Abstract
Laser doping is a typical industrial method to introduce a local highly doped region in silicon solar cells to form a selective emitter. Such a process inherently introduces defects that can be a concern to the overall performance of the solar cell. Here, we investigate the effectiveness of laser-induced defect (LasID) passivation on lifetime test structures through different annealing processes, including high-temperature belt-furnace firing, low-temperature belt-furnace annealing, and an advanced hydrogenation process (AHP) for n+ laser-doped selective emitters. We demonstrate clear advantages of post treatment using a rapid 10 s AHP at 300 °C when the lifetime structures are prefired. For the examined laser speeds of 0.5–6 m/s (sheet resistances of 4--70 Ω/□), AHP is the most effective treatment method. For example, for a typical laser doping speed of 4 m/s, starting from the same effective carrier lifetime of 36.9±2.4 μs after laser-doping step for all the passivation treatments, the AHP not only surpasses the conventional approaches by showing the highest recovery of the effective carrier lifetime (∼79% compared with ∼63% and ∼41% for the firing and belt-furnace annealing treatments, respectively) and dark saturation current density reduction in the regions affected by LasIDs but also simultaneously suppresses light-induced degradation (maximum of 4% effective lifetime degradation with respect to the passivated state, as opposed to 14% and 16% degradation for the firing and belt-furnace annealing treatments, respectively) common in Cz grown boron-doped p-type monocrystalline silicon.
Highlights
S ELECTIVE emitter structures have been used as effective pathways to enhance the performance of both n-type and p-type silicon solar cells [1]–[6].While high-temperature diffusion and photolithographybased techniques have been used to fabricate high-efficiencyManuscript received June 8, 2021; revised August 3, 2021; accepted August 10, 2021
The box pattern created for the sheet resistance and the electrochemical capacitance voltage (ECV) measurement of this laser-doping condition may be inadvertently different from when performing single line laser doping used for effective lifetime measurements
To isolate the effects associated with the laser-doped lines themselves from those of regions not influenced by laser doping, assuming there is no interaction between the laser-induced defect (LasID) and the
Summary
S ELECTIVE emitter structures have been used as effective pathways to enhance the performance of both n-type and p-type silicon solar cells [1]–[6]. A performance improvement for front laser-doped n-PERT solar cells of up to 0.84% has been reported through applying BFA [23], partly due to a considerable reduction in the J0 associated with the laser-doped region Another approach for passivating the defects created by laser doping is the implementation of a laser-annealing process. Illuminated annealing, first reported by Herguth et al [30], can electrically neutralize the defects, almost fully eliminate B–O LID [28], [30] owing to the improved mobility and reactivity of hydrogen [34] This process requires the presence of hydrogen in the bulk silicon to enable defect passivation [31], which naturally occurs in silicon solar cells during the metallization firing process, which simultaneously releases hydrogen into the bulk from the hydrogenated dielectrics.
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