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- Femtosecond laser patterning (2)
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- Micro-concentrator solar cell (2)
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- CIGSe (1)
- CIGSe micro solar cells (1)
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Organisationseinheit der BAM
A unique direct electrodeposition technique involving very high current densities, high voltages and high electrolyte concentrations is applied for highly selective mass synthesis of stable, isolable, surfactant-free, single-crystalline Bi hexagons on a Cu wire at room temperature. A formation mechanism of the hexagons is proposed. The morphology, phase purity, and crystallinity of the material are well characterized by FESEM, AFM, TEM, SAED, EDX, XRD, and Raman spectroscopy. The thermal stability of the material under intense electron beam and intense laser light irradiation is studied. The chemical stability of elemental Bi in nitric acid shows different dissolution rates for different morphologies. This effect enables a second way for the selective fabrication of Bi hexagons. Bi hexagons can be oxidized exclusively to α-Bi2O3 hexagons. The Bi hexagons are found to be promising for thermoelectric applications. They are also catalytically active, inducing the reduction of 4-nitrophenol to 4-aminophenol. This electrodeposition methodology has also been demonstrated to be applicable for synthesis of bismuth-based bimetallic hybrid composites for advanced applications.
Electrical and optical applications based on micro- and nanoparticles have specific demands on their interfacial properties. These properties are strongly related to atmospheric conditions to which the particles were exposed during their formation. In this study, metallic In microparticles are synthesized by solidification of In droplets on an amorphous Mo substrate at normal pressure and under vacuum conditions. The influence of ambient pressure on the interface and surface shape is investigated. While solidification at atmospheric pressure leads to collapsed particles with undisturbed contact to the substrate, low pressures result in smooth spherical particles but with cavities inside. Numerical simulations with COMSOL Multiphysics reveal different temperature profiles and heat flux in particles during solidification for both cases. This indicates different starting conditions of the solidification, which leads to the described phenomenon eventually. The investigation of the varying process conditions on the particle shape in combination with the calculated and measured temperature curves over time gives valuable insights into new approaches to synthesize micro- and nanoparticles with defined interfacial properties. Both ambient pressure and cooling rate provide well-controllable and reliable parameters for the realization of different interfacial shapes.
A bottom-up approach is presented for the production of arrays of indium islands on a molybdenum layer on glass, which can serve as micro-sized precursors for indium compounds such as copper-indium-gallium-diselenide used in photovoltaics. Femtosecond laser ablation of glass and a subsequent deposition of a molybdenum film or direct laser processing of the molybdenum film both allow the preferential nucleation and growth of indium islands at the predefined locations in a following indium-based physical vapor deposition (PVD) process. A proper choice of laser and deposition parameters ensures the controlled growth of indium islands exclusively at the laser ablated spots. Based on a statistical analysis, these results are compared to the non-structured molybdenum surface, leading to randomly grown indium islands after PVD.
Indium islands on molybdenum coated glass can be grown in ordered arrays by surface structuring using a femtosecond laser. The effect of varying the molybdenum coated glass substrate temperature and the indium deposition rate on island areal density, volume and geometry is investigated and evaluated in a physical vapor deposition (PVD) process. The joined impact of growth conditions and spacing of the femtosecond laser structured spots on the arrangement and morphology of indium islands is demonstrated. The results yield a deeper understanding of the island growth and its precise adjustment to industrial requirements, which is indispensable for a technological application of such structures at a high throughput, for instance as precursors for the preparation of Cu(In,Ga)Se2 micro concentrator solar cells.
Micro-concentrator solar cells offer an attractive way to further enhance the efficiency of planar-cell technologies while saving absorber material. Here, two laser-based bottom-up processes for the fabrication of regular arrays of CuInSe2 and Cu(In,Ga)Se2 microabsorber islands are presented, namely one approach based on nucleation and one based on laser-induced forward transfer.
Additionally, a procedure for processing these microabsorbers to functioning micro solar cells connected in parallel is demonstrated. The resulting cells show up to 2.9% efficiency and a significant efficiency enhancement under concentrated Illumination.
A procedure to fabricate CuInSe2 (CISe) micro-absorbers and solar cells for concentrator applications is presented. The micro-absorbers are developed from indium precursor islands, which are deposited on a molybdenum coated glass substrate (back contact), followed by deposition of copper on top and subsequent selenization as well as selective etching of copper selenides. In order to compare the properties of the locally grown absorbers to those of conventional large area CISe films, we systematically examine the compositional and morphological homogeneity of the micro absorbers and carry out photoluminescence measurements. Preliminary devices for micro-concentrator solar cell applications are fabricated by optimizing the copper to indium ratio and the size of the indium precursor islands. The resulting micro solar cells provide a characteristic I–V curve under standard illumination conditions (1 sun).
Single-pulse femtosecond laser-induced forward transfer (LIFT, 30 fs, 790 nm) is used to deposit micron-sized dots of copper and/or indium onto a molybdenum layer on glass. Such systems can serve as precursors for the bottom-up manufacturing of micro-concentrator solar cells based on copper-indium-gallium-diselenide. The influence of the thickness of the copper, indium and combined copper-indium donor layers on the quality of the transferred dots was qualified by scanning electron microscopy, energy-dispersive X-ray analysis, and optical microscopy. The potential for manufacturing of a spatial arrangement adapted to the geometry of micro-lens arrays needed for micro-concentrator solar cells is demonstrated.