Fraunhofer Institute for Solar Energy Systems ISEAt Fraunhofer ISE, we are conducting research on lasers as an alternative heat source for heating industrial furnaces. Thermal processes are essential in the manufacture of solar cells, e.g., for contact annealing, the suppression of LeTID (light- and temperature-induced degradation), the regeneration of BO defects (boron-oxygen), perovskite crystallization, or hydrogen engineering. Not only photovoltaics, but also other industries such as power electronics and fuel cell production require advanced heat treatment for annealing or for drying and sintering of pastes and powders. Laser-based heating processes enable a high degree of flexibility in terms of temporal modulation and spatial control. We reduce process times while simultaneously improving product quality. This also helps to optimize cost and energy efficiency.
Laser Based Thermal Processing
In all applications, process quality is largely determined by temperature, its spatial distribution, and its temporal variation., and pPrecise temperature regulation and control play a crucial role. In industrial furnaces, infrared (IR) emitters are frequently used as heat sources. In this context, a significant portion of the power is used to heat the chamber walls and the process atmosphere. This high thermal mass allows only slow temperature changes, and the systems reach their limits in terms of power, heating rates, and switching cycles.
Lasers, on the other hand, are ideally suited to address the above challenges above. The target substrate is heated exclusively through the absorption of laser energy. This results in selective heating of the substrate. The heating and cooling rates are essentially determined by the thermal mass of the target substrate and its optical properties. This enables, for example, the heating of a silicon carbide (SiC) substrate to 1700 K with heating rates exceeding 600 K/s. Furthermore, the direct coupling of the irradiation energy into the target substrate allows for complex temperature control.
We combine full-surface high-power thermal induction with rapid temporal modulation and spatial control. The reduced process time and improved product quality also optimize the process’s cost and energy efficiency.
Our research focuses in particular on rapid thermal processing (RTP), which benefits from both heat input and charge carrier injection. We carry out process development and machine design simultaneously, thereby modeling and optimizing heat induction in the material directly within the given industrial parameters. In addition, we apply an innovative parameter screening method that enables us to determine the optimal process window using only a few samples.
Applications of Laser-Based RTP Technology
- Heat treatments involving complex temperature profiles and high-temperature annealing steps
- Annealing steps, such as for edge passivation of half-cells
- Light soaking at moderate temperatures for SHJ solar cells
- Boron-oxygen (BO) regeneration
- Simultaneous BO regeneration and contact annealing of Ni/Cu/Ag-plated contacts
- Suppression of light and elevated temperature induced degradation (LeTID)
Our R&D Services in the Field of “Laser-Based Thermal Processing” Include:
- Development of innovative process solutions
- Detailed analysis of the resulting electronic, optical, and functional properties
- Development of component and equipment prototypes
- Thermal process simulations