Thermal stability enhancement in silicon heterojunction solar cells using deuterated intrinsic amorphous silicon passivation

This study investigates the thermal stability and passivation performance of intrinsic deuterated amorphous silicon (i-a-Si:D) as a passivation layer for silicon heterojunction (SHJ) solar cell applications. The i-a-Si:D layer is optimized by controlling its thickness, deposition power denisty and gas flow ratio to achieve enhanced passivation characteristics. The optimized i-a-Si:D layer with a thickness of 7 nm, power density of 50 mW/cm² and a D₂/SiH₄ gas ratio (GR) of 2 achieved effective lifetime (τ_eff) of 933.36 µs and an implied open-circuit voltage (iV_oc) of 0.722 V. Post-deposition deuterium plasma treatment further improved τ_eff to 1036.19 µs and iV_oc to 0.732 V. The stability analysis demonstrated that a-Si:D maintained stable τ_eff ∼ 705.11 µs and iV_oc ∼ 0.719 V under thermal stress. In contrast, intrinsic hydrogenated amorphous silicon (i-a-Si:H) exhibited significant degradation with τ_eff dropping from 879.76 µs to 545.76 µs and iV_oc decreasing from 0.722 V to 0.706 V after 16 min at 45 °C experiencing accelerated degradation. FTIR spectrum confirmed the incorporation of deuterium into the amorphous silicon matrix, strengthening the Si-D₂ bonds which enhanced thermal stability and reduced recombination. SHJ devices incorporating i-a-Si:D exhibit a lower absolute efficiency degradation of 0.6 % compared to 1.7 % for devices using i-a-Si:H after thermal incubation at 45–55 °C for 8 h. These results indicate that i-a-Si:D offers superior thermal robustness and long-term passivation stability compared to i-a-Si:H making it an ideal candidate for high-efficiency SHJ solar cells in thermally stressed environments.