A German research team has developed CuInSe₂ microconcentrator solar cells using laser-assisted metal-organic chemical vapor deposition to grow indium islands directly on molybdenum-coated glass, forming absorber arrays without masks or patterns. The not yet optimized micromodules achieved an efficiency of up to 0.65% under one sun, with gains of up to 250% under concentrated lighting.
A research team in Germany has developed a copper, indium and selenium (CuInSe₂) micro-concentrator solar device consisting of vertically grown absorber islands on molybdenum (Mo) films.
The scientists used laser-assisted metal-organic chemical vapor deposition (LA-MOCVD) to grow indium (In) islands in a bottom-up approach, rather than depositing a continuous thin film and then patterning it. “The main novelty of our work is the use of an LA-MOCVD method for the bottom-up growth of indium precursor islands,” said corresponding author Jan Berger. pv magazine. “This approach proved to be a fast and reliable technique for simultaneous local growth, especially offering the possibility of adding gallium and copper locally using the same method.”
“The most unexpected finding was that the indium precursor islands formed separate cluster structures that stayed in place and refused to coalesce into one large island – even after annealing above the melting temperature of indium,” he added. “Moreover, it was surprising to see that the structural features of these precursor islands remained clearly visible even after the selenization process.”
Device fabrication starts with glass substrates coated with Mo, which are then processed by LA-MOCVD. In this step, a laser array locally heats the substrate. It decomposes the precursor gas only in certain spots, creating a 7 x 7 array of indium islands without the need for masks or cartridges. A thin copper layer is then deposited and the stack is selenized to form CuInSe2 absorber islands.
Image: Universität Duisburg-Essen (UDE), Solar energy materials and solar cells, CC BY 4.0
Then the samples are etched to remove unwanted material, coated with photoresist for electrical insulation, and patterned with a laser to form openings. The solar cell is then completed by depositing a cadmium sulfide (CdS) buffer layer, followed by intrinsic zinc oxide (i-ZnO) and aluminum-doped zinc oxide (AZO) window layers. Finally, each array of 49 microcells is contacted and measured as a single module, with a glass/Mo/CIS absorber/cadmium sulfide (CdS)/i-ZnO/AZO device structure.
In total, the team produced nine micromodules and tested four. Initial measurements were performed under one sun, followed by increasing intensities up to 17 suns to simulate concentrator conditions. These not yet optimized arrays achieved a conversion efficiency of up to 0.65% under one sun, with efficiency increasing at higher illumination: gains of approximately 60% at lower concentrations and up to 250% at 17 suns.
“Functional devices were successfully produced, but notable key challenges were identified, particularly related to the intensity distribution of the diffractive optical element (DOE), the initial morphology of indium islands and the repeatability of processes. Addressing these challenges in material quality and process control is essential,” the team explains. “Once solved, the LA-MOCVD method holds great promise as a rapid and resource-efficient production technique for next-generation micro-concentrator photovoltaics.”
The new cell concept was presented in “CuInSe2-based micro-concentrator solar cells fabricated from In islands grown by laser-assisted MO-CVD”, published in Solar energy materials and solar cells. Scientists from Germany’s University of Duisburg-Essen, the Leibniz Institute for Crystal Growth, the Federal Institute for Materials Research and Testing, the Brandenburg Technical University Cottbus-Senftenberg and the engineering firm Bestc participated in the study.
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