23 research outputs found
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Characterization and device performance of (AgCu)(InGa)Se2 absorber layers
The study of (AgCu)(InGa)Se2 absorber layers is of interest in that Ag-chalcopyrites exhibit both wider bandgaps and lower melting points than their Cu counterparts. (AgCu)(InGa)Se2 absorber layers were deposited over the composition range 0 < Ag/(Ag+Cu) < 1 and 0.3 < Ga/(In+Ga) < 1.0 using a variety of elemental co-evaporation processes. Films were found to be singlephase over the entire composition range, in contrast to prior studies. Devices with Ga content 0.3 < Ga/(In+Ga) <0.5 tolerated Ag incorporation up to Ag/(Ag+Cu) = 0.5 without appreciable performance loss. Ag-containing films with Ga/(In+Ga) = 0.8 showed improved device characteristics over Cu-only control samples, in particular a 30-40% increase in short-circuit current. An absorber layer with composition Ag/(Ag+Cu) = 0.75 and Ga/(In+Ga) = 0.8 yielded a device with VOC = 890 mV, JSC = 20.5mA/cm2, fill factor = 71.3%, and η = 13.0%
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Characterizing the effects of silver alloying in chalcopyrite CIGS solar cells with junction capacitance methods
A variety of junction capacitance-based characterization methods were used to investigate alloys of Ag into Cu(In1-xGax)Se2 photovoltaic solar cells over a broad range of compositions. These alloys show encouraging trends of increasing VOC with increasing Ag content, opening the possibility of wide-gap cells for use in tandem device applications. Drive level capacitance profiling (DLCP) has shown very low free carrier concentrations for all Ag-alloyed devices, in some cases less than 1014 cm-3, which is roughly an order of magnitude lower than that of CIGS devices. Transient photocapacitance spectroscopy has revealed very steep Urbach edges, with energies between 10 meV and 20 meV, in the Ag-alloyed samples. This is in general lower than the Urbach edges measured for standard CIGS samples and suggests a significantly lower degree of structural disorder
Program Evaluation of the Social Skills Intervention Program with Urban, African-American Kindergartners
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Optical and quantum efficiency analysis of (Ag,Cu)(In,Ga)Se2 absorber layers
(Ag,Cu)(In,Ga)Se2 thin films have been deposited by elemental co-evaporation over a wide range of compositions and their optical properties characterized by transmission and reflection measurements and by relative shift analysis of quantum efficiency device measurements. The optical bandgaps were determined by performing linear fits of (αhν)2 vs. hν, and the quantum efficiency bandgaps were determined by relative shift analysis of device curves with fixed Ga/(In+Ga) composition, but varying Ag/(Cu+Ag) composition. The determined experimental optical bandgap ranges of the Ga/(In+Ga) = 0.31, 0.52, and 0.82 groups, with Ag/(Cu+Ag) ranging from 0 to 1, were 1.19-1.45 eV, 1.32-1.56 eV, and 1.52-1.76 eV, respectively. The optical bowing parameter of the different Ga/(In+Ga) groups was also determined
CdTe and CuInGaSe2 Thin-Film Solar Cells
Thin film solar cells are based on materials, which show an extraordinary high absorption coefficient so that there is no need to build thick solar cells to absorb all the light. Using this kind of materials allows one to fabricate devices with an overall thickness of less than 10 micrometers and a clear advantage in terms of material supply and fabrication energy. Thin-film solar cells offer a wide variety of choices in terms of device design, fabrication methods and substrates (flexible or rigid, metal or insulator). The deposition of different layers (contact, buffer, absorber, reflector, etc.) can be done using several techniques, which will be described later. Indeed, such versatility allows for tailoring and engineering of the layers, in order to match the solar spectrum and to improve device performance. Typically, the thin films used in these devices are polycrystalline materials, where the layer is a pattern of small crystals, whose width can range between 0.1 and 5 \uf06dm. As shown in Figure 8.1, the layer is a patch of differently sized grains with different orientations. This configuration looks very disordered and irregular considering that it has to allow carriers to move through the material; however the films, when properly prepared, have the required conductivity, and devices can reach very high efficiencies up to 25%. On the other hand, the advantage of such a disordered structure is that it does not need a very precise control of crystal growth; neither does it need high energy for crystallization: this is an advantage compared to other technologies such as crystalline silicon