摘要:

A comprehensive study of hydrogenated amorphous silicon (a‐Si:H) deposited by hot wire and conventional glow discharge suggests that temperatures above the so called optimum 250 °C substrate temperature can produce device‐quality films. These films show enhanced transport properties and improved structural order. In addition we show that hot wire material can be produced with just as many hydrogen atoms as are needed to passivate most of the dangling bonds present in unhydrogenateda‐Si:H.

ISSN:0094-243X    

DOI:10.1063/1.42945

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Cadmium sulfide (CdS), grown from an aqueous solution, and zinc oxide (ZnO), cadmium zinc sulfide (Cd1−xZnxS), and zinc selenide (ZnSe), deposited by metalorganic chemical vapor deposition (MOCVD), have been used as the window for thin film cadmium telluride (CdTe) solar cells. Thin film solar cells were prepared by the successive deposition of the window andp‐CdTe (by MOCVD and close‐spaced sublimation, CSS) on SnO2:F/glass substrates. CdS/CdTe(CSS) solar cells show considerably better characteristics than CdS/CdTe(MOCVD) solar cells because of the better microstructure of CSS CdTe films. Total area conversion efficiency of 14.6%, verified by the National Renewable Energy Laboratory, has been achieved for solar cells of about 1 cm2area. Solar cell prepared by using ZnO, ZnSe, or Cd1−xZnxS as window have significantly lower photovoltage than CdS/CdTe solar cells.

ISSN:0094-243X    

DOI:10.1063/1.42946

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

A diode array fabrication process is described that produces edge‐passivated devices of extremely low leakage currents. These small‐area mesa diodes can be probed to determine the spatial variations in the cell and the material parameters. The measurements that can be routinely performed on these devices include dark and illuminated current‐voltage (I‐V) characteristics, optical and electron beam scanning, minority carrier lifetime, capacitance‐voltage (C‐V) measurements for resistivity, and impurity analysis by deep level transient spectroscopy (DLTS). Consequently, the cell parameters can be correlated with the substrate parameters. The information acquired via this technique is required to improve material growth, design optimum cell fabrication processes, and predict large‐area cell performance intrinsically controlled by the substrate.

ISSN:0094-243X    

DOI:10.1063/1.42948

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

This paper describes recent results of the numerical simulation of CuInSe2solar cells. A ZnO/CdS/CIS solar cell, for which an experimental illuminated current‐voltage characteristic and a quantum efficiency measurement were available in the literature, was simulated. Using material parameters available in the literature and adjusting the CIS lifetime as well as the thickness of a hypothetical Cu‐poor CIS layer, excellent agreement with experiment was obtained. It should be noted that this is not necessarily a unique representation of the device. The effects of the Cu‐poor layer thickness on cell performance was then examined. It is shown that thin Cu‐poor layers lead to cells with a relatively highVOC, but a relatively lowJSC. Thick Cu‐poor layers lead to cells with a relatively lowVOC, but a relatively highJSC. It is suggested that control of the Cu‐poor layer thickness can lead to a higher efficiency CIS solar cell.

ISSN:0094-243X    

DOI:10.1063/1.42925

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Selenization is the current process by which state‐of‐the‐art CuInSe2polycrystalline thin‐film photovoltaic modules are industrially fabricated. The distinguishing characteristic of this approach is that material deposition is separate from compound formation. In conventional selenization, In‐Cu layers, often referred to as precursors, are deposited on molybdenum‐coated glass substrates and subsequently transformed into CuInSe2following exposure to a selenium‐containing environment. Although the highly toxic gas, H2Se, has been considered a necessary component of selenization, recent safety concerns have accelerated the development of Se vapor as a possible substitute for H2Se. In more recent variations of the process, solid selenium is incorporated during the precursor fabrication step, and subsequent thermal annealing is used to form compounds among the three elements. In this paper, we discuss the thermodynamic fundamentals of selenization using elemental Se as an alternative to H2Se. This discussion is augmented by empirical observations drawn from our own efforts in fabricating efficient (≳10%) CdS/CuInSe2devices by selenization in thermally‐evaporated Se vapors. Indium transport, presumably via the formation of In2Se or InSe gaseous species, dominates the kinetics of selenization using sequentially evaporated (indium on copper) precursors, while lateral phase separation was observed in the case of co‐deposited In+Cu precursors.

ISSN:0094-243X    

DOI:10.1063/1.42926

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Low‐temperature photoluminescence, photoluminescence excitation, and photoreflectance modulation measurements are used to probe the electronic structure and the dielectric function of (001) (GaP)2/(InP)2superlattices (grown on a GaInP2buffer) that exhibit lateral composition modulation. An 8×8 Luttinger‐model Hamiltonian, which includes the effects of coherency strain generated by the lateral composition modulation, is used to analyze the experimental results. These studies yield the first experimental evidence for a spontaneously generated effective mass superlattice.

ISSN:0094-243X    

DOI:10.1063/1.42927

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

Under certain growth conditions, the single‐crystal alloy Ga0.5In0.5P spontaneously orders on the group III sublattice with gallium and indium atoms occupying alternating (111) planes. The ordered structure has been associated with variations in the observed band gap, extra and moving optical transitions, anomalous polarization effects, and very long low‐temperature photoluminescence lifetimes. The observed variations may be attributed to ordering or potential fluctuations associated with imperfect and nonuniform ordering and are a complex function of the growth parameters. Such anomalous optical properties may also be observed in other alloys that exhibit potential fluctuations, e.g., amorphous silicon and CuInSe2.

ISSN:0094-243X    

DOI:10.1063/1.42928

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We review our recent high‐depth‐resolution secondary ion mass spectrometry studies of hydrogen diffusion in amorphous silicon. We describe the trap‐controlled H diffusion model supported by the experiments. Recent results on light enhancement of H diffusion ina‐Si:H are also discussed.

ISSN:0094-243X    

DOI:10.1063/1.42929

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

We have investigated the properties of individual grains in polycrystalline thin films of CuInSe2and CdTe by transmission electron microscopy (TEM), transmission electron diffraction (TED), scanning electron microscopy (SEM), and energy dispersive x‐ray spectroscopy (EDS) in a Scanning Transmission Microscope (STEM). TED experiments showed that most grains possess the chalcopyrite structure, which is expected for CuInSe2. In some cases, however, a complex arrangement of different phases was found within a single grain, allowing a glimpse at the kinetics of the grain boundaries, EDS spectra were recorded in a SEM. The spectra show unambiguously the presence of grains with disparate composition. To assess the compositional changes within single grains, EDS spectra were taken at various locations on the grains in a STEM. Using the total photon count as a measure of the local grain thickness and the ratio of SeK&agr;/SeL&agr;intensities to correct for absorption losses, we can analyze the relative concentrations of Se, In, and Cu independently of grain thickness. CdTe films, grown on a CdS/SnO2/glass and examined by SEM showed that the grain size depends primarily on the film thickness. TEM experiments revealed the type, density, and distribution of the structural defects in this material. Threading dislocations, stacking faults, and twinned grains were frequently observed. However, their densities differed markedly from one grain to the next. Some grains exhibited defect densities in excess of 109cm−2, while adjacent grains were virtually defect free. Cathodoluminescence experiments in the SEM showed a similar difference in the density of nonradiative recombination centers. The grain boundaries were found to be sites of enhanced nonradiative recombination.

ISSN:0094-243X    

DOI:10.1063/1.42906

出版商:AIP    

年代:1992

数据来源: AIP

摘要:

The minority‐carrier lifetime of polycrystalline CdTe has been measured for a variety of samples produced by two different growth techniques. The CdS/CdTe solar cell structures were either grown by a proprietary spray technique at Photon Energy, Inc. or by close‐spaced sublimation at the University of South Florida. The photoluminescence decay lifetime is investigated as a function of grain size, excess carrier density, and temperature. Results are consistent with carrier recombination at grain boundaries, indicate some defects act as traps, and show relatively high efficiency solar cells can be made from material exhibiting sub‐nanosecond lifetimes.

ISSN:0094-243X    

DOI:10.1063/1.42907

出版商:AIP    

年代:1992

数据来源: AIP