not-yet-known not-yet-known not-yet-known unknown Silicon heterojunction technology (HJT) and tunnel oxide passivated contacts (TOPCon) solar cell technologies are expected to dominate the photovoltaic market in the coming years. However, there are still some concerns about the long-term stability of these technologies. This work examines the effects of two widely used commercial soldering fluxes (Flux A and Flux B) on the stability of commercial silicon HJT and TOPCon solar cells. The soldering flux was applied to the solar cells, and the solar cells were annealed at 85 oC under low relative humidity. TOPCon solar cells were found to be stable; however, significant degradation was observed in the HJT solar cells after only 50 hrs. The efficiency of the HJT cells decreased by ~ 61% rel with Flux A and ~ 55% rel with Flux B, respectively. We attribute part of the observed degradation to holes present in the HJT cell metalisation after printing, which allow the soldering flux to easily penetrate the contact and subsequently react with the paste constituents. In addition, we find that the indium tin oxide (ITO) layer is very sensitive to soldering flux, showing major cracks and significant peeling after 50 hrs of annealing. Consequently, this work shows that some soldering flux can react with the ITO layer, without requiring the presence of water. This suggests that certain types of soldering flux can harm HJT solar cells even after encapsulation without the need for moisture ingress. Therefore, paying more attention to the choice of soldering flux is essential, especially when working with HJT cells. It is strongly recommended that users perform comprehensive component analysis testing on soldering fluxes before their official use rather than solely relying on datasheets provided by suppliers.

Due to their significantly lower costs than their compound semiconductor counterparts, there is increasing interest in using silicon solar cells for specific cost-sensitive applications in space, particularly in low Earth orbit (LEO). A major concern is, however, that the minority carrier lifetime (referred to henceforth as lifetime) of silicon solar cells experiences severe degradation in space due to the impact of irradiation by high-energy electrons and protons. Fortunately, thermal and hydrogenation processes can recover the lifetime losses caused by some (potentially all) defects. In this work, we study these radiation-induced defects and their recovery in detail using contactless lifetime measurement and deep-level transient spectroscopy (DLTS). Both fired and unfired industrial Ga-doped passivated emitter and rear contact (PERC) solar cell precursors are used in this work. The precursors were irradiated with 1 MeV electrons and annealed at 300 °C and 380 °C, respectively. All the irradiated samples exhibited lifetime recovery at both annealing temperatures, and the fired samples recovered significantly quicker and reached higher saturated lifetime values. After only ~360 s of annealing at 380 °C, the irradiated fired samples recovered to their pre-irradiation lifetime. In contrast, the irradiated non-fired samples required 71.5 times longer (25,740 s) at 380 °C to reach saturation. Remarkably, longer annealing times result in a reduction of the lifetime, which could be due to surface-related degradation. The DLTS measurements revealed a clear reduction of recombination active defects after annealing, including V-V + and C i-C s in irradiated fired samples and V-V + in irradiated unfired samples. This study demonstrates that the firing process is critical for optimizing the recovery of irradiation damage in silicon solar cells. Hydrogenation of the silicon bulk results in quicker recovery and superior End-of-life performance compared to thermal annealing without bulk hydrogen. Therefore, Ga PERC solar cells with bulk hydrogenation can recover radiation-induced damage, rendering it more suitable for missions in LEO.