Suppression of the epitaxial growth of Si films in Si heterojunction solar cells by the formation of ultra-thin oxide layers

•We apply surface oxidation to Si(111) for the suppression of epitaxial growth.•Epitaxial growth can be prevented by formation of the thin oxide layers.•a-Si/c-Si structures with oxidation have better carrier lifetimes.•The oxidation is effective to improve the performance of SHJ solar cells.

The epitaxial growth of silicon (Si) films during the catalytic chemical vapor deposition (Cat-CVD) of intrinsic amorphous Si (i-a-Si) passivation films on crystalline Si (c-Si) wafers is suppressed by the oxidation of c-Si surfaces simply by dipping the c-Si wafers in hydrogen peroxide (H2O2). This oxidation treatment is also effective for (111)-oriented c-Si surfaces particularly at high a-Si deposition temperatures. The suppression of the epitaxial growth leads to the better effective minority carrier lifetime (τeff) of c-Si wafers passivated with Cat-CVD i-a-Si films. SHJ solar cells show remarkably high open-circuit voltage (Voc) exceeding 0.7 V. These results clearly show the effectiveness of the insertion of SiOx layers on the improvement in Cat-CVD a-Si/c-Si interfaces.