Continued development of all-back-contact silicon wafer solar cells at ANU

The collaboration between the Solar Energy Research Institute of Singapore (SERIS), Trina Solar and ANU is progressing well, and ANU has already developed all-back-contacted (ABC) silicon wafer cells with best one-sun efficiencies of 21.2% and 22.1% on FZ material, when measured with the aperture areas of 16 cm² (includes busbars) and 13 cm² (excludes busbars) respectively. This paper presents the continuing development of ABC cells targeting the efficiency of 23.5% on 16-cm² cell area. Further developments such as optimising front surface field (FSF), rear diffusion, anti-reflection coating (ARC), and incorporation of lithographically aligned metal contacts were undertaken on the ABC cells. Phosphorus diffusion of the FSF was made lighter from the sheet resistance of 190 Ω/□ to 240 Ω/□, resulting in the reduction of the saturation current density (J_oe) of the FSF by 22 fA/cm². The optimised thickness of anti-reflection coating (ARC) PECVD SiN_x further reduces the average reflectance across the wavelength range of 300 to 1200 nm by about 4%. Incorporation of aligned metal contacts and heavier rear phosphorus diffusion has contributed to the reduction in the total series resistance by 0.08 Ωcm². The above optimised improvements have increased the efficiency of the champion ABC cell by 0.5% absolute. In addition, we present further refinements in areas of texturing; FSF passivation; electrical shading loss in terms of cell pitch, busbar and base doping; and metallisation to aim for the 16-cm² ABC cells with the conversion efficiency > 22% in the near term.