摘要:

This paper discusses applications of the tight‐binding method to: i) localized anti‐bonding states of Si‐H groups ina‐Si:H, and ii) dangling bond defect states ina‐Si,Ge:H alloys. Thea‐Si:H calculations demonstrate that anti‐bonding states of Si‐H groups with bond‐angle distortions of ∼16°–20° or more can be localized below the conduction band edge, and display the trapping properties of floating‐bond defect states. The calculations for thea‐Si,Ge:H alloys show that the average‐alloy bond‐angle disorder, ∼6–8°, can induce a spread in the energies of Si and Ge dangling bond states of ∼0.3 eV, that is larger than that due to chemically‐induced splittings, 0.11–0.15 eV, which include the effects of different distributions of nearest‐neighbor Si and/or Ge‐atoms. The bond‐angle disorder induced dispersion leads to a spectral overlap of the Ge and Si dangling bonds, so that both types of defects can be observed in alloy samples.

ISSN:0094-243X    

DOI:10.1063/1.42891

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Zinc oxide and tin oxide films have been deposited by atmospheric pressure chemical vapor deposition. Zinc oxide films doped with fluorine have higher mobility and higher visible transmission than those doped with the Group III elements (B, Al, Ga). A ZnO:F film with a sheet resistance of 5 &OHgr;/square has an average visible absorption of about 3%. Various doped zinc oxide films were compared with each other and with SnO2:F films through their Figure of Merit, which is defined as the ratio of the conductivity over the visible absorption coefficient. Zinc oxide films doped with fluorine have the highest Figure of Merit and are very promising as transparent electrodes for solar cells with high cell efficiency.

ISSN:0094-243X    

DOI:10.1063/1.42892

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We describe a new technique, Reactive Plasma Beam Deposition, for growinga‐Silicon films at higher temperatures. The technique uses a reactive beam of H atoms and ions, produced using an Electron Cyclotron Resonance (ECR) plasma source, to decompose SiH4and deposit films and devices. We find that the quality of the films depends critically upon the flux of H radicals reaching the substrate. Control over this flux by allows us to grow high quality films even at temperatures of 400–450C. We find that these films are more stable than comparable quality films deposited by glow discharge at lower temperatures, presumably due to a better local microstructure created by higher growth temperatures. The films have very good electronic properties. We have also made preliminaryp‐i‐nsuperstrate devices in these materials. The quantum efficiency data indicate that the hole mu‐Tau products in these materials are quite good, 3–4×10−8cm2/sec.

ISSN:0094-243X    

DOI:10.1063/1.42893

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Large batches of nominal 10 cm×10 cm solar cells of 14% efficiency have been made from improved lifetime silicon sheet octagons grown by the Edge‐defined Film‐fed Growth (EFG) technique. At the level of bulk material quality achieved, limitations to further increases in cell efficiencies start to arise from solar cell design. The potential is examined for producing over 16% cell efficiencies with current EFG octagon material as its thickness is decreased from 400 to 200 &mgr;m.

ISSN:0094-243X    

DOI:10.1063/1.42894

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The paper will review what is presently known about the properties of vacancies and self‐interstitials such as their thermal equilibrium concentrations and diffusivities. We will also report on recent measurements of grown‐in vacancy concentrations by a method using platinum decoration of vacancies.

ISSN:0094-243X    

DOI:10.1063/1.42897

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Secondary ion mass spectrometry (SIMS) is used to study the gettering of chromium from silicon during solid source phosphorus diffusion. Low dose ion implants are used to introduce chromium into the silicon. SIMS depth profiles from the as‐implanted and the phosphorus‐diffused materials show that the majority of chromium is removed from the silicon during the diffusion of phosphorus to form thep‐njunction. Annealing times of 1 and 5 minutes are shown to be as effective as annealing times of 30 minutes for the removal of the implanted Cr.

ISSN:0094-243X    

DOI:10.1063/1.42898

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A combination of theoretical modelling, gettering and passivation, and cell fabrication is presented in this paper to provide guidelines for improving efficiency of polycrystalline solar cells. Theoretical modelling was performed to show that grain boundary barrier height decreases and carrier diffusion length increases with illumination level (≤50 suns) in those polycrystalline materials where grain boundary dominates the recombination. Model calculations show that the efficiency spread due to grain boundary defect density (Nst) in the range of 1011–1012cm−2in 1 mm grain size polysilicon cells at one sun can be virtually eliminated at 50 suns due to higher relative enhancement in diffusion length in the cells with highNst. Thus higher illumination level behaves similar to grain boundary passivation. Phosphorous and aluminum treatments were investigated and optimized for gettering and passivation. A deep phosphorous diffusion on the front, followed by a partial etch back, and 850 °C aluminum treatment on the back gave record high 17.7% efficient one sun solar cells on Osaka Titanium Corporation (OTC) polycrystalline silicon.

ISSN:0094-243X    

DOI:10.1063/1.42949

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A porous silicon (PS) layer can be produced on a crystalline silicon substrate by electrochemical or chemical etching in hydrofluoric acid (HF) solutions. There are many properties that make PS thin films interesting for photovoltaic applications, such as a possible direct band gap that can be adjusted between 1.5 and 1.9 eV, textured surfaces for light trapping, the potential for low cost and large‐area fabrication, and the possibility of tandem cell structures with Si. We report the fabrication of large area PS (up to 3‘diameter) with quite uniform photoluminescence (PL) properties, and studies of the effects of post‐hydrogenation treatments on the intensity and stability of the PL from PS. We have observed that a remote‐plasma processing treatment can increase the PL emission intensity from PS prepared under certain conditions by 100 times or more. The emission band is narrower and centered more toward the blue for the remote‐plasma processed sample, and the PL emission intensity does not degrade in an air ambient over a period of at least several weeks. This result indicates that PS has the potential to become a stable and useful optoelectronic material.

ISSN:0094-243X    

DOI:10.1063/1.42899

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Testing thin‐film modules significantly contributes to the understanding of field performance and the reliability of emerging PV technologies. A number of programs are under way at NREL for testing flat‐plate PV modules and monitoring their performance in sunlight and under simulated conditions to provide accelerated performance characteristics that represent long‐term exposure to normal weather conditions. Modules are installed outdoors and connected to loads, and their performance is monitored. Other modules are mounted in environmental chambers and are exposed to the rigors of heating, freezing, and high humidity. Modules are exposed to simulated rain and are tested for electrical leakage and are also exposed to simulated hail stones to determine structural integrity. Performance tests are conducted under standard test conditions (STC) in accordance with ASTM E1036. This paper presents some of the details of PV module testing at NREL.

ISSN:0094-243X    

DOI:10.1063/1.42900

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Yellow‐browning of the ethylene‐vinyl acetate (EVA) copolymer encapsulant used in PV modules has resulted in significant power losses of over 50% of the initial power output. The weathering‐degraded yellow‐brown EVA films have lost the ultraviolet (UV) absorber, Cyasorb UV 531(R), and the degree of cross‐linking (gel content) has increased. EVA degradation mechanisms identified thus far are discussed in this work. Upon exposure to UV light at 45°–85 °C, virgin EVA films that are stabilized with Cyasorb UV 531(R)and two antioxidants show an increase in the gel content, a gradual loss of Cyasorb by photooxidation, and the generation of acetic acid. The deacetylation reaction, which leads to the formation of polyenes, also occurs significantly in the films heated in the dark at 130 °C for five days. Acetic acid thermally catalyzes the EVA film discoloration at 85°–130 °C, which increases from a light yellow to a yellow‐brown color as the heating temperature increases. The factors can account for the yellow‐browning of the EVA in the accelerated testing of mini‐modules, and the discoloration is more profound when exposed to UV light at 85 °C than when heated in the dark at the same temperature. In the presence of the EVA‐produced acetic acid, oxygen, and sunlight exposure, the Cu buslines that were coated with a thin layer of Pb‐Sn alloy showed significant oxidation and metal interdiffusion, which in turn may contribute to the resistance increase and hence the current loss reported for weathered PV modules.

ISSN:0094-243X    

DOI:10.1063/1.42901

出版商:AIP    

年代:1992

数据来源: AIP