Laser Direct Write Processes for developing new energy devices
Laser Direct Write Processes for developing new energy devices:
- Laser processes for material treatment and patterning (laser ablation – substrative process)
- Laser processes to deposit metals and dielectrics (Laser Induced Forward Transfer LIFT – additive process)
In the project SCALED several Laser Direct Write Processes will be study to develop new energy devices.
Laser ablation of non-conventional materials
The CL-UPM has already developed the procedures to ablate materials conventionally used in PV technology, such as thin silicon films, standard transparent electrodes or metallic layers. This well-stablished procedure will be used on a variety of non usual materials to customize the ablation of thin-films and to minimize the damage on the surrounding regions studying the process with lasers with different wavelength and pulse duration.
Laser transfer of metals and dielectrics
The laser-induced forward-transfer (LIFT) of silver pastes has been studied before on silicon-based devices at CL-UPM. In this project, the alternative materials under study are typically much less stable and the LIFT process needs to be optimized to avoid a direct shunting of the layers when they receive the transferred material. In addition, the sintering step that follows the LIFT process is typically done at relatively high temperatures (300 oC) that could degrade the thin-films under study. In that case, alternative methods like a laser-sintering for a more local heating will be evaluated.
In this project, the transference of insulating materials will be also studied, as it can be very helpful for an interconnection of devices with metallic layers deposited at different levels.
Influence of the Gap between Substrates in the Laser-Induced Transference of High-Viscosity Pastes.
Laser-induced forward transfer for high-viscosity—of Pa·s—pastes differ from standard LIFT processes in its dynamics. In most techniques, the transference after setting a great gap does not modify the shape acquired by the fluid, so it stretches until it breaks into droplets. In contrast, there is no transferred material when the gap is bigger than three times the paste thickness in LIFT for high-viscosity pastes, and only a spray is observed on the acceptor using this configuration. In this work, the dynamics of the paste have been studied using a finite-element model in COMSOL Multiphysics, and the behavior of the paste varying the gap between the donor and the acceptor substrates has also been modeled. The paste bursts for great gaps, but it is confined when the acceptor is placed close enough. The obtained simulations have been compared with a previous work, in which the paste structures were photographed. The analysis of the simulations in terms of speed allows for predicting the burst of the paste—spray regime—and the construction of a printability map regarding the gap between the substrates.
LIFT front-contact metallization of silicon solar cells
Laser-Induced Forward Transfer (LIFT) is a very versatile technique, allowing the selective transfer of a wide range of materials with no contact and high accuracy. This work includes the analysis of heterojunction silicon solar cells with the frontal grid deposited by LIFT, and the electric characterization of the deposited lines.
Cavitation bubble evidence in BA-LIFT processes
Blister-Actuated Laser-Induced Forward Transfer (BA-LIFT) is a modified LIFT process to avoid the direct interaction between the laser pulse and the transference fluid. In a previous study, the comparison between process images and simulation suggested the existence of a mechanically induced cavitation bubble. In this work, new images have been acquired to evaluate its appearance due to the depressurization of the fluid in the front of the polyimide blister.