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- Hatami, Sepehr, 1981, et al.
(författare)
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Optimised selection of processing routes for sintered parts manufacture: A component-oriented approach
- 2009
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Ingår i: Advances in Powder Metallurgy and Particulate Materials - 2009, Proceedings of the 2009 International Conference on Powder Metallurgy and Particulate Materials, PowderMet 2009. - Princeton, N.J. : Metal Powder Industries Federation. - 9780981949611 ; , s. 139-1323
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Konferensbidrag (refereegranskat)abstract
- To stay competitive, PM manufacturers have to be able to accept a wide range of components with different features and properties. Thus, it is of utmost importance for manufacturers to adapt their common process routes to new requirements as rapidly and economical as possible. The procedure of identifying the right route among all the alternatives requires abundance of experience and knowledge and is a crucial and time-consuming decision; usually made by a team of engineers. In this study, by considering the mechanical properties and design specifications of the final component, a simple methodology is developed to aid the engineer(s) in selection of the optimum PM process route. In order to sort the possible routes according to cost, a cost estimating module has been devised. The total concept is applied to a case study and its accuracy has been evaluated.
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- Malm, Ulf, et al.
(författare)
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Determination of dominant recombination paths in Cu(In,Ga)Se2 thin-film solar cells with ALD-ZnO buffer layers
- 2005
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 480-481, s. 208-212
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Tidskriftsartikel (refereegranskat)abstract
- CuIn1−xGaxSe2 (CIGS) and CuInSe2 (CIS) thin-film solar cells, with ZnO buffer layers deposited by Atomic Layer Deposition (ALD), are examined with respect to dominant recombination path. They are compared with reference cells with CdS buffer layers. The principal method of examination is temperature-dependent J–V characterization (J(V)T), and the analysis of the J(V)T data has been modified in order to more reliably discern the dominant recombination path.Compared to the CIS cells with the traditional CdS buffer layer, the CIS cells with ALD–ZnO buffer layer exhibit the same dominant recombination path, i.e., recombination in the bulk of the absorber. For the CIGS cells (with [Ga]/([Ga]+[In])=0.3), however, the analysis of the cells with ALD–ZnO buffer points to dominant interface recombination, while the CdS buffer cells are dominated by bulk recombination.For CIGS, the difference between the recombination in ALD–ZnO and CdS cells is consistent with the negative conduction band offset found by photoelectron spectroscopy in these ALD–ZnO cells in a previous study. This offset leads to increased interface recombination.For CIS/ALD–ZnO, it was previously found that there is no negative conduction band offset since the conduction band minimum of the absorber is lower. Consistently there is no difference in dominant recombination path between ALD–ZnO buffer cells and traditional CdS buffer cells.
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- Malm, Ulf, 1978-
(författare)
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Modelling and Degradation Characteristics of Thin-film CIGS Solar Cells
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Thin-film solar cells based around the absorber material CuIn1-xGaxSe2 (CIGS) are studied with respect to their stability characteristics, and different ways of modelling device operation are investigated. Two ways of modelling spatial inhomogeneities are detailed, one fully numerical and one hybrid model. In the numerical model, thin-film solar cells with randomized parameter variations are simulated showing how the voltage decreases with increasing material inhomogeneities.With the hybrid model, an analytical model for the p-n junction action is used as a boundary condition to a numerical model of the steady state electrical conduction in the front contact layers. This also allows for input of inhomogeneous material parameters, but on a macroscopic scale. The simpler approach, compared to the numerical model, enables simulations of complete cells. Effects of material inhomogeneities, shunt defects and grid geometry are simulated.The stability of CIGS solar cells with varying absorber thickness, varying buffer layer material and CIGS from two different deposition systems are subjected to damp heat treatment. During this accelerated ageing test the cells are monitored using characterization methods including J-V, QE, C-V and J(V)T. The degradation studies show that the typical VOC decrease experienced by CIGS cells subjected to damp heat is most likely an effect in the bulk of the absorber material.When cells encapsulated with EVA are subjected to the same damp heat treatment, the effect on the voltage is considerably reduced. In this situation the EVA is saturated with moisture, representing a worst case scenario for a module in operation. Consequently, real-life modules will not suffer extensively from the VOC degradation effect, common in unprotected CIGS devices.
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- Malmström, Jonas, 1975-
(författare)
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On Generation and Recombination in Cu(In,Ga)Se2 Thin-Film Solar Cells
- 2005
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The solar cell technology based on Cu(In,Ga)Se2 (CIGS) thin-films provides a promising route to cost competitive solar electricity. The standard device structure is ZnO:Al/ZnO/CdS/CIGS/Mo films on a glass substrate, where the first three layers are n-type semiconductors with wide bandgaps, forming a pn-junction with the p-type CIGS absorber layer; the Mo layer serves as a back contact. This thesis deals with analysis of the generation and recombination of electron-hole pairs throughout the device. These processes determine the maximum output power: generation limits the current; recombination limits the voltage.The generation is calculated with an optical model based on complex refractive indices determined for the individual layers. The main features of the optical response of the solar cell can be reproduced with a specular model neglecting scattering. A model including ideally Lambertian scattering at the front and back surface of the CIGS absorber layer is introduced to investigate the possibility to maintain a high current generation with thin absorber layers. The result highlights the relatively poor optical performance of the Mo back contact. TiN and ZrN are explored as alternatives, and improved optical performance is experimentally demonstrated for both materials.The recombination analysis emphasizes that, in general, more than one recombination path of comparable magnitude are operative in parallel. For cells with absorber bandgap increasing from 1.0 eV (CuInSe2) to 1.7 eV (CuGaSe2), a relative increase of interface recombination is found. When these cells are subject to accelerated ageing, degradation is smallest for intermediate bandgaps; an explanation involving different sensitivity to decreased absorber band bending and activation of grain boundaries is suggested. The optical gain with ZrN back contacts is counteracted by increased back contact recombination and contact resistance, but an intermediate layer of MoSe2 is shown to alleviate these problems, allowing for an overall improved efficiency.
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