| 1. |
- Jensfelt, Patric, et al.
(författare)
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A framework for vision based bearing only 3D SLAM
- 2006
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Ingår i: Proceedings of the 2006 IEEE International Conference on Robotics and Automation, Orlando, Florida - May 2006. - : IEEE. - 0780395050 ; , s. 1944-1950
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Konferensbidrag (refereegranskat)abstract
- This paper presents a framework for 3D vision based bearing only SLAM using a single camera, an interesting setup for many real applications due to its low cost. The focus in is on the management of the features to achieve real-time performance in extraction, matching and loop detection. For matching image features to map landmarks a modified, rotationally variant SIFT descriptor is used in combination with a Harris-Laplace detector. To reduce the complexity in the map estimation while maintaining matching performance only a few, high quality, image features are used for map landmarks. The rest of the features are used for matching. The framework has been combined with an EKF implementation for SLAM. Experiments performed in indoor environments are presented. These experiments demonstrate the validity and effectiveness of the approach. In particular they show how the robot is able to successfully match current image features to the map when revisiting an area.
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| 2. |
- Marko, Hakim, et al.
(författare)
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Effects of CuIn0,5Ga0,5Se2 growth by isothermal and bithermal Cu-Poor/Rich/Poor sequence on solar cells properties
- 2009
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Ingår i: Thin-Film Compound Semiconductor Photovoltaics — 2009. - Warrendale, PA : Material Research Society.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Co-evaporated CuIn0,5Ga0,5Se2 thin film solar cells were grown using a sequential Cu-Poor/Rich/Poor process (CUPRO). During the growth process, the substrate temperature was either kept constant at 570 °C (iso-CUPRO) or decreased during the first step to either 360 or 430 or 500 °C (bi-CUPRO). According to atomic force microscopy (AFM) measurements, the lower the temperature is in the first step the smoother the final CIGS surface becomes. By decreasing the first step temperature, cross-section scanning electron microscopy (SEM) and q-2q x-ray diffraction (XRD) do not reveal clearly any important changes of morphology and crystallographic preferred orientation. SLG/Mo/CIGS/Buffer layer/i-ZnO/ZnO:Al/grid(Ni/Al/Ni)solar cells with either a chemical bath deposited CdS or an atomic layer deposited Zn(O,S) buffer layer were fabricated. For both buffer layers, the bi-CUPRO processes lead to higher efficiencies. Besides, using Zn(O,S), the electronic collection was improved for the infrared spectrum as well as for the ultraviolet spectrum. This resulted in efficiencies close to 14,5 % for the Zn(O,S) cells.
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| 3. |
- Platzer-Björkman, Charlotte, 1976-
(författare)
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Band Alignment Between ZnO-Based and Cu(In,Ga)Se2 Thin Films for High Efficiency Solar Cells
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Thin-film solar cells based on Cu(In,Ga)Se2 contain a thin buffer layer of CdS in their standard configuration. In order to avoid cadmium in the device for environmental reasons, Cd-free alternatives are investigated. In this thesis, ZnO-based films, containing Mg or S, grown by atomic layer deposition (ALD), are shown to be viable alternatives to CdS. The CdS is an n-type semiconductor, which together with the n-type ZnO top-contact layers form the pn-junction with the p-type Cu(In,Ga)Se2. From device modeling it is known that a buffer layer conduction band (CB) position of 0-0.4 eV above that of the Cu(In,Ga)Se2 layer is consistent with high photovoltaic performance. For the Cu(In,Ga)Se2/ZnO interface this position is measured by photoelectron spectroscopy and optical methods to –0.2 eV, resulting in increased interface recombination. By including sulfur into ZnO, a favorable CB position to Cu(In,Ga)Se2 can be obtained for appropriate sulfur contents, and device efficiencies of up to 16.4% are demonstrated in this work. From theoretical calculations and photoelectron spectroscopy measurements, the shift in the valence and conduction bands of Zn(O,S) are shown to be non-linear with respect to the sulfur content, resulting in a large band gap bowing. ALD is a suitable technique for buffer layer deposition since conformal coverage can be obtained even for very thin films and at low deposition temperatures. However, deposition of Zn(O,S) is shown to deviate from an ideal ALD process with much larger sulfur content in the films than expected from the precursor pulsing ratios and with a clear increase of sulfur towards the Cu(In,Ga)Se2 layer. For (Zn,Mg)O, single-phase ZnO-type films are obtained for Mg/(Zn+Mg) < 0.2. In this region, the band gap increases almost linearly with the Mg content resulting in an improved CB alignment at the heterojunction interface with Cu(In,Ga)Se2 and high device efficiencies of up to 14.1%.
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| 4. |
- Platzer Björkman, Charlotte, et al.
(författare)
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Optimization of ALD-(Zn,Mg)O buffer layers and (Zn,Mg)O/Cu(In,Ga)Se-2 interfaces for thin film solar cells
- 2007
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 515:15, s. 6024-6027
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Tidskriftsartikel (refereegranskat)abstract
- (Zn,Mg)O films, fabricated by atomic layer deposition, ALD, are investigated as buffer layers in Cu(In,Ga)Se2-based thin film solar cells. Optimization of the buffer layer is performed in terms of thickness, deposition temperature and composition. High efficiency devices are obtained for deposition at 105–135 °C, whereas losses in open circuit voltage are observed at higher deposition temperatures. The optimal compositional region for (Zn,Mg)O buffer layers in this study is for Mg/(Zn + Mg) contents of about 0.1–0.2, giving band gap values of 3.5–3.7 eV. These devices appear insensitive to thickness variations between 80 and 600 nm. Efficiencies of up to 16.2% are obtained for completely Cd- and S-free devices with (Zn,Mg)O buffer layers deposited with 1000 cycles at 120 °C and having a band gap of 3.6 eV.
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| 5. |
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| 6. |
- Platzer Björkman, Charlotte, et al.
(författare)
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Zn(O,S) buffer layers by atomic layer deposition in Cu(In,Ga)Se-2 based thin film solar cells : Band alignment and sulfur gradient
- 2006
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 100:4, s. 044506-
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Tidskriftsartikel (refereegranskat)abstract
- Thin film solar cells with the structure soda lime glass/Mo/Cu(In,Ga)Se-2/Zn(O,S)/ZnO/ZnO:Al are studied for varying thickness and sulfur content of the Zn(O,S) buffer layer. These Zn(O,S) layers were deposited by atomic layer deposition (ALD) at 120 degrees C. Devices with no or small concentrations of sulfur in the buffer layer show low open-circuit voltages. This is explained by the cliff, or negative conduction-band offset (CBO), of -0.2 eV measured by photoelectron spectroscopy (PES) and optical methods for the Cu(In,Ga)Se-2 (CIGS)/ZnO interface. Devices with ZnS buffer layers exhibit very low photocurrent. This is expected from the large positive CBO (spike) of 1.2 eV measured for the CIGS/ZnS interface. For devices with Zn(O,S) buffer layers, two different deposition recipes were found to yield devices with efficiencies equal to or above reference devices in which standard CdS buffer layers were used; ultrathin Zn(O,S) layers with S/Zn ratios of 0.8-0.9, and Zn(O,S) layers of around 30 nm with average S/Zn ratios of 0.3. The sulfur concentration increases towards the CIGS interface as revealed by transmission electron microscopy and in vacuo PES measurements. The occurrence of this sulfur gradient in ALD-Zn(O,S) is explained by longer incubation time for ZnO growth compared to ZnS growth. For the Zn(O,S) film with high sulfur content, the CBO is large which causes blocking of the photocurrent unless the film is ultrathin. For the Zn(O,S) film with lower sulfur content, a CBO of 0.2 eV is obtained which is close to ideal, according to simulations. Efficiencies of up to 16.4% are obtained for devices with this buffer layer.
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| 7. |
- Törndahl, Tobias, et al.
(författare)
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Atomic layer deposition of Zn1-xMgxO buffer layers for Cu(In,Ga)Se2 solar cells
- 2007
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Ingår i: Progress in Photovoltaics. - : Wiley. - 1062-7995 .- 1099-159X. ; 15:3, s. 225-235
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Tidskriftsartikel (refereegranskat)abstract
- Fabrication of Zn1-xMgxO films by atomic layer deposition (ALD) has been studied for use as buffer layers in Cu(In,Ga)Se2 (CIGS)-based solar cell devices. The Zn1-xMgxO films were grown using diethyl zinc, bis-cyclopentadienyl magnesium and water as precursors in the temperature range from 105 to 180°C. Single-phase ZnO-like films were obtained for x < 0·2, followed by a two phase region of ZnO- and MgO-like structures for higher Mg concentrations. Increasing optical band gaps of up to above 3·8 eV were obtained for Zn1-xMgxO with increasing x. It was found that the composition of the Zn1-xMgxO films varied as an effect of deposition temperature as well as by increasing the relative amount of magnesium precursor pulses during film growth. Completely Cd-free CIGS-based solar cells devices with ALD-Zn1-xMgxO buffer layers were fabricated and showed efficiencies of up to 14·1%, which was higher than that of the CdS references.
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