Search

The protection of intellectual property rights concerns companies in virtually every industry. Moreover, internationalization of the marketplace has caused the issues of intellectual property protection and international trade to become [...]

Silicon nanocrystals are a promising candidate materials system for active devices such as modulators, optical amplifiers, and light-emitting diodes (see 'Nanocrystals: quantum-mechanical optical materials' p. 79). Luminescence in nanocrystals is [...]

We demonstrate a novel concept for III-V engineered substrate cost reduction that does not rely on chemical–mechanical polishing or low-throughput release layer etching. With the potential for significant reduction to III-V substrate cost, the details of this concept are provided, as well as a demonstration of III-V devices grown on a membrane removed from its source substrate and bonded to a non-native target handle. The GaAs solar cell on membrane one-sun and concentration AM1.5 efficiencies register 16.2% and 19.1%, respectively, prior to the application of anti-reflection coating. This is a discrepancy of 2% (one-sun) and 1.2% (concentration) absolute versus a nominally identical control GaAs device, indicating the capability for high performance at reduced cost.

This article illustrates the importance of gathering and analyzing preprocessing data for unlisted but rich firms such as venture capital firms. Using datasets from three major sources, the authors demonstrate how to query and analyze data using both Datastream and SQL.

Quaternary alloys are essential for the development of high-performance optoelectronic devices. However, immiscibility of the constituent elements can make these materials vulnerable to phase segregation, which degrades the optical and electrical properties of the solid. High-efficiency III–V photovoltaic cells are particularly sensitive to this degradation. InAlAsSb lattice matched to InP is a promising candidate material for high-bandgap subcells of a multijunction photovoltaic device. However, previous studies of this material have identified characteristic signatures of compositional variation, including anomalous low-energy photoluminescence. In this work, atomic-scale clustering is observed in InAlAsSb viaquantitative scanning transmission electron microscopy. Image quantification of atomic column intensity ratios enables the comparison with simulated images, confirming the presence of nonrandom compositional variation in this multispecies alloy.

Increasing epitaxial growth rate is an important path toward III-V solar cell cost reductions; however, photovoltaic device performance has been shown to degrade with increasing growth rate. In this study, gallium arsenide (GaAs) material has been deposited via metal-organic chemical vapor deposition (MOCVD) at growth rates varying between 14 and 60 μm/h. Deep-level transient spectroscopy is utilized to elucidate an exponential rise in EL2 trap density as a function of growth rate when all other growth conditions are held constant. Evidence is provided that this EL2 defect is responsible for limiting the Shockley-Read-Hall (SRH) lifetime of very high growth rate solar cells. The effect of growth temperature on devices at high growth rate is subsequently investigated as a strategy to reduce trap density and improve solar cell performance. From this investigation, EL2 trap density is suppressed, and single-junction on-substrate GaAs solar cells grown at 60 μm/h are reported with 1.01 V 1-sun open-circuit voltage and 23.8% AM1.5G efficiency.

Quaternary sputtering is a promising alternative to more established deposition methods for the fabrication of Cu(In,Ga)Se2 (CIGS) thin films for photovoltaics (PV). In this technique, a single sputtering target containing all four constituents is employed to deposit the CIGS film. Quaternary sputtering offers several advantages over other deposition methods, including excellent uniformity over large areas, high material usage, and less reliance on toxic Se precursors such as H2Se. Despite these advantages, several drawbacks remain. To date, devices fabricated by quaternary sputtering without additional selenization have been limited in efficiency to about 11%, and realizing bandgap grading in order to match the performance of the best evaporated devices presents a challenge. We discuss the prospects for quaternary sputtering as a fabrication technique for CIGS and highlight areas of research that may result in improved performance. Target fabrication and usage is reviewed. We also present results for films and devices including data for the optical constants of sputtered CIGS. Some recent previously unpublished results, including a study of impurities in CIGS sputtering targets and the first demonstration of a CIGS device on a flexible glass substrate, are discussed

Hot-carrier solar cells require absorber materials with restricted carrier thermalization pathways, in order to slow the rate of heat energy dissipation from the carrier population to the lattice, relative to the rate of carrier extraction. Absorber suitability can be characterized in terms of carrier thermalization coefficient (Q). Materials with lower Q generate steady-state hot-carrier populations at lower levels of incident solar power and, therefore, are better able to perform as hot-carrier absorbers. In this study, we evaluate Q = 2.5±0.2 W·K-1 · cm-2 for a In0.52 AlAs/In0.53 GaAs single-quantum-well(QW) heterostructure using photoluminescence spectroscopy. This is the lowest experimentally determined Q value for any material system studied to date. Hot-carrier solar cell simulations, using this material as an absorber yield efficiency ~39% at 2000X, which corresponds to a >5% enhancement over an equivalent single-junction thermal equilibrium device.

Autonomous systems are increasingly used to provide situational awareness and long-term environment monitoring. Photovoltaics (PV) are favored as a long-endurance power source for many of these applications. To date, the use of PV is limited to space and terrestrial (dry-land) installations. The need for a persistent power source also exists for underwater (UW) systems, which currently rely on surface PV arrays or batteries. In this paper, we demonstrate that high-bandgap-InGaP solar cells can provide useful power UW.

This work uses simulations to predict the performance of InAlAsSb solar cells for use as the top cell of triple junction cells lattice matched to InP. The InP-based material system has the potential to achieve extremely high efficiencies due the availability of lattice matched materials close to the ideal bandgaps for solar energy conversion. The band-parameters, optical properties and minority carrier transport properties are modeled based on literature data for the InAlAsSb quaternary, and an analytical drift-diffusion model is used to realistically predict the solar cell performance.

The modeling of high efficiency, multijunction (MJ) solar cells away from the radiative limit is presented. In the model, we quantify the effect of non-radiative recombination by using radiative efficiency as a figure of merit to extract realistic values of performance under different spectral conditions. This approach represents a deviation from the traditional detailed balance approximation, where losses in the device are assumed to occur purely through radiative recombination. For lattice matched multijunction solar cells, the model predicts efficiency values of 37.1% for AM0 conditions and 52.8% under AM1.5D at 1 sun and 500X, respectively. In addition to the theoretical study, we present an experimental approach to achieving these high efficiencies by implementing a lattice matched triple junction (TJ) solar cell grown on InP substrates. The projected efficiencies of this approach are compared to results for the state of the art inverted-metamorphic (IMM) technology. We account for the effect of metamorphic junctions, essential in IMM technology, by employing reduced radiative efficiencies as derived from recent data. We show that high efficiencies, comparable to current GaAs-based MJ technology, can be accomplished without any relaxed layers for growth on InP, and derive the optimum energy gaps, material alloys, and quantum-well structures necessary to realize them.

The radiation response mechanisms operative in space solar cells are described. The effects of electron and proton radiation-induced defects on the cell performance are identified and methods for modeling the radiation response are presented. The space radiation environment is described, and a methodology for modeling the response of a solace cell to exposure to the space radiation environment is presented. It is shown how this model an be used to predict on orbit performance, and examples from space experiments are shown.

We examine thermally evaporated MoO x films as a full-area rear contact to crystalline p-type Si solar cells for efficient hole-selective contacts. Prior to front- and rear-metallization, the implied open-circuit voltage (iV oc) is evaluated to be 646 mV with implied fill factor (iFF) of 82.5% for the tunnel SiO x /MoO x rear contacted cell structure with the passivated emitter on the textured surface, showing it is possible to achieve an implied 1-sun efficiency of 20.8%. Numerical simulation reveals that the electron affinity (kh) of the MoO x material strongly influences the performance of the MoO x contacted p-Si cell. Simulated band diagrams show that the values in kh of the MoO x layer must be sufficiently high in order to lower junction recombination, indicating that the highest efficiency of 21.1% is achievable for a high kh of 5.6 eV of MoO x films and back surface recombination velocity of <100 cm/s at p-Si/MoO x .