Rapid Healing: How Hydrogenation Supercharges Recovery of Electron-Irradiation Defects in Ga-doped PERC Solar Cells

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.