oxidecoating film, so a film formation reaction and aparticle production reaction must be controledsimultaneously. Therefore it is difficult to carryout stable manufacturing continuously.

On a glass sheet containing an alkalinecomponent, a first undercoating film containingtin oxide as a main component, a secondundercoating film, and a conductive filmcontaining tin oxide as a main component areformed in this order, thus obtaining a substrate.

The first undercoating film is formed by athermal decomposition oxidation reaction ofcoating-film forming materials containingchlorine on glass at a temperature of at least600°C. In this film, holes are formed without anaftertreatment. The surface of the conductivefilm above the holes has larger irregularities, thusscattering incident light on a photovoltaic unit.Further, a back-electrode is formed on the PVunit, to give a photoelectric conversion device.

In the new production method, it is surmisedthat sodium chloride produced in the first under-coating film by the reaction between sodium inthe glass sheet and chlorine in the material is lostfrom the film to form the holes in the firstundercoating film. Thus, a substrate suitable for athin-film photoelectric conversion device can bemanufactured by industrial mass-production.

The patent also describes a photoelectricconversion device using this substrate. At leastone photoelectric conversion unit and a back-electrode are stacked on the conductive film ofthe substrate for a photoelectric conversiondevice. The device is used with its glass sheet sidepositioned as the light-incident side.

In a-Si based thin-film photoelectric conversiondevices defect levels formed in a PV layer by lightirradiation cause deterioration in the photoelectric

conversion characteristics, so the thickness of thePV layer tends to be reduced. Therefore, in orderto compensate the decrease in light absorption, ahigher light trapping effect has been required.From such a viewpoint, the device described hereusing the new substrate is useful for improving thephotoelectric conversion characteristics comparedto a conventional device.Patent number: US 6504139Publication date: 7 January 2003Inventors: M. Hirata, T. Otani, A. Fujisawa andH. Norimatsu

Photovoltaic assembly array withcovered bases Assignee: PowerLight Corporation, USAThe invention describes an array of PVassemblies mountable on a support surface. EachPV assembly comprises a base, a PV module anda support assembly securing the module to aposition overlying the base’s upper surface.

The base comprises a main member and anelectrically conducting cover defining the base’supper surface. An electrical ground connectionmay be made between the covers of different PVassemblies. The cover may comprise sheet metal,and may have an electrically insulating surfacelayer. The main member may be a thermalinsulator, and the cover may comprise a low-emissivity layer. The covers of adjacent PVassemblies may be inter-engaged so that winduplift forces on one of the PV assemblies tend totransfer to adjacent the assemblies, to helpcounteract the wind uplift forces.

Air moving across an array of PV assembliesmounted to the roof of a building, or othersupport surface, creates wind uplift forces on thePV assemblies. Much work has been donepreviously in the design and evaluation of arraysof PV assemblies to minimize wind uplift forces.

Reducing wind uplift forces provides severaladvantages. First, it reduces the weight per arrayunit area, reducing or eliminating the need tostrengthen the support surface to support thearray’s weight, making retrofitting easier andreducing the cost. It also reduces or eliminates theneed to use roof membrane-penetrating fasteners,maintaining the membrane integrity. In addition,when designed properly, the assembly serves as aprotective layer over the roof membrane, shieldingfrom temperature extremes and UV radiation.Patent number: US 6501013Publication date: 31 December 2002Inventor: T.L. Dinwoodie

Monocrystalline powder andmonograin membrane productionAssignee: Forschungszentrum Jülich, GermanyFor production of monocrystalline powders, amelt is formed to which a fluxing agent is added.The melt contains the components of asemiconductor material, an example being the

components of copper indium diselenide, whichare generally used in a stoichiometriccomposition. The melt is usually heated totemperatures between 300 and 1000°C.

Monocrystalline powder grains grow and thedesired recrystallization takes place attemperatures above the melting points of thematerials to be fused. Once the powder grainshave the desired size, quenching stops thegrowth. The appropriate instant of quenching aswell as the appropriate temperature profile forobtaining desired powder sizes are determined by,for example, preliminary experiments. Thereafterthe fluxing agent is eliminated. Monograinmembranes are produced from the powdersproduced according to this process, and are usedin particular in solar cells. The process is simpleand inexpensive, and powder grains of uniformsize are obtained.

It is known that a monogram membrane canbe produced from monocrystalline CdS powder.Monocrystalline powder comprising CdS isobtained by crushing a relatively large singlecrystal. A bonding agent is then applied as a thinfilm on a glass substrate. The powder is scatteredon the film of the bonding agent, on which alayer of the powder adheres to the bondingagent. The other powder grains not attached tothe bonding agent are eliminated. Dissolvedresin, polymer or their components are added tothe powder grains adhering to the bondingagent. After the solution has been dried andcured, the film containing a powder layer ispeeled from the substrate. If necessary, thepowder grains can be exposed by etching,starting from the surface. Otherwise the powdergrains are or remain held together by the resinetc. and thus form the desired monogrammembrane.

One problem is the production of themonocrystalline powder. For example, it isrelatively expensive to produce a large singlecrystal. It is also hardly possible to producepowder grains of uniform size by mechanicalcrushing. Powder grains of uniform size arenecessary to obtain a monogram membrane ofuniform thickness. A monogram membrane canbe used advantageously in photovoltaics, amongothers. Copper indium diselenide is aparticularly suitable material for this purpose.

The object of the invention is to provide aninexpensive process for production ofmonocrystalline powder with predeterminedgrain sizes. A further object is to provide, for thefirst time, particular monogram membranescomprising powders formed according to theprocess.Patent number: US 6488770Publication date: 3 December 2002Inventors: D. Meissner, E. Mellikov and M.Altosaar

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