Ag(In,Ga)Se 2 (AIGS) is one of the promising candidates for the top cell absorber in the tandem structure. However, the conversion efficiency of AIGS solar cells is still lower than that required for the top cell. In this study, to improve the conversion efficiency of AIGS solar cells, we controlled the conduction band offset (CBO) at the buffer layer/ZnO and buffer layer/AIGS interfaces. The reduction in interface recombination at the CdS buffer layer/AIGS interface was achieved by introducing a ZnS(O,OH) buffer layer instead of a CdS buffer layer, although the fill factor (FF ) decreased markedly because the CBO at the ZnS(O,OH)/ZnO interface prevented the electron flow under a forward bias. We found that the introduction of a CdS/ZnS(O,OH) hybrid buffer layer is efficient in controlling the CBO at both the buffer layer/AIGS and buffer layer/ZnO interfaces and improving the solar cell conversion efficiency.

We demonstrated the deposition of high-quality intrinsic hydrogenated amorphous silicon (i-a-Si:H) passivation layers for silicon heterojunction (SHJ) solar cells by facing target sputtering (FTS). The RF power of FTS significantly affects the electrical properties of i-a-Si:H and the passivation quality at the i-a-Si:H/crystalline silicon interface. A low surface recombination velocity of 7.0 cm/s and a relatively high deposition rate of 4.0 nm/min were simultaneously achieved at the optimum RF power. This result indicates the potential of FTS as a SiH4-free fabrication process of SHJ solar cells.

Crystalline silicon surface passivation effect of intrinsic hydrogenated amorphous silicon (i‐a‐Si:H) films deposited by radio‐frequency facing target sputtering (RF‐FTS) using a two‐step deposition technique was investigated. In the two‐step deposition technique, an i‐a‐Si:H layer was deposited at a high sputtering power condition after the deposition of i‐a‐Si:H at a low sputtering power condition. The two‐step deposition technique drastically improved the passivation quality of i‐a‐Si:H compared with a conventional single‐step deposition technique. Only 0.5‐nm‐thick i‐a‐Si:H deposited at a low sputtering power suppresses the initial sputtering damage to the crystalline silicon surface. A high average deposition rate of 14.1 nm/min was also achieved. A non‐textured silicon heterojunction solar cell using an i‐a‐Si:H passivation layer deposited by the two‐step method shows a conversion efficiency of 17.4% (Voc = 0.679 V, Jsc = 35.0 mA/cm2, FF = 0.732).