LASER PROCESSING OF 22 EFFICIENT BACK-CONTACTED SILICON SOLAR CELLS

摘要

We report on a contact less and mask-free process sequence for manufacturing rear-contacted Si solar cells, reaching independently confirmed efficiencies of (22.0 ± 0.7) % on a designated cell area of 4 cm~2. We use laser structuring for creating the Rear Interdigitated contact scheme that is metallized by one Single vacuum Evaporation step (RISE). The rear of the RISE cell presented in this paper is fully covered by a thermally grown SiO_2 layer. By means of local laser ablation of an organic coating we create openings in the dielectric layer for local contacts to base and emitter. We analyze direct ablation of the passivating thermally grown SiO_2 layer by a solid-state laser with ultra-short pulses (τ_(pulse) < 15 ps) as an alternative to laser-structuring an organic coating. QSSPC lifetime measurements on samples with a P-doped shallow emitter (100Ω/sq.) result in a local diode saturation current density J_0e of (3.1 ± 0.1)×10~-12 A/cm~2 of the laser ablated region as compared to (1.4 ±0.1)×10~-12 A/cm~2 for samples with SiO_2 being removed by wet chemical etching. Short-pulse laser ablation is thus capable of avoiding wet chemical damage etching of the laser-ablated area.