Improvement of a-Si:H solar cell performance by SiH4 purging treatment

Abstract

Amorphous silicon (a-Si:H) thin film solar cells were prepared in a single chamber large area plasma enhanced chemical vapor deposition (PECVD) system. A purging process using silane (SiH4) gas was developed to remove the residual contaminations in the reactor after a nitrogen trifluoride (NF3) plasma dry cleaning process. Such a purging treatment leads to a clear improvement in initial fill factor (FF) and in efficiency of as-prepared a-Si:H solar cells. Secondary ion mass spectroscopy (SIMS) results demonstrate that fluorine impurity concentration [F] at the p-layer as well as p/i interface of solar cells reduces by more than one order of magnitude after this purging process. Additionally, high [F] is accompanied with high oxygen impurity concentration [O] which plays a great role in the solar cell performance. Low degradation rate of open circuit voltage (Voc) and fill factor (FF) of solar cells after a purging process after a 1000 h light soaking further illustrates an improvement in the material properties. Implanting such a purging process in the practical production line, about 2 W in power for a-Si:H solar modules (1.1 m × 1.3 m) are gained and meanwhile the champion solar module (1.1 m × 1.3 m) of stabilized power of 113 W with 160 nm thick intrinsic layer has been achieved.