Efficiency Enhancement by Atomic Layer Deposition Based on Ultra-Thin Buffer Layers in Silicon Heterojunction Solar Cells

Atomic layer deposition (ALD) is widely used for buffer layers to mitigate sputtering damage in photovoltaic devices. A transparent conductive oxide (TCO) layer enhances carrier transport and anti-reflection in heterojunction (HJT) cells but can introduce interface defects during sputtering, increasing defect density and reducing passivation quality. This study investigates aluminum oxide (Al₂O₃ ) and tin oxide (SnO x ) as buffer layers for HJT cell passivation. These layers were deposited by ALD between doped hydrogenated amorphous silicon (a-Si:H) and TCO to reduce interface defect density. A HJT solar cell with the structure TCO/ SnOx /n-a-Si:H/i-a-Si:H/c-Si/i-a-Si:H/p-a-Si:H/Al₂O₃ /TCO was fabricated. The highest minority carrier lifetime of 2052 μs, measured using the Quasi-Steady-State Photoconductance (QSSPC) technique, was achieved with a 7 nmAl₂O₃ layer on the rear and a 7 nm SnO x layer on the front at a carrier density of 1.0 × 1015 cm−3 . OPAL 2 simulations confirmed that a 7 nm Al₂O₃layer provides optimal light absorption and minimal reflectance. Under optimal metallization, the passivated HJT cell achieved a Jsc of 40.40 mA cm−2 , V oc of 706 mV, FF of 80.45%, and efficiency of 22.95%. These results demonstrate the effectiveness of ALD deposited buffer layers in enhancing HJT performance and optimizing passivation strategies.