The project “EN DURCH – Laser‑induced structure formation on surfaces – COSTSOL – Pilot projects: project coordination and growth of laser tools, selective ablation of indium and gallium in the MOCVD chamber” was carried out under the German Federal Ministry of Education and Research (BMBF) with the grant number 03EE1029A and was coordinated by the Forschungsverbund Berlin e.V. in Berlin. The consortium combined expertise from laser technology, photonics, materials science and photovoltaics. A key partner was the Institute for Materials Research (IKZ), which supplied the vacuum chambers and the expertise in crystalline material growth, while laser‑optics companies supplied the laser source and the custom diffractive optical element (DOE). The project ran for three years, concluding in December 2023, and aimed to demonstrate a mask‑free, lithography‑free method for creating micro‑scale crystalline islands of Cu(In,Ga)Se₂ (CIGSe) on amorphous glass substrates, a critical step toward micro‑concentrator solar cells.

Technically, the core innovation was the use of a focused laser beam shaped by a DOE to deliver a patterned energy distribution onto the substrate. The resulting thermal gradients caused selective melting and crystallization of the deposited amorphous precursor. By tuning the laser wavelength and pulse energy, the team achieved localized ablation of indium and gallium from the precursor, thereby initiating nucleation of indium islands through the laser‑induced decomposition of trimethylindium or triethylindium. These islands served as seeds for subsequent growth of CIGSe micro‑islands. The process combined physical vapor deposition (PVD) for initial film deposition, chemical vapor deposition (CVD) for controlled growth, and a reactive annealing step in a hydrogen‑sulfur atmosphere to achieve the desired stoichiometry and electrical properties. The integrated system, comprising a laser source, DOE, vacuum chambers, and a handler for inter‑chamber transfer, allowed batch processing without breaking vacuum, a significant advantage for scalability.

The experimental results demonstrated the formation of crystalline CIGSe islands with diameters of approximately 10 µm and a regular spacing of 1–3 mm, matching the requirements for placement under commercial micro‑lens arrays. Scanning electron microscopy revealed well‑defined island edges and a uniform crystalline texture, while X‑ray diffraction confirmed the chalcopyrite phase. Photovoltaic testing of prototype micro‑concentrator cells fabricated on these islands showed an open‑circuit voltage of 0.55 V and a short‑circuit current density of 12 mA cm⁻², indicating that the laser‑induced growth method produces material with performance comparable to conventional deposition techniques. The DOE‑shaped laser patterning also allowed the creation of arbitrary island geometries, demonstrating the flexibility of the approach for future device architectures.

Collaboration-wise, the project was structured around clear roles: the laser‑optics partner designed and fabricated the DOE and integrated the laser system; the IKZ handled the vacuum chamber assembly, process development, and material characterization; and the Forschungsverbund Berlin e.V. coordinated the overall project, managed the budget, and facilitated communication between partners. The consortium also engaged with industry stakeholders to assess the commercial viability of the technology, and the results were disseminated through conference presentations and a planned publication in a peer‑reviewed journal. The project’s outcomes align with the BMBF’s objectives of advancing high‑performance photovoltaic technologies and demonstrate a viable pathway toward scalable, mask‑free fabrication of micro‑concentrator solar cells.