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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 thin-film solar cells. Different approaches 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 or the underlying glass substrate and a subsequent physical vapor deposition (PVD) process were used for a site-selective aggregation of indium droplets. On the other hand, a single pulse laser-induced forward transfer (LIFT) was utilized to selectively deposit combined copper/indium/gallium precursor pixels on the molybdenum back contact of the solar cell. It was demonstrated that a postprocessing of the laser-generated micro-sized precursors results in an array of working CIGSe solar cells with an efficiency of 2.9% for 1 sun Illumination.
Thin film solar cells made of Cu(In,Ga)Se2 (CIGSe) suffer from high costs, since the rare elements indium and gallium are used for a multitude of technical applications. The concept of micro-concentrator CIGSe solar cells allows substantial material saving. Therefore a reliable bottom up process for the preparation of the absorber islands is required. In addition, this also results in an increase of solar cell efficiency. We show that the indium islands can be grown at predefined locations by novel methods of surface treatment before indium deposition. By this, regular island patterns with a well-defined morphology have been obtained. The controlled deposition of copper, followed by selenization in a PVD system, and selective etching of copper selenides yields polycrystalline CIGSe micro islands with promising material properties. For the samples, we proof ways to place a non-conducting layer in between CIGSe islands to insulate the front and back contact. This layer is obtained by spin-coating and curing a novolak based resist. At first, the photovoltaic active absorber islands is completely covered by the resin. The top of the islands can be stripped by plasma etching for front contacting. A characterization of the obtained devices provided evidence for their functionality.
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 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).