The RALPH project builds on the laser‑doping and laser‑densification results obtained in the earlier LASSIE programme (FKZ 0324143A) and the APPI collaboration with Fraunhofer ISE (FKZ 0325895B). In LASSIE, Gebr. Schmid GmbH and the University of Konstanz demonstrated that a single laser irradiation of chemical‑vapour‑deposited (CVD) layers can introduce a high concentration of phosphorus into n‑type silicon wafers before any thermal step. The subsequent anneal not only heals laser‑induced crystal damage but also optimises the dopant profile, yielding locally highly doped regions with excellent electronic performance. This approach replaces the conventional, costly mask‑based doping steps.

The RALPH effort focuses on simplifying the production of interdigitated back‑contact (IBC) high‑efficiency solar cells. By exploiting the laser‑induced densification of the BSG (back‑side glass) layer, the project creates a local etch stop: after laser treatment, the densified layer shows a reduced etch rate in hydrofluoric acid, allowing selective removal of the underlying silicon without a mask. Laser ablation of the APCVD a‑Si layer is also explored; appropriate laser parameters can remove the thin film entirely, again without the need for a separate masking process. In addition, laser doping from a PSG (phosphosilicate glass) layer has been shown to deliver the desired phosphorus concentration while keeping the process simple.

A key technical milestone is the integration of all these laser steps into a single thermal cycle. The aim is to generate both the n‑ and p‑doped regions of the IBC cell and to form the front‑ and back‑side thermal‑oxide passivation layers in one heat treatment, thereby eliminating the need for screen‑printing, inkjet, or other mask technologies. The process uses only conventional equipment, with the laser system being the sole additional component. The project also investigates the influence of metallisation on laser damage and the alignment of laser‑doped regions with subsequent screen‑printed contacts, ensuring reliable electrical performance.

The expected outcome is an industrial‑scale IBC cell measuring 156 × 156 mm² that achieves an efficiency exceeding 23 %. This target is based on the performance of cells fabricated in the LASSIE pilot runs and represents a significant step toward making IBC technology competitive in mainstream markets. By reducing the number of process steps and eliminating expensive mask fabrication, the RALPH project aims to lower the cost per watt‑peak of high‑efficiency modules.

Collaboration in the project involves Gebr. Schmid GmbH, the University of Konstanz, and Fraunhofer ISE, with each partner contributing expertise in laser processing, silicon device fabrication, and process integration. The funding comes from the German research programme, with the LASSIE and APPI projects providing the foundational results that RALPH extends. Over the course of the project, the partners have produced several publications detailing the laser‑induced doping mechanisms, densification effects, and the integration of these steps into a single thermal cycle. The combined effort demonstrates that laser technology can replace traditional mask‑based doping and passivation steps, offering a pathway to lower‑cost, high‑efficiency IBC solar cells.