Tungsten doped indium oxide film: Ready for bifacial copper metallization of silicon heterojunction solar cell

Tungsten doped indium oxide (IWO) film was deposited by reactive plasma deposition technology for a-Si:H/c-Si heterojunction (SHJ) solar cell. The average transmittance and absorption of IWO film from 350 to 1200 nm wavelength was 88.33% and 2.16% respectively. The hall mobility is 77.8 cm2/Vs, with a corresponding carrier concentration of 2.86E20 cm−3 and resistivity of 2.80E−04 Ω cm. Based on high-performance IWO film, the 5 in. SHJ solar cell with efficiency value of 22.03% and power of 3.37 W was obtained by electroplated copper metallization technology. Compared with screen printed SHJ solar cells, the fingers of electroplated cells show finer width, higher aspect ratio and lower series resistance, resulting in increased fill factor and higher efficiency. The long term stability test of copper electroplated cells reveal that IWO film has excellent stability at the solar cell modules׳ operating temperature and can prevent copper diffusion effectively, which makes copper metallization of high efficiency heterojunction solar cell possible.