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- Femtosecond laser (3)
- Chalcopyrite (2)
- Copper indium gallium diselenide (CIGSe) (2)
- Laser-induced forward transfer (LIFT) (2)
- Light concentration (2)
- Micro solar cells (2)
- Absorber optimization (1)
- CuInSe2 (1)
- Indium (1)
- LIFT (1)
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A laser-based bottom-up technique for the fabrication of Cu(In,Ga)Se2 (CIGSe) micro solar cells is presented.
We use femtosecond laser-induced forward transfer (LIFT) to transport a metallic precursor composed of copper, indium, and gallium onto a molybdenum back contact layer on a glass substrate. A CIGSe absorber forms by subsequent selenization. An array of micro absorbers with defined spacing is fabricated to solar cells and characterized under concentrated light illumination. The solar cell array exhibited a conversion efficiency of 1.4‰ at 1 sun as well as a significant efficiency enhancement of 68% rel. under 20-fold concentration. This work demonstrates the possibility of directly grown micrometer-sized solar cells based on chalcogenide absorber layers, enabling effective material usage.
A promising technology in photovoltaics is based on micro-concentrator solar cells, where the photovoltaic active area is realized as an array of sub-millimeter sized cells onto which the incident light is focused via microlenses. This approach allows to increase the cell efficiency and to realize much more compact modules compared to macroscopic concentrator devices. At the same time, expensive raw materials can be saved, which is of interest, for example, with respect to indium in the case of copper-indium-gallium-diselenide (CIGSe) thin film solar cells. Two methods to produce micro-sized precursors of CIGSe absorbers on molybdenum are presented using 30-fs laser pulses at 790 nm wavelength. On the one hand, a multi pulse surface structuring of the molybdenum film or the underlying glass substrate and a subsequent physical vapor deposition were used for a site-selective aggregation of indium droplets. On the other hand, a single pulse laser-induced forward transfer was utilized to selectively deposit combined copper-indium precursor pixels on the molybdenum back contact of the solar cell. Post-processing (selenization, isolation, contacting) of the laser-generated micro-sized precursors results in functional CIGSe solar cells.
Indium is a constituent of copper-indium-gallium-diselenide (CIGSe), which is an excellent absorber material for highly-efficient thin film solar cells but a rare element. A micro-concentrator solar cell design can achieve indium saving along with increased solar cell conversion efficiency. In such a solar cell architecture the CIGSe material is arranged in micrometer sized islands in contrast to the deposition of a thin layer used in standard cells.
In this paper, the production of spatially arranged precursor islands consisting mainly of indium using laser-induced forward transfer (LIFT) is presented. The donor is a glass substrate (150 µm thick) coated with layers of copper (20-150 nm) and indium (200-1000 nm). The receiver is an 800 nm thick molybdenum film on glass intended as back contact for CIGSe solar cells. Islands of the donor material are successfully transferred via LIFT by employing 30-fs laser pulses with 800 nm wavelength and 60 µm focal spot diameter. The spacing between donor and receiver is fixed at 150 µm and the material transfer is performed by a single pulse for each precursor island. The transferred material is characterized by scanning electron and optical microscopy, profilometry and energy dispersive X-ray analyses. Matrices of copper-indium precursors can be transferred in a spatial arrangement adapted to the geometry of micro lens arrays needed for micro-concentrator solar cells.
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).