In recent years, silicon heterojunction (SHJ) cells have progressed rapidly, resulting in high efficiencies [1,2] due to improvements along the production chain. Thus, an increasing market share is expected for SHJ solar cells [3,4]. Among other improvements in the production chain, an extensive light soaking can improve the efficiency up to 0.7 %abs [5,6,7]. In this work, we present the transfer of a high-intensity light soaking treatment from an offline setup to an inline laserbased rapid thermal processing (RTP) furnace. Thereby, the inline RTP treatment enables an efficiency increase of 0.3 %abs, operating at a belt speed of 700 cm/min and a processing time of 5 s. To better understand the light soaking treatment, an offline laser-based RTP setup is used beforehand to screen the temperature in a broad range at an illumination intensity of 37 kW/m². In addition to finished solar cells, TLM structures will be used, in order to separately assess contact-related effects induced by light soaking.