Influence of unintentional H2O introduction in sputtering chamber on ITO films and HJT solar cells

In this study, we investigated the effect of H2O partial pressure on the chemical characteristic and optoelectrical properties of the indium tin oxide (ITO) films and the performance and stability of heterojunction (HJT) solar cells. The H2O with varying partial pressure from 2.72 × 10−5 Pa to 8.38 × 10−5 Pa is obtained from the residual gas in the magnetron sputtering device chamber. With the H2O partial pressure raises, the resistivity of ITO films increases from 3.6 × 10−4 Ω·cm to 5.3 × 10−4 Ω·cm, and the effective total transmittance improves slightly in the near-infrared region. The efficiency of HJT solar cells with ITO films deposited at high H2O partial pressure is lower due to the deterioration of fill factor (FF), even though the short circuit current (Isc) increased. Thus, the maximum HJT solar cell efficiency of 25.30% is achieved at low H2O partial pressure. In addition, the performance of HJT solar cells under a nitrogen environment without illumination was tracked. It is observed that the high cell efficiency obtained with low H2O partial pressure has a larger degradation, which is mainly derived from the FF degradation.