| 1. |
- Hultqvist, Adam, et al.
(författare)
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CuGaSe2 solar cells using atomic layer deposited Zn(O,S) and (Zn,Mg)O buffer layers
- 2009
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 517:7, s. 2305-2308
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Tidskriftsartikel (refereegranskat)abstract
- The band gap of Zn(O,S) and (Zn,Mg)O buffer layers are varied with the objective of changing the conduction band alignment at the buffer layer/CuGaSe2 interface. To achieve this, alternative buffer layers are deposited using atomic layer deposition. The optimal compositions for CuGaSe2 solar cells are found to be close to the same for (Zn,Mg)O and the same for Zn(O,S) as in the CuIn0.7Ga0.3Se2 solar cell case. At the optimal compositions the solar cell conversion efficiency for (Zn,Mg)O buffer layers is 6.2% and for Zn(O,S) buffer layers it is 3.9% compared to the CdS reference cells which have 5-8% efficiency.
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| 2. |
- Bose, Sourav, et al.
(författare)
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A morphological and electronic study of ultrathin rear passivated Cu(In,Ga)Se2 solar cells
- 2019
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 671, s. 77-84
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Tidskriftsartikel (refereegranskat)abstract
- The effects of introducing a passivation layer at the rear of ultrathin Copper Indium Gallium di-Selenide Cu(In,Ga)Se2 (CIGS) solar cells is studied. Point contact structures have been created on 25 nm Al2O3 layer using e-beam lithography. Reference solar cells with ultrathin CIGS layers provide devices with average values of light to power conversion efficiency of 8.1% while for passivated cells values reached 9.5%. Electronic properties of passivated cells have been studied before, but the influence of growing the CIGS on Al2O3 with point contacts was still unknown from a structural and morphological point of view. Scanning Electron Microscopy, X-ray Diffraction and Raman spectroscopy measurements were performed. These measurements revealed no significant morphological or structural differences in the CIGS layer for the passivated samples compared with reference samples. These results are in agreement with the similar values of carrier density (~8 x 1016 cm-3) and depletion region (~160 nm) extracted using electrical measurements. A detailed comparison between both sample types in terms of current-voltage, external quantum efficiency and photoluminescence measurements show very different optoelectronic behaviour which is indicative of a successful passivation. SCAPS simulations are done to explain the observed results in view of passivation of the rear interface.
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| 3. |
- Böhnke, Tobias, et al.
(författare)
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Copper indium gallium diselenide thin films for sun angle detectors in space applications
- 2009
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 517:6, s. 2063-2068
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Tidskriftsartikel (refereegranskat)abstract
- This work reports on processing, analysis and characterization of copper indium gallium diselenide (CIGS)used as a photosensitive layer for sensors such as sun angle detectors in space applications. CIGS-based solarcell devices with different CIGS layer thicknesses and the pn-junction located on the opposite side of theincidence of light were illuminated through their ultra-thin transparent molybdenum back contacts. Theresults from the current density versus voltage and quantum efficiency measurement indicate that the CIGSabsorber layer may not exceed 750 nm at backside illumination, due to the limited CIGS diffusion length.
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| 4. |
- Campa, A., et al.
(författare)
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The potential of textured front ZnO and flat TCO/metal back contact to improve optical absorption in thin Cu(In,Ga)Se2 solar cells
- 2007
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 515:15, s. 5968-5972
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Tidskriftsartikel (refereegranskat)abstract
- The role of additionally textured front transparent conductive oxide − TCO (ZnO:Al) and flat TCO/metal contact on optical improvements in thin Cu(In,Ga)Se2 (CIGS) solar cells are investigated by means of numerical simulations. A de-coupled analysis of two effects related to additional texturing of front surface of ZnO:Al TCO − (i) enhancement of light scattering and (ii) decreased total reflectance (antireflective effect) − reveals that the improvements in quantum efficiency, QE, and short-circuit current, JSC, of the solar cell originate from an antireflective effect only. In order to improve optical properties of the back contact the introduction of a TCO layer (undoped ZnO) between CIGS and back metal contact is investigated from the optical point of view. In addition to ZnO/Mo, a highly reflective ZnO/Ag contact (ZnO is also assumed to work as a protection layer for Ag) is also included in simulations. Results show significant increase in reflectance related to introduced ZnO in front of Mo. Drastically increased reflectance is obtained if ZnO/Mo is substituted with ZnO/Ag. The improvements in QE and JSC of a thin CIGS solar cell, related to ZnO/metal contacts are presented.
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| 5. |
- Donzel-Gargand, Olivier, 1986-, et al.
(författare)
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Surface defect passivation by a thin metallic barrier for Cu(InxGa1-x)Se2 co-evaporation on Cr-steel substrates
- 2016
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Ingår i: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 619, s. 220-226
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Tidskriftsartikel (refereegranskat)abstract
- The use of Cr-steel substrates for the fabrication of Cu(In,Ga)Se2 (CIGS) solar cells is highly desirable and is a topic of considerable research interest. However, solar cells on non-treated steel substrates often exhibit decreased performance compared to their homologues on soda lime glass substrates. This is partly attributed to out-diffusion of steel components (Fe, Cr, Mn, etc.) into the solar cell. To avoid this contamination, thin film barriers can be added on top of the steel surface, but they do not always prevent the diffusion completely. In this paper we study the potential of using Cr and Ti as thin barrier layers. We find that local surface defects on the steel, several micrometers in height, lead to cracks in the back contact as well as in the barrier layers. Advanced transmission electron microscopy (TEM) techniques reveal that elemental diffusion and chemical reactions occur at these openings during heat treatments in Se atmosphere. TEM-energy dispersive X-ray spectroscopy (TEM-EDX) analysis in combination with calculation of the solid state diffusion coefficient demonstrate that a Cr-barrier sacrificially protects the Cr-steel substrate, blocking most of the Fe out-diffusion, whereas a Ti-barrier is less efficient.
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| 6. |
- Edoff, Marika, et al.
(författare)
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Technological and economical aspects on the influence of reduced Cu(In,Ga)Se2 thickness and Ga grading for co-evaporated Cu(In,Ga)Se2 modules
- 2011
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Ingår i: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 519:21, s. 7530-7533
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Tidskriftsartikel (refereegranskat)abstract
- Reducing the Cu(In,Ga)Se2 (CIGS) thickness is one way of improving the throughput and capacity in existing production, provided that the efficiency can be kept at a high level. Our experimental results from an in-line co-evaporation process show that it is possible to produce CIGS solar cells with good efficiency at a CIGS thickness of less than 1 µm. An efficiency of 14.4% was obtained for an evaporation time of 8 min and a resulting CIGS thickness of only 0.8 [mu]m. The quantum efficiency measurements show only a minor reduction of the collection in the infrared region that can be related to losses caused by reduced absorption. Passivation of the back contact has been found to be important for thin devices and one way of obtaining good back contact properties, or to reduce the impact of back contact recombination is to use an increased Ga content near the back contact. We have found that Ga grading is feasible also in the three stage process, i.e. a Ga-rich layer near the back contact from stage one is to a high degree retained also after stages two and three. In this paper we discuss the implication of efficiency reduction for the economy of the production and how high efficiency loss that can be tolerated, provided that the output is doubled at equal production cost for the CIGS layer.
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| 7. |
- Igalson, M., et al.
(författare)
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Concentration of defects responsible for persistent photoconductivity in Cu (In,Ga)Se-2 : Dependence on material composition
- 2019
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Ingår i: Thin Solid Films. - : ELSEVIER SCIENCE SA. - 0040-6090 .- 1879-2731. ; 669, s. 600-604
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Tidskriftsartikel (refereegranskat)abstract
- Persistent photoconductivity (PPC) in thin Cu(In,Ga)Se-2 films is discussed within a model of relaxing defects acting as donors or acceptors depending on their configurational and charge state. The aim of this work is to identify the factors related to technological processes which affect the magnitude of PPC. We established a method of evaluation of the concentration of metastable defects in thin Cu(In,Ga)Se-2 films relating it to the position of the Fermi level in thermodynamic equilibrium and used it to compare and discuss the impact of preparation details on the PPC value. The main result is that deviation from Cu/(Ga + In) stoichiometry does not change the concentration of metastable defects. Post deposition annealing in selenium affects the PPC depending on the presence of sodium during the treatment, while the impact of sodium itself on the metastable defect concentration apparently depends on whether it is present during the Cu(In,Ga)Se-2 deposition process or whether it is supplied during post-deposition treatment.
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| 8. |
- Igalson, M., et al.
(författare)
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Metastabilities in the electrical characteristics of CIGS devices : Experimental results vs theoretical predictions
- 2007
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 515:15, s. 6142-6146
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Tidskriftsartikel (refereegranskat)abstract
- Recent theoretical calculations have traced an origin of light- and voltage bias-induced metastabilities in Cu(In,Ga)Se2-based solar cells to negative-U properties of the VSe–VCu complex. In this paper we compare experimental findings with theoretically predicted properties of these defects and calculated values of parameters characteristic for transitions between their different states. Profiles of net acceptor concentrations in the relaxed and metastable states obtained by capacitance profiling have been studied, as well as annealing kinetics of the persistent defect distributions by thermally stimulated capacitance and conductivity. Good qualitative and quantitative agreement are found between theory of VSe-related defects and experimental results. The consequences from the point of view of photovoltaic efficiency of the Cu(In,Ga)Se2-based solar cells are discussed.
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| 9. |
- Igalson, Margaret, et al.
(författare)
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Reinterpretation of defect levels derived from capacitance spectroscopy of CIGSesolar cells
- 2009
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Ingår i: Thin Solid Films. - : Elsevier. - 0040-6090 .- 1879-2731. ; 517:7, s. 2153-2157
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Tidskriftsartikel (refereegranskat)abstract
- In this work we make an attempt to clarify ambiguities and to present our present understanding of defectsand defect-related phenomena affecting the capacitance characteristics of Cu(In,Ga)Se2-based solar cells. Wediscuss deep defect levels derived from admittance and deep level transient spectroscopy, as well as shallowlevels affecting the charge distributions by capacitance–voltage profiling. The discussion includes two typesof metastable effects affecting capacitance characteristics: one induced at room temperature by light orvoltage bias, and one created at low temperature by red illumination of reverse-biased junction (ROB effect).Recent theoretical achievements on negative-U properties of such intrinsic defects as selenium vacancies andInCu antisites are used to explain the experimental data. We show that the most prominent level in theadmittance spectra is due to the response of interface states combined with contribution of deep VSe–VCu−/2−acceptor level. We attribute the ROB metastability to the relaxation of InCu defects upon electron capture.Finally we discuss the influence of these defects on the device efficiency.
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| 10. |
- Igalson, M, et al.
(författare)
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Sub-bandgap photoconductivity and photocapacitance in CIGS thin films and devices
- 2011
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 519:21, s. 7489-7492
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Tidskriftsartikel (refereegranskat)abstract
- Photoconductivity and photocapacitance of Cu(In,Ga)Se(2) and CuGaSe(2) thin films and devices induced by sub-bandgap illumination are investigated. Both effects have been attributed to the optical transition from valence band to the same empty levels situated around 0.8-0.9 eV above the valence band. The influence of the metastable states created by illumination and voltage bias on the sub-bandgap response has been studied. The experimental results are discussed in the framework of a model based on negative-U property of a native defect in chalcopyrites, i.e. V(Se)-V(Cu) divacancy. The arguments are presented that the levels involved in the optical transition observed in photoconductivity and photocapacitance might be antibonding levels of the acceptor configuration of this defect.
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