Process Research on Polycrystalline Silicon Material (PROPSM)

Results of hydrogen-passivated polycrystalline silicon solar cells are summarized. Very small grain or short minority-carrier diffusion length silicon was used. Hydrogenated solar cells fabricated from this material appear to have effective minority-carrier diffusion lengths that are still not very long, as shown by the open-circuit voltages of passivated cells that are still significantly less than those of single-crystal solar cells. The short-circuit current of solar cells fabricated from large-grain cast polycrystalline silicon is nearly equivalent to that of single-crystal cells, which indicates long bulk minority-carrier diffusion length. However, the open-circuit voltage, which is sensitive to grain boundary recombination, is sometimes 20 to 40 mV less. The goal was to minimize variations in open-circuit voltage and fill-factor caused by defects by passivating these defects using a hydrogenation process. Treatments with molecular hydrogen showed no effect on large-grain cast polycrystaline silicon solar cells

Process Research on Polycrystalline Silicon Material (PROPSM)

Results of hydrogen-passivated polycrysalline silicon solar cell research are summarized. The short-circuit current of solar cells fabricated from large-grain cast polycrystalline silicon is nearly equivalent to that of single-crystal cells, which indicates long bulk minority-carrier diffusion length. Treatments with molecular hydrogen showed no effect on large-grain cast polycrystalline silicon solar cells

Silicon-on-ceramic process: Silicon sheet growth and device development for the large-area silicon sheet task of the low-cost solar array project

The technical feasibility of producing solar cell quality sheet silicon to meet the DOE 1986 cost goal of 70 cents/watt was investigated. The silicon on ceramic approach is to coat a low cost ceramic substrate with large grain polycrystalline silicon by unidirectional solidification of molten silicon. Results and accomplishments are summarized

Development of high efficiency solar cells on silicon web

Web base material is being improved with a goal toward obtaining solar cell efficiencies in excess of 18% (AM1). Carrier loss mechanisms in web silicon was investigated, techniques were developed to reduce carrier recombination in the web, and web cells were fabricated using effective surface passivation. The effect of stress on web cell performance was also investigated

Scanning mid-IR-laser microscopy: an efficient tool for materials studies in silicon-based photonics and photovoltaics

A method of scanning mid-IR-laser microscopy has recently been proposed for the investigation of large-scale electrically and recombination-active defects in semiconductors and non-destructive inspection of semiconductor materials and structures in the industries of microelectronics and photovoltaics. The basis for this development was laid with a wide cycle of investigations on low-angle mid-IR-light scattering in semiconductors. The essence of the technical idea was to apply the dark-field method for spatial filtering of the scattered light in the scanning mid-IR-laser microscope together with the local photoexcitation of excess carriers within a small domain in a studied sample, thus forming an artificial source of scattering of the probe IR light for the recombination contrast imaging of defects. The current paper presents three contrasting examples of application of the above technique for defect visualization in silicon-based materials designed for photovoltaics and photonics which demonstrate that this technique might be an efficient tool for both defect investigation and industrial testing of semiconducting materials.Comment: DRIP-

Task-Based Information Compression for Multi-Agent Communication Problems with Channel Rate Constraints

A collaborative task is assigned to a multiagent system (MAS) in which agents are allowed to communicate. The MAS runs over an underlying Markov decision process and its task is to maximize the averaged sum of discounted one-stage rewards. Although knowing the global state of the environment is necessary for the optimal action selection of the MAS, agents are limited to individual observations. The inter-agent communication can tackle the issue of local observability, however, the limited rate of the inter-agent communication prevents the agent from acquiring the precise global state information. To overcome this challenge, agents need to communicate their observations in a compact way such that the MAS compromises the minimum possible sum of rewards. We show that this problem is equivalent to a form of rate-distortion problem which we call the task-based information compression. We introduce a scheme for task-based information compression titled State aggregation for information compression (SAIC), for which a state aggregation algorithm is analytically designed. The SAIC is shown to be capable of achieving near-optimal performance in terms of the achieved sum of discounted rewards. The proposed algorithm is applied to a rendezvous problem and its performance is compared with several benchmarks. Numerical experiments confirm the superiority of the proposed algorithm.Comment: 13 pages, 9 figure

Silicon-on ceramic process: Silicon sheet growth and device development for the large-area silicon sheet task of the low-cost solar array project

The technical feasibility of producing solar-cell-quality sheet silicon to meet the Department of Energy (DOE) 1986 overall price goal of $0.70/watt was investigated. With the silicon-on-ceramic (SOC) approach, a low-cost ceramic substrate is coated with large-grain polycrystalline silicon by unidirectional solidification of molten silicon. This effort was divided into several areas of investigation in order to most efficiently meet the goals of the program. These areas include: (1) dip-coating; (2) continuous coating designated SCIM-coating, and acronym for Silicon Coating by an Inverted Meniscus (SCIM); (3) material characterization; (4) cell fabrication and evaluation; and (5) theoretical analysis. Both coating approaches were successful in producing thin layers of large grain, solar-cell-quality silicon. The dip-coating approach was initially investigated and considerable effort was given to this technique. The SCIM technique was adopted because of its scale-up potential and its capability to produce more conventiently large areas of SOC

Local optical and electrical characteristics of optoelectronic devices

Konverze solární energie a miniaturizace polovodičových součástek a s tím spojená životnost, spolehlivost a účinnost zařízení jsou základní premisy této práce. Práce je zaměřena na studium a nedestruktivní diagnostiku optoelektronických součástek, především solárních článků. Ty jsou výhodné pro studium především proto, že mají přístupný pn přechod blízko povrchu a obsahují značné množství nehomogenit. Vzhledem k rozměrům nehomogenit bylo ještě donedávna obtížné zkoumat jejich lokální fyzikální (tj. elektrické a optické) charakteristiky, které by umožnily lépe pochopit jejich chování. Vybudování vlastního měřicí pracoviště, které splňuje specifické požadavky pro oblast měření lokálního optického vyzařování a lokálně indukovaného proudu, umožnilo dosáhnout lokalizaci a detekci nehomogenit s rozlišením přibližně 100 nm. Jádrem práce je charakterizace nedokonalostí s využitím nedestruktivních technik, a to nejen z makroskopického hlediska, ale především v mikroskopickém měřítku s využitím sondové mikroskopie. Nedílnou součást práce tedy tvoří studium problematiky charakterizačních technik pro optoelektronické součástky, studium mikroskopických technik, především sondových a problematika zpracování naměřených dat. Pro účely mikroskopické charakterizace je použit mikroskop se skenující sondou v blízkém optickém poli, který kromě morfologie povrchu umožňuje zkoumat také lokální optické, optoelektrické a elektrooptické vlastnosti struktur ve vysokém prostorovém rozlišení. Z makroskopického hlediska jsou v rámci práce zkoumány vzorky s využitím techniky lokálně indukovaného proudu, voltampérových charakteristik vzorků, emise ze závěrně polarizovaných vzorků ale i jejich teplotních závislostí. Společným využitím těchto technik je možné lokalizovat defekty a nehomogenity struktury, které byly následně podrobeny kompozitní analýze a dále zobrazeny s využitím elektronové mikroskopie. Mezi konkrétní výstupy práce patří specifikace možností využití nedestruktivních charakterizačních technik pro studium optoelektronických součástek a zvláště pak pro klasifikaci jejich defektů. Dále jsou formou metodiky popsány experimentální charakterizační techniky a postupy charakterizace defektů. Klíčovým výstupem je katalog objevených typů defektů, ve kterém jsou ukázány konkrétní defekty vzorků a jejich lokální vlastnosti v mikroskopickém měřítku společně s popisem jejich vlivu na celý vzorek.Solar energy conversion, miniaturization of semiconductor devices and associated lifetime, reliability and efficiency of devices are the basic premise of this work. This work is focused on the study of optoelectronic devices especially solar cells and its nondestructive diagnostic. Solar cells are advantageous for study mainly because the pn junction is located near the surface and contains a lot of inhomogeneities. It has been difficult until recently to investigate their local physical (electrical and optical) parameters due to the size of inhomogeneities. Behavior of inhomogeneities can be well understood with knowledge of its local properties. Establishment of measurement workplace, that satisfies requirements for measurement of local emission and optically induced current measurement, allows us detection and localization of inhomogeneities with spatial resolution more or less 100 nm. The core of thesis is characterization of imperfection using nondestructive techniques in the macroscopic region but primarily in microscopic region using scanning probe microscopy. Integral parts of the work are characterization techniques for photoelectrical devices, microscopic techniques and data processing. Scanning near-field optical microscope is used for the purpose of microscopic characterization such as topography, local optical, photoelectrical and electrooptical properties of structures in high spatial resolution. Locally induced current technique, current voltage characteristics, emission from reversed bias pn junction measurement including its thermal dependence are used for samples investigation in macroscopical region. It is possible to localize defects and structure inhomogeneity using mentioned techniques. Localised defects are consequently analyzed for composition and measured using electron microscopy. Specific outputs of work are classification of photoelectric devices defects and specification of nondestructive characterization techniques used for defect detection. Experimental characterization techniques are described together with defects measurement procedures. The key output is the catalog of serious defects which was detected. Particular defects of samples are shown including describe of its properties and physical meaning.

Dip-coating process: Silicon sheet growth development for the large-area silicon sheet task of the low-cost silicon solar array project

The objective of this research program is to investigate the technical and economic feasibility of producing solar-cell-quality sheet silicon by coating one surface of carbonized ceramic substrates with a thin layer of large-grain polycrystalline silicon from the melt. The past quarter demonstrated significant progress in several areas. Seeded growth of silicon-on-ceramic (SOC) with an EFG ribbon seed was demonstrated. Different types of mullite were successfully coated with silicon. A new method of deriving minority carrier diffusion length, L sub n from spectral response measurements was evaluated. ECOMOD cost projections were found to be in good agreement with the interim SAMIS method proposed by JPL. On the less positive side, there was a decrease in cell performance which we believe to be due to an unidentified source of impurities